Lucy M Ziurys

Interests

Research

Astrochemistry, Astrobiology, Radio Astronomy, Instrumentation, High Resolution Spectroscopy, Interstellar Medium, Solar System Chemistry

Teaching

Physical Chemistry, Molecular Spectroscopy, Astrochemisty, Astrobiology, Quantum Mechanics, Radio Astronomy, Instrumentation

Courses

Scholarly Contributions

Journals/Publications

• Burton, M. A., Halfen, D. T., Lane, J. H., Ziurys, L. M., & et al, . (2020). The Structure of ScC2 (X̃2A1): A Combined Fourier Transform Microwave/Millimeter-wave Spectroscopy and Computational Study. Journal of Chemical Physics, 153, 034304.
• Burton, M. A., Tabassum, N., & Ziurys, L. M. (2020). Structure of the Model Grignard-Type Reagent ClZnCH3 (X̃1A1) by Millimeter-wave Spectroscopy. Journal of Molecular Spectroscopy, 368, 111256.
• Kim, J., Krichbaum, T. P., Broderick, A. E., Wielgus, M., Ziurys, L. M., & et al, . (2020). Event Horizon Telescope Imaging of the Archetypal Blazar 3C 279 at an Extreme 20 Microarcsecond Resolution. Astronomy & Astrophysics, 640(A69).
• Ziurys, L. M., Schmidt, D. R., & Woolf, N. J. (2020). Carbon Isotope Ratios in Planetary Nebulae: The Unexpected Enhancement of 13C. The Astrophysical Journal Letters, 900, L31.
• Akiyama, K., Alberdi, A., Alef, W., Ziurys, L. M., & et al, . (2019). First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole. Astrophysical Journal Letters.
• Akiyama, K., Alberdi, A., Alef, W., Ziurys, L. M., & et al, . (2019). First M87 Event Horizon Telescope Results. II. Array and Instrumentation. Astrophysical Journal Letters.
• Bernal, J. J., Haenecour, P., Howe, J., Ziurys, L. M., & et al, . (2019). Formation of Interstellar C60 From Silicon Carbide Circumstellar Grains. Astrophysical Journal Letters.
• Burton, M. A., & Ziurys, L. M. (2019). The Pure Rotational Spectrum of the ZnBr Radical (X2Σ+): Trends in the Zinc Halide Series. Journal of Chemical Physics.
• Burton, M. A., Russ, B. T., Bucchino, M. B., Sheridan, P. P., & Ziurys, L. M. (2019). The Ground State of KO Revisited: Millimeter and Submillimeter Spectrum of Potassium Oxide. Physical Chemistry Chemical Physics.
• Burton, M. A., Russ, B. T., Bucchino, M. P., Sheridan, P. P., & Ziurys, L. M. (2019). Quadrupole Coupling Interactions in Alkali Metal Amides MNH2 (X1A1): An Experimental and Computational Study. Journal of Molecular Spectroscopy.
• Herman, T. J., Keogh, J. P., & Ziurys, L. M. (2019). Millimeter/Sub-mm Spectroscopy of the CrBr Radical in the High Spin X6Σ+ State. Journal of Chemical Physics.
• Humphreys, R. M., Ziurys, L. M., Bernal, J. J., Gordon, M. S., & et al, . (2019). The Unexpected Spectrum of the Innermost Ejecta of the Red Hypergiant VY CMa. Astrophysical Journal Letters.
• Schmidt, D. R., & Ziurys, L. M. (2019). Exotic Carbon Chemistry in a Planetary Nebula: The Unusual Case of K4-47. Astrophysical Journal Letters.
• Ziurys, L. M. (2019). Interstellar Molecules and Their Prebiotic Potential. Handbook of Astrobiology.
• Halfen, D. T., & Ziurys, L. M. (2018). Pure Rotational Spectrum of the T-Shaped AlC2 Radical (X̃ 2A1). Physical Chemistry Chemical Physics.
• Lu, R., Krichbaum, T. P., Roy, A. L., Ziurys, L. M., & et al., . (2018). The Event-Horizon-Scale Structure of Sagittarius A* at a Resolution of 3 Schwarzschild Radii. The Astrophysical Journal.
• Schmidt, D. R., & Ziurys, L. M. (2018). The Remarkable Molecular Content of Planetary Nebulae. Astrochemistry VII: Through the Cosmos from Galaxies to Planets, Proceedings of the International Astronomical Union, IAU Symposium, 332.
• Schmidt, D. R., Zack, L. N., & Ziurys, L. M. (2018). Widespread CCH and c-C3H2 in the Helix Nebula: Unraveling the Chemical History of Hydrocarbons. Astrophysical Journal.
• Yoo, H., Kim, K., Cho, J., Choi, M., Wu, J., Evans, N. J., & Ziurys, L. M. (2018). Inflow Motions associated with High-mass Protostellar Objects. Astrophysical Journal Supplement.
• Ziurys, L. M., Halfen, D. T., & Burton, M. A. (2018). Examining Metal-Phosphorus Bonds: Submillimeter Spectroscopy of the CrP Radical (X4Σ−). Chemical Physics Letters.
• Ziurys, L. M., Halfen, D. T., & Keogh, J. P. (2018). The Sub-millimeter Spectrum of F2SO (X1A'). Journal of Molecular Spectroscopy.
• Ziurys, L. M., Schmidt, D. A., Zega, T. J., & Neville, W. J. (2018). Extreme 13C,15N,17O Isotopic Enrichment in the Young Planetary Nebula K4-47. Nature.
• Ziurys, L. M., Schmidt, D. R., & Bernal, J. J. (2018). New Circumstellar Sources of PO and PN: The Increasing Role of Phosphorus Chemistry in Oxygen-rich Stars. Astrophysical Journal.
• Bucchino, M. P., Adande, G. R., Halfen, D. T., & Ziurys, L. M. (2017). Examining Transition Metal Hydrosulfides: The Pure Rotational Spectrum of ZnSH (X̃ 2A). Journal of Chemical Physics, 147, 154313.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2017). The Pure Rotational Spectrum of the ScO (X 2) Radical. Journal of Molecular Spectroscopy, 331, 1.
• Halfen, D. T., Woolf, N. J., & Ziurys, L. M. (2017). The 12C/13C Ratio in SgrB2(N): Constraints for Galactic Chemical Evolution and Isotopic Chemistry. Astrophysical Journal, 845, 158.
• Kilchenstein, K. M., Halfen, D. T., & Ziurys, L. M. (2017). The Missing Halide: Millimeter-wave Spectroscopy of the MgI Radical (X̃ 2Σ+). Journal of Molecular Spectroscopy, 339, 1.
• Kobayashi, K., Geppert, W. D., Carrasco, N., Holm, N. G., Mousis, O., Palumbo, M., Waite, H., Wantabe, N., & Ziurys, L. M. (2017). Laboratory Studies of Methane and its Relationship to Prebiotic Chemistry. Astrobiology, 17, 786.
• Schmidt, D. R., & Ziurys, L. M. (2017). New Detections of HNC in Planetary Nebulae: Evolution of the [HCN]/[HNC] Ratio. Astrophysical Journal, 835, 79.
• Schmidt, D. R., & Ziurys, L. M. (2017). New Identifications of the CCH Radical in Planetary Nebulae: A Connection to C60?. Astrophysical Journal, 850, 123.
• Halfen, D. T., & Ziurys, L. M. (2016). Terahertz Spectroscopy of CrH (X 6Σ+) and AlH (X 1Σ+). Astrophysical Journal, 833, 89.
• Licowski, A., Halfen, D. T., & Ziurys, L. M. (2016). Millimeter/Submillimeter Spectroscopy of TiO (X 3Δr): The Rare Titanium Isotopologues. Astrophysical Journal, 833, 9.
• Ziurys, L. M. (2016). Hidden Molecules in Planetary Nebulae: New Detections of HCN and HCO+ from a Multi-object Survey. Astrophysical Journal.
• Ziurys, L. M. (2016). Rotational Spectroscopy of ClZnCH3 (X1A1): Gas-phase Synthesis and Characterization of a Monomeric Grignard-Type Reagent. Chemical Physics Letters.
• Ziurys, L. M., & Min, J. (2016). Millimeter-Wave Spectroscopy of CrC (X3Σ-) and CrCCH (X6Σ+): Examining the Chromium-Carbon Bond. Journal of Chemical Physics.
• Ziurys, L. M., Motiyenko, R. A., Margules, L., Ilyushin, V., Smirnov, I. A., & Halfen, D. T. (2016). Millimeter and Submillimeter Wave Spectra of 13C Methylamine. Astronomy & Astrophysics.
• Akiyama, K., Lu, R., Fish, V. L., Doeleman, S. S., Broderick, A. E., Dexter, J., Hada, K., Kino, M., Nagai, H., Honma, M., Johnson, M. D., Algaba, J. C., Asada, K., Brinkerink, C., Blundell, R., Bower, G. C., Cappallo, R., Crew, G. B., Dexter, M., , Dzib, S. A., et al. (2015). 230 GHz VLBI OBSERVATIONS OF M87: EVENT-HORIZON-SCALE STRUCTURE DURING AN ENHANCED VERY-HIGH-ENERGY gamma-RAY STATE IN 2012. ASTROPHYSICAL JOURNAL, 807(2).
• Anderson, J. K., Halfen, D. T., & Ziurys, L. M. (2015). The millimeter-wave spectrum of CCN ((X)over-tilde(2)Pi(r)): A combined Fourier transform and direct absorption study. JOURNAL OF MOLECULAR SPECTROSCOPY, 307, 1-5.
• Halfen, D. T., & Ziurys, L. M. (2015). SUBMILLIMETER/THz ROTATIONAL SPECTROSCOPY OF SH+ (X-3 Sigma(-)): THE COMPLETE N=1 <- 0 TRANSITION. ASTROPHYSICAL JOURNAL, 814(2).
• Halfen, D. T., Ilyushin, V. V., & Ziurys, L. M. (2015). INTERSTELLAR DETECTION OF METHYL ISOCYANATE CH3NCO IN Sgr B2(N): A LINK FROM MOLECULAR CLOUDS TO COMETS. ASTROPHYSICAL JOURNAL LETTERS, 812(1).
• Halfen, D. T., Keogh, J. P., & Ziurys, L. M. (2015). The Fourier transform microwave/millimeter-wave spectrum of YOH and YOD ((X)over-tilde(1)Sigma(+)). JOURNAL OF MOLECULAR SPECTROSCOPY, 314, 79-82.
• Johnson, M. D., Fish, V. L., Doeleman, S. S., Marrone, D. P., Plambeck, R. L., Wardle, J. F., Akiyama, K., Asada, K., Beaudoin, C., Blackburn, L., Blundell, R., Bower, G. C., Brinkerink, C., Broderick, A. E., Cappallo, R., Chael, A. A., Crew, G. B., Dexter, J., Dexter, M., , Freund, R., et al. (2015). Resolved magnetic-field structure and variability near the event horizon of Sagittarius A(star). SCIENCE, 350(6265), 1242-1245.
• Zack, L. N., Bucchino, M. P., Binns, M. K., Young, J. P., Sheridan, P. M., & Ziurys, L. M. (2015). Fourier transform microwave spectroscopy of metal nitrides and imides: Quadrupole structure in ScN (X-1 Sigma(+)), YN (X-1 Sigma(+)), and BaNH ((X)over-tilde(1)Sigma(+)). JOURNAL OF MOLECULAR SPECTROSCOPY, 317, 10-15.
• Ziurys, L. M., Adande, G. R., Edwards, J. L., Schmidt, D. R., Halfen, D. T., & Woolf, N. J. (2015). Prebiotic Chemical Evolution in the Astrophysical Context. ORIGINS OF LIFE AND EVOLUTION OF BIOSPHERES, 45(1-2), 275-288.
• Anderson, J. K., & Ziurys, L. M. (2014). DETECTION OF CCN (X-2 Pi(r)) IN IRC+10216: CONSTRAINING CARBON-CHAIN CHEMISTRY. ASTROPHYSICAL JOURNAL LETTERS, 795(1).
• Bucchino, M. P., Young, J. P., Sheridan, P. M., & Ziurys, L. M. (2014). Structural Determination and Gas-Phase Synthesis of Monomeric, Unsolvated IZnCH3 ((X)over-tilde(1)A(1)): A Model Organozinc Halide. JOURNAL OF PHYSICAL CHEMISTRY A, 118(47), 11204-11210.
• DeYonker, N. J., Halfen, D. T., Allen, W. D., & Ziurys, L. M. (2014). The Electronic Structure of Vanadium Monochloride Cation (VCl+): Tackling the Complexities of Transition Metal Species. J. Chem. Phys, 141, 204302.
• DeYonker, N. J., Halfen, D. T., Allen, W. D., & Ziurys, L. M. (2014). The electronic structure of vanadium monochloride cation (VCl+): Tackling the complexities of transition metal species. JOURNAL OF CHEMICAL PHYSICS, 141(20).
• Edwards, J. L., & Ziurys, L. M. (2014). SULFUR-AND SILICON-BEARING MOLECULES IN PLANETARY NEBULAE: THE CASE OF M2-48. ASTROPHYSICAL JOURNAL LETTERS, 794(2).
• Edwards, J. L., Cox, E. G., & Ziurys, L. M. (2014). MILLIMETER OBSERVATIONS OF CS, HCO+, AND CO TOWARD FIVE PLANETARY NEBULAE: FOLLOWING MOLECULAR ABUNDANCES WITH NEBULAR AGE. ASTROPHYSICAL JOURNAL, 791(2).
• Halfen, D. T., & Ziurys, L. M. (2014). THz SPECTROSCOPY OF AlH (X (1)Sigma(+)): DIRECT MEASUREMENT OF THE J=2 <- 1 TRANSITION. ASTROPHYSICAL JOURNAL, 791(1).
• Halfen, D. T., & Ziurys, L. M. (2014). THz Spectroscopy of AlH (X 1Σ+): Direct Measurement of the J = 2  1 Transition. ApJ, 791, 65.
• Halfen, D. T., Clouthier, D. J., & Ziurys, L. M. (2014). MILLIMETER/SUBMILLIMETER SPECTROSCOPY OF PH2CN ((X)over-tilde(1)A') AND CH3PH2((X)over-tilde(1)A'): PROBING THE COMPLEXITY OF INTERSTELLAR PHOSPHORUS CHEMISTRY. ASTROPHYSICAL JOURNAL, 796(1).
• Halfen, D. T., Clouthier, D. J., & Ziurys, L. M. (2014). The Millimeter/Submillimeter-wave Spectrum of PH2CN (X̃ 1′) and CH3PH2 (X̃ 1): Probing the Complexity of Interstellar Phosphorus Chemistry. ApJ, 796, 36.
• Li Li, ., Sun Ming, ., Li Xiao-Hua, ., Zhao Zhen-Wen, ., Ma Hui-Min, ., Gan Hai-Yong, ., Lin Zhen-Hui, ., Shi Sheng-Cai, ., & Ziurys, L. M. (2014). Recent Advances on Rotational Spectroscopy and Microwave Spectroscopic Techniques. CHINESE JOURNAL OF ANALYTICAL CHEMISTRY, 42(9), 1369-1378.
• Min, J., Halfen, D. T., & Ziurys, L. M. (2014). Fourier Transform Microwave/Millimeter-wave Spectroscopy of the ScC2 (X̃ 2A1) Radical: A Model System for Endohedral Metallofullerenes. Chem. Phys. Lett, 609, 70.
• Min, J., Halfen, D. T., & Ziurys, L. M. (2014). Fourier transform microwave/millimeter-wave spectroscopy of the ScC2 ((X)over-tilde(2)A(1)) radical: A model system for endohedral metallofullerenes. CHEMICAL PHYSICS LETTERS, 609, 70-75.
• Adande, G. R., & Ziurys, L. M. (2013). The pure rotational spectrum of VS (X⁴Σ^-): A combined Fourier transform microwave and millimeter-wave study. Journal of Molecular Spectroscopy, 290, 42-47.
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  Abstract: The pure rotational spectrum of the vanadium sulfide radical, VS (X 4Σ-), has been measured in the frequency range 5-310 GHz using a combination of millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. In the millimeter-wave region, the radical was produced in an AC discharge from the reaction of VCl4, the vanadium donor, and CS2. In the FTMW instrument, the molecule was created in a supersonic jet, coupled with a laser ablation/DC discharge source (DALAS), from a mixture of metal vapor and H2S, heavily diluted in argon. A total of 8 rotational transitions were measured for VS, in which both the quartet fine structure and vanadium hyperfine splittings were resolved. The spectra were analyzed with a Hund's case (b) Hamiltonian, and rotational, spin-rotation, spin-spin, and hyperfine parameters were determined. The precision of the constants from previous optical studies was refined and, for the first time, the vanadium quadrupole constant, eQq = -7.6 (4.0) MHz, and the third order Fermi contact correction, bS = -0.293 (94) MHz, were established. From the fine structure parameters, the nearby 4Π and 2Σ+ states were estimated to lie ∼6560 cm -1 and ∼7170 cm-1 above the ground state. The hyperfine constants suggest that the bonding in VS is partly ionic, with a significant degree of covalent character. © 2013 Elsevier Inc. All rights reserved.
• Adande, G. R., Edwards, J. L., & Ziurys, L. M. (2013). Sulfur chemistry in the envelope of VY Canis Majoris: Detailed analysis of SO and SO2 emission. Astrophysical Journal, 778(1).
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  Abstract: Detailed radiative transfer modeling has been carried out for SO 2 and SO originating in the envelope of the O-rich supergiant star VY Canis Majoris (VY CMa). A total of 27 transitions of SO2 and 7 transitions of SO lying in the energy range 3.0-138.2 cm-1 were analyzed using a new non-LTE radiative transfer code that incorporates non-spherical geometries. The spectra were primarily obtained from the Arizona Radio Observatory (ARO) 1 mm spectral survey of VY CMa, conducted with the Submillimeter Telescope; additional lines were measured with the ARO 12 m antenna at 2 and 3 mm. SO2 and SO were found to arise from five distinct outflows within the envelope, four which are asymmetric with respect to the star. Three flows arise from high-velocity red-shifted material, one from a blue-shifted wind, and the final from a classic "spherical" expansion. In the spherical component, the peak fractional abundance, relative to H2, of both molecules is f ∼ 2.5 × 10-7 at r ∼ 25 R *, and steadily decreases outward. SO2 appears to be a "parent" molecule, formed near the stellar photosphere. In the asymmetric outflows, both SO and SO2 are more prominent at large stellar radii in dense (106-107 cm -3), clumpy material, achieving their maximum abundance between 200 and 600 R * with f ∼ 3.0 × 10-8-1.5 × 10-7. These results suggest that in the collimated outflows, both species are either produced by shock chemistry or are remnant inner shell material swept up in the high-velocity winds. © 2013. The American Astronomical Society. All rights reserved.
• Adande, G. R., Woolf, N. J., & Ziurys, L. M. (2013). Observations of interstellar formamide: Availability of a prebiotic precursor in the galactic habitable zone. Astrobiology, 13(5), 439-453.
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  PMID: 23654214;PMCID: PMC3657286;Abstract: We conducted a study on interstellar formamide, NH2CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×1012 to 9.1×1013 cm-2, with rotational temperatures of 70-177 K. The molecule is thus present in warm gas, with abundances relative to H2 of 1×10-11 to 1×10-10. It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ∼0.1 mol/km2/yr or 0.18 mmol/m2 in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH 2CHO could have been available for such chemistry. © Copyright 2013, Mary Ann Liebert, Inc. 2013.
• Bucchino, M. P., & Ziurys, L. M. (2013). Terahertz spectroscopy of ²⁵MgH (X²Σ ⁺) and ⁶⁷ZnH (X²Σ⁺): Bonding in simple metal hydrides. Journal of Physical Chemistry A, 117(39), 9732-9737.
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  Abstract: Pure rotational spectra of 25MgH (X2Σ +) and 67ZnH (X2Σ+) were recorded using direct absorption techniques. These free radicals were synthesized by the reaction of metal vapor, generated in a Broida-type oven, with H2 in a dc discharge. The N = 0 → 1 and N = 1 → 2 transitions were recorded for both species in the frequency range 342-789 GHz. Spin-rotation and metal and proton hyperfine interactions were resolved in the spectra. From these data, rotational, fine structure, and hyperfine constants were determined, including the Fermi contact, dipolar, and electric quadrupole parameters of the 25Mg and 67Zn nuclei. Comparison of the metal and proton hyperfine terms suggests that the unpaired electron resides in a σ molecular orbital that has significant s contributions from both the metal and the hydrogen atoms. The dipolar terms for both metals are relatively large, in contrast to those of the proton, and indicate spσ and possibly sdσ (zinc only) orbital hybridization. The quadrupole constants arise principally from the p/d orbital character of the unpaired electron, although there is a non-negligible polarization contribution. These results suggest significant covalent character in both MgH and ZnH, in contrast to their fluoride analogs. © 2013 American Chemical Society.
• Bucchino, M. P., Sheridan, P. M., Young, J. P., Binns, M. K., Ewing, D. W., & Ziurys, L. M. (2013). Trends in alkali metal hydrosulfides: A combined Fourier transform microwave/millimeter-wave spectroscopic study of KSH (X¹A′). Journal of Chemical Physics, 139(21).
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  Abstract: The pure rotational spectrum of KSH (X1A′) has been measured using millimeter-wave direct absorption and Fourier transform microwave (FTMW) techniques. This work is the first gas-phase experimental study of this molecule and includes spectroscopy of KSD as well. In the millimeter-wave system, KSH was synthesized in a DC discharge from a mixture of potassium vapor, H2S, and argon; a discharge-assisted laser ablation source, coupled with a supersonic jet expansion, was used to create the species in the FTMW instrument. Five and three rotational transitions in the range 3-57 GHz were recorded with the FTMW experiment for KSH and KSD, respectively, in the K a = 0 component; in these data, potassium quadrupole hyperfine structure was observed. Five to six transitions with Ka = 0-5 were measured in the mm-wave region (260-300 GHz) for the two species. The presence of multiple asymmetry components in the mm-wave spectra indicates that KSH has a bent geometry, in analogy to other alkali hydrosulfides. The data were analyzed with an S-reduced asymmetric top Hamiltonian, and rotational, centrifugal distortion, and potassium electric quadrupole coupling constants were determined for both isotopolgues. The r0 geometry for KSH was calculated to be rS-H = 1.357(1) Å, rK-S = 2.806(1) Å, and θM-S-H (°) = 95.0 (1). FTMW measurements were also carried out on LiSH and NaSH; metal electric quadrupole coupling constants were determined for comparison with KSH. In addition, ab initio computations of the structures and vibrational frequencies at the CCSD(T)/6-311++G(3df,2pd) and CCSD(T)/aug-cc-pVTZ levels of theory were performed for LiSH, NaSH, and KSH. Overall, experimental and computational data suggest that the metal-ligand bonding in KSH is a combination of electrostatic and covalent forces. © 2013 AIP Publishing LLC.
• Edwards, J. L., & Ziurys, L. M. (2013). The remarkable molecular content of the red spider nebula (NGC 6537). Astrophysical Journal Letters, 770(1).
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  Abstract: Millimeter and sub-millimeter molecular-line observations of planetary nebula (PN) NGC 6537 (Red Spider) have been carried out using the Sub-Millimeter Telescope and the 12 m antenna of the Arizona Radio Observatory in the frequency range 86-692 GHz. CN, HCN, HNC, CCH, CS, SO, H2CO, HCO + and N2H+, along with the J = 3 → 2 and 6 → 5 lines of CO and those of several isotopologues, were detected toward the Red Spider, estimated to be ∼1600 yr old. This extremely high excitation PN evidently fosters a rich molecular environment. The presence of CS and SO suggest that sulfur may be sequestered in molecular form in such nebulae. A radiative transfer analysis of the CO and CS spectra indicate a kinetic temperature of T K ∼ 60-80 K and gas densities of n(H 2) ∼ 1-8 × 105 cm-3 in NGC 6537. Column densities of the molecules in the nebula and their fractional abundances relative to H2 ranged from N tot ∼ 1016 cm-2 and f ∼ 10-4 for CO, to ∼7 × 10 11 cm-2 and f ∼ 8 × 10-9 for the least abundant species, N2H+. For SO and CS, N tot ∼ 2 × 1012 cm-2 and 10 13 cm-2, respectively, with f ∼ 10-7 and 2 × 10-8. It was also found that HCN/HNC 2. A low 12C/13C ratio of ∼4 was measured, indicative of hot-bottom burning. These results, coupled with past observations, suggest that molecular abundances in PNe are governed principally by the physical and chemical properties of the individual object and its progenitor star, rather than nebular age. © 2013. The American Astronomical Society. All rights reserved.
• Halfen, D. T., Ilyushin, V. V., & Ziurys, L. M. (2013). Insights into surface hydrogenation in the interstellar medium: Observations of methanimine and methyl amine in SGR B2(N). Astrophysical Journal, 767(1).
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  Abstract: Multiple observations of methanimine (CH2NH) and methyl amine (CH3NH2) have been performed toward Sgr B2(N) at 1, 2, and 3 mm using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory. In the frequency range 68-280 GHz, 23 transitions of CH 2NH and 170 lines of CH3NH2 have been observed as individual, distinguishable features, although some are partially blended with other lines. For CH2NH, the line profiles indicate V LSR = 64.2 ± 1.4 km s-1 and ΔV 1/2 = 13.8 ± 2.8 km s-1, while V LSR = 63.7 ± 1.6 km s-1 and ΔV 1/2 = 15.1 ± 3.0 km s -1 for CH3NH2, parameters that are very similar to those of other organic species in Sgr B2(N). From these data, rotational diagrams were constructed for both species. In the case of CH2NH, a rotational temperature of T rot = 44 ± 13 K and a column density of N tot = (9.1 ± 4.4) × 1014 cm -2 were determined from the analysis. For CH3NH 2, T rot = 159 ± 30 K and N tot = (5.0 ± 0.9) × 1015 cm-2, indicating that this species is present in much warmer gas than CH2NH. The fractional abundances for CH2NH and CH3NH2 were established to be f (H2) ≈ 3.0 × 10-10 and f (H2) ≈ 1.7 × 10-9, respectively. It has been proposed that CH2NH is formed on grains via hydrogenation of HCN; further hydrogenation of CH2NH on surfaces leads to CH 3NH2. However, given the dissimilarity between the rotational temperatures and distributions of CH2NH and CH 3NH2 in Sgr B2, it is improbable that these species are closely related synthetically, at least in this source. Both CH2NH and CH3NH2 are more likely created by neutral-neutral processes in the gas phase. © 2013. The American Astronomical Society. All rights reserved.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2013). The Fourier Transform Microwave Spectrum of the YC2 (X̃ 21) Radical and its 13C Isotopologues. Chem. Phys. Lett, 555, 31.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2013). The Fourier transform microwave spectrum of YC₂ (X ̃ ² A ₁) and its ¹³C isotopologues: Chemical insight into metal dicarbides. Chemical Physics Letters, 555, 31-37.
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  Abstract: The Fourier transform microwave spectrum of YC2 (X̃2A1) and its 13C isotopologues has been measured in the 10-57 GHz range, the first FTMW study of a metal dicarbide species. The molecule was created from yttrium vapor and CH4 in argon in a supersonic jet with a discharge-assisted laser ablation source (DALAS). Rotational, fine structure, and Y and 13C hyperfine constants were determined for each isotopologue. The calculated rm(1) structure is r(Y-C) = 2.187(4) Å, r(C-C) = 1.270(4) Å, and θ(C-Y-C) = 33.74(7)°. The hyperfine parameters indicate that the unpaired electron resides principally in an sd hybridized orbital on the yttrium nucleus. © 2012 Elsevier B.V. All rights reserved.
• Lu, R., Fish, V. L., Akiyama, K., Doeleman, S. S., Algaba, J. C., Bower, G. C., Brinkerink, C., Chamberlin, R., Crew, G., Cappallo, R. J., Dexter, M., Freund, R., Friberg, P., Gurwell, M. A., T., P., Honma, M., Inoue, M., Jorstad, S. G., Krichbaum, T. P., , Loinard, L., et al. (2013). Fine-scale structure of the quasar 3C 279 measured with 1.3 mm very long baseline interferometry. Astrophysical Journal, 772(1).
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  Abstract: We report results from five day very long baseline interferometry observations of the well-known quasar 3C 279 at 1.3 mm (230 GHz) in 2011. The measured nonzero closure phases on triangles including stations in Arizona, California, and Hawaii indicate that the source structure is spatially resolved. We find an unusual inner jet direction at scales of ∼1 pc extending along the northwest-southeast direction (P.A. = 127° ± 3°), as opposed to other (previously) reported measurements on scales of a few parsecs showing inner jet direction extending to the southwest. The 1.3 mm structure corresponds closely with that observed in the central region of quasi-simultaneous super-resolution Very Long Baseline Array images at 7 mm. The closure phase changed significantly on the last day when compared with the rest of observations, indicating that the inner jet structure may be variable on daily timescales. The observed new direction of the inner jet shows inconsistency with the prediction of a class of jet precession models. Our observations indicate a brightness temperature of ∼8 × 1010 K in the 1.3 mm core, much lower than that at centimeter wavelengths. Observations with better uv coverage and sensitivity in the coming years will allow the discrimination between different structure models and will provide direct images of the inner regions of the jet with 20-30 μas (5-7 light months) resolution. © 2013. The American Astronomical Society. All rights reserved.
• Zack, L. N., & Ziurys, L. M. (2013). Chemical complexity in the helix Nebula: Multi-line observations of H2CO, HCO+, and CO. Astrophysical Journal, 765(2).
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  Abstract: Observations of CO, HCO+, and H2CO have been carried out at nine positions across the Helix Nebula (NGC 7293) using the Submillimeter Telescope and the 12 m antenna of the Arizona Radio Observatory. Measurements of the J = 1 → 0, 2 → 1, and 3 →2 transitions of CO, two transitions of HCO+ (J = 1 → 0 and 3 →2), and five lines of H2CO (J Ka, Kc = 10, 1 → 0 0, 0, 21, 2 → 11, 1, 20, 2 → 10, 1, 21, 1 → 11, 0, and 3 0, 3 →20, 2) were conducted in the 0.8, 1, 2, and 3 mm bands toward this highly evolved planetary nebula. HCO+ and H 2CO were detected at all positions, along with three transitions of CO. From a radiative transfer analysis, the kinetic temperature was found to be T K ∼ 15-40 K across the Helix with a gas density of n(H 2) ∼ 0.1-5 × 105 cm-3. The warmer gas appears to be closer to the central star, but high density material is distributed throughout the nebula. For CO, the column density was found to be N tot ∼ 0.25-4.5 × 1015 cm-2, with a fractional abundance of f (CO/H2) ∼ 0.3-6 × 10 -4. Column densities for HCO+ and H2CO were determined to be N tot ∼ 0.2-5.5 × 1011 cm -2 and 0.2-1.6 × 1012 cm-2, respectively, with fractional abundances of f (HCO+/H2) ∼ 0.3-7.3 × 10-8 and f (H2CO/H2) ∼ 0.3-2.1 × 10-7 - several orders of magnitude higher than predicted by chemical models. Polyatomic molecules in the Helix appear to be well-protected from photodissociation and may actually seed the diffuse interstellar medium. © 2013. The American Astronomical Society. All rights reserved..
• Zeigler, N. R., Zack, L. N., Woolf, N. J., & Ziurys, L. M. (2013). The Helix Nebula viewed in HCO+: Large-scale mapping of the J = 1 → 0 transition. Astrophysical Journal, 778(1).
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  Abstract: The J = 1 → 0 transition of HCO+ at 89 GHz has been mapped across the Helix Nebula (NGC 7293) with 70″ spatial resolution (1.68 km s-1 velocity resolution) using the Arizona Radio Observatory 12 m telescope. This work is the first large-scale mapping project of a dense gas tracer (n(H2) ∼ 105 cm-3) in old planetary nebulae. Observations of over 200 positions encompassing the classical optical image were conducted with a 3σ noise level of ∼20 mK. HCO+ was detected at most positions, often exhibiting multiple velocity components indicative of complex kinematic structures in dense gas. The HCO+ spectra suggest that the Helix is composed of a bipolar, barrel-like structure with red- and blue-shifted halves, symmetric with respect to the central star and oriented ∼10° east from the line of sight. A second bipolar, higher velocity outflow exists as well, situated along the direction of the Helix "plumes." The column density of HCO+ across the Helix is N tot ∼ 1.5 × 1010-5.0 × 1011 cm-2, with an average value N ave ∼ 1 × 10 11 cm-2, corresponding to an abundance, relative to H 2, of f ∼ 1.4 × 10-8. This value is similar to that observed in young PN, and contradicts chemical models, which predict that the abundance of HCO+ decreases with nebular age. This study indicates that polyatomic molecules readily survive the ultraviolet field of the central white dwarf, and can be useful in tracing nebular morphology in the very late stages of stellar evolution. © 2013. The American Astronomical Society. All rights reserved.
• Adande, G. R., & Ziurys, L. M. (2012). Millimeter-wave observations of CN and HNC and their ¹⁵N isotopologues: A new evaluation of the ¹⁴N/¹⁵N ratio across the galaxy. Astrophysical Journal, 744(2).
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  Abstract: The N= 1→ 0 transitions of CN and C15N (X 2Σ+), as well as the J= 1→ 0 lines of HN 13C and H15NC, have been observed toward 11 molecular clouds using the new 3 mm ALMA-type receiver of the 12 m telescope of the Arizona Radio Observatory. These sources span a wide range of distances from the Galactic center and are all regions of star formation. From these observations, 14N/15N ratios have been determined using two independent methods. First, the measurements of C14N and C15N were directly compared to establish this ratio, correcting for high opacities when needed, as indicated by the nitrogen hyperfine intensities. Second, the ratio was calculated from the quantity [HN13C]/[H15NC], determined from the HNC data, and then scaled by 12C/13C ratios previously established, i.e., the so-called double isotope method. Values from both methods are in reasonable agreement, and fall in the range 120-400, somewhat lower than previous 14N/15N ratios derived from HCN. The ratios exhibit a distinct positive gradient with distance from the Galactic center, following the relationship14N/15N= 21.1 (5.2)kpc-1 D GC + 123.8 (37.1). This gradient is consistent with predictions of Galactic chemical evolution models in which 15N has a secondary origin in novae, while primary and secondary sources exist for 14N. The local interstellar medium value was found to be 4N/15N= 290 40, in agreement with the ratio found in nearby diffuse clouds and close to the value of 272 found in Earth's atmosphere. © 2012 The American Astronomical Society. All rights reserved.
• Adande, G. R., Halfen, D. T., & Ziurys, L. M. (2012). Fourier transform microwave spectroscopy of ScS (X ²Σ ⁺) and YS (X ²Σ ⁺). Journal of Molecular Spectroscopy, 278(1), 35-40.
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  Abstract: The pure rotational spectra of the transition metal sulfide radicals ScS and YS in their 2Σ + ground states have been measured in the range 8-48 GHz using Fourier transform microwave (FTMW) spectroscopy. The radicals were synthesized from the reaction of metal vapor, produced by laser ablation, and H 2S gas, heavily diluted in argon. A DC discharge was needed in the case of ScS. Four rotational transitions were recorded for each molecule, in which multiple fine and hyperfine components were resolved. The spectra were analyzed with a case (b) Hamiltonian, and rotational, fine, and hyperfine constants were determined for both molecules, improving the precision of previous parameters established from optical and double resonance data. The quadrupole coupling constant eQq has been accurately established for ScS for the first time, as well. From the rotational constants, the bond lengths were determined to be 2.1288 Å for ScS and 2.2614 Å for YS. The hyperfine parameters suggest that, although ScS and YS are principally ionic molecules, they are more covalent than their oxygen analogs. © 2012 Elsevier Inc. All rights reserved.
• Doeleman, S. S., Fish, V. L., Schenck, D. E., Beaudoin, C., Blundell, R., Bower, G. C., Broderick, A. E., Chamberlin, R., Freund, R., Friberg, P., Gurwell, M. A., Ho, P. T., Honma, M., Inoue, M., Krichbaum, T. P., Lamb, J., Loeb, A., Lonsdale, C., Marrone, D. P., , Moran, J. M., et al. (2012). 1.3mm VLBI detections of M87 (Doeleman+, 2012). VizieR Online Data Catalog, 210, 33801.
• Halfen, D. T., Sun, M., Clouthier, D. J., & Ziurys, L. M. (2012). The microwave and millimeter rotational spectra of the PCN radical (X̃ ³∑ ^-). Journal of Chemical Physics, 136(14).
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  PMID: 22502523;Abstract: The pure rotational spectrum of the PCN radical (X̃ 3∑ -) has been measured for the first time using a combination of millimeter/submillimeter direct absorption and Fourier transform microwave (FTMW) spectroscopy. In the millimeter instrument, PCN was created by the reaction of phosphorus vapor and cyanogen in the presence of an ac discharge. A pulsed dc discharge of a dilute mixture of PCl 3 vapor and cyanogen in argon was the synthetic method employed in the FTMW machine. Twenty-seven rotational transitions of PCN and six of P 13CN in the ground vibrational state were recorded from 19 to 415 GHz, all which exhibited fine structure arising from the two unpaired electrons in this radical. Phosphorus and nitrogen hyperfine splittings were also resolved in the FTMW data. Rotational satellite lines from excited vibrational states with v 2 = 1-3 and v 1 = 1 were additionally measured in the submillimeter range. The data were analyzed with a Hund's case (b) effective Hamiltonian and rotational, fine structure, and hyperfine constants were determined. From the rotational parameters of both carbon isotopologues, the geometry of PCN was established to be linear, with a P-C single bond and a C-N triple bond, structurally comparable to other non-metal main group heteroatom cyanides. Analysis of the hyperfine constants suggests that the two unpaired electrons reside almost exclusively on the phosphorus atom in a π 2 configuration, with little interaction with the nitrogen nucleus. The fine structure splittings in the vibrational satellite lines differ significantly from the pattern of the ground state, with the effect most noticeable with increasing v 2 quantum number. These deviations likely result from spin-orbit vibronic perturbations from a nearby 1∑ + state, suggested by the data to lie ∼12 000 cm -1 above the ground state. © 2012 American Institute of Physics.
• Liszt, H. S., & Ziurys, L. M. (2012). Carbon isotope fractionation and depletion in TMC1. Astrophysical Journal, 747(1).
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  Abstract: 12C/ 13C isotopologue abundance anomalies have long been predicted for gas-phase chemistry in molecules other than CO and have recently been observed in the Taurus molecular cloud (TMC) in several species hosting more than one carbon atom, i.e., CCH, CCS, CCCS, and HC 3N. Here we work to ascertain whether these isotopologic anomalies actually result from the predicted depletion of the 13C + ion in an oxygen-rich optically shielded dense gas, or from some other more particular mechanism or mechanisms. We observed λ3mm emission from carbon-, sulfur-, and nitrogen-bearing isotopologues of HNC, CS, and H 2CS at three positions in Taurus (TMC1, L1527, and the NH 3 peak) using the ARO 12 m telescope. We saw no evidence of 12C/ 13C anomalies in our observations. Although the pool of C + is likely to be depleted in 13C, 13C is not depleted in the general pool of carbon outside CO, which probably exists mostly in the form of C 0. The observed isotopologic abundance anomalies are peculiar to those species in which they are found. © 2012. The American Astronomical Society. All rights reserved.
• Lu, R., Fish, V. L., Weintroub, J., Doeleman, S. S., Bower, G. C., Freund, R., Friberg, P., T., P., Honma, M., Inoue, M., Krichbaum, T. P., Marrone, D. P., Moran, J. M., Oyama, T., Plambeck, R., Primiani, R., Shen, Z., P., R., Wright, M., , Young, K. H., et al. (2012). Resolving the inner JET structure of 1924-292 with the event horizon telescope. Astrophysical Journal Letters, 757(1).
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  Abstract: We present the first 1.3mm (230GHz) very long baseline interferometry model image of an active galactic nucleus (AGN) jet using closure phase techniques with a four-element array. The model image of the quasar 1924-292 was obtained with four telescopes at three observatories: the James Clerk Maxwell Telescope on Mauna Kea in Hawaii, the Arizona Radio Observatory's Submillimeter Telescope in Arizona, and two telescopes of the Combined Array for Research in Millimeter-wave Astronomy in California in 2009 April. With the greatly improved resolution compared with previous observations and robust closure phase measurement, the inner jet structure of 1924-292 was spatially resolved. The inner jet extends to the northwest along a position angle of -53° at a distance of 0.38mas from the tentatively identified core, in agreement with the inner jet structure inferred from lower frequencies, and making a position angle difference of ∼80° with respect to the centimeter jet. The size of the compact core is 0.15pc with a brightness temperature of 1.2 × 10 11K. Compared with those measured at lower frequencies, the low brightness temperature may argue in favor of the decelerating jet model or particle-cascade models. The successful measurement of closure phase paves the way for imaging and time resolving Sgr A* and nearby AGNs with the Event Horizon Telescope. © 2012 The American Astronomical Society. All rights reserved.
• Min, J., Halfen, D. T., Sun, M., Harris, B., & Ziurys, L. M. (2012). The microwave and millimeter spectrum of ZnCCH (X̃ ²Σ ⁺): A new zinc-containing free radical. Journal of Chemical Physics, 136(24).
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  PMID: 22755577;Abstract: The pure rotational spectrum of the ZnCCH (X̃ 2Σ +) radical has been measured using Fourier transform microwave (FTMW) and millimeter direct-absorption methods in the frequency range of 7-260 GHz. This work is the first study of ZnCCH by any type of spectroscopic technique. In the FTMW system, the radical was synthesized in a mixture of zinc vapor and 0.05 acetylene in argon, using a discharge assisted laser ablation source. In the millimeter-wave spectrometer, the molecule was created from the reaction of zinc vapor, produced in a Broida-type oven, with pure acetylene in a dc discharge. Thirteen rotational transitions were recorded for the main species, 64ZnCCH, and between 4 and 10 for the 66ZnCCH, 68ZnCCH, 64ZnCCD, and 64Zn 13C 13CH isotopologues. The fine structure doublets were observed in all the data, and in the FTMW spectra, hydrogen, deuterium, and carbon-13 hyperfine splittings were resolved. The data have been analyzed with a 2Σ Hamiltonian, and rotational, spin-rotation, and H, D, and 13C hyperfine parameters have been established for this radical. From the rotational constants, an r m(1) structure was determined with r Zn-C = 1.9083 Å, r C-C = 1.2313 Å, and r C-H = 1.0508 Å. The geometry suggests that ZnCCH is primarily a covalent species with the zinc atom singly bonded to the C≡C-H moiety. This result is consistent with the hyperfine parameters, which suggest that the unpaired electron is localized on the zinc nucleus. The spin-rotation constant indicates that an excited 2Π state may exist ∼19 000 cm -1 in energy above the ground state. © 2012 American Institute of Physics.
• Müller, H. S., Halfen, D. T., & Ziurys, L. M. (2012). The spectroscopic parameters of sodium cyanide, NaCN (X ¹A′), revisited. Journal of Molecular Spectroscopy, 272(1), 23-26.
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  Abstract: The study of the rotational spectrum of NaCN (X 1A′) has recently been extended in frequency and in quantum numbers. Difficulties have been encountered in fitting the transition frequencies within experimental uncertainties. Various trial fits traced the difficulties to the incomplete diagonalization of the Hamiltonian. Employing fewer spectroscopic parameters than before, the transition frequencies could be reproduced within experimental uncertainties on average. Predictions of a-type R-branch transitions with K a ≤ 7 up to 570 GHz should be reliable to better than 1 MHz. In addition, modified spectroscopic parameters have been derived for the 13C isotopic species of NaCN. © 2012 Elsevier Inc. All rights reserved.
• Savin, D. W., Brickhouse, N. S., Cowan, J. J., Drake, R. P., Federman, S. R., Ferland, G. J., Frank, A., Gudipati, M. S., Haxton, W. C., Herbst, E., Profumo, S., Salama, F., Ziurys, L. M., & Zweibel, E. G. (2012). The impact of recent advances in laboratory astrophysics on our understanding of the cosmos. Reports on Progress in Physics, 75(3).
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  PMID: 22790424;Abstract: An emerging theme in modern astrophysics is the connection between astronomical observations and the underlying physical phenomena that drive our cosmos. Both the mechanisms responsible for the observed astrophysical phenomena and the tools used to probe such phenomena - the radiation and particle spectra we observe - have their roots in atomic, molecular, condensed matter, plasma, nuclear and particle physics. Chemistry is implicitly included in both molecular and condensed matter physics. This connection is the theme of the present report, which provides a broad, though non-exhaustive, overview of progress in our understanding of the cosmos resulting from recent theoretical and experimental advances in what is commonly called laboratory astrophysics. This work, carried out by a diverse community of laboratory astrophysicists, is increasingly important as astrophysics transitions into an era of precise measurement and high fidelity modeling. © 2012 IOP Publishing Ltd.
• Sun, M., Halfen, D. T., Min, J., Clouthier, D. J., & Ziurys, L. M. (2012). Gas-phase rotational spectroscopy of AlCCH (X̃ ¹Σ ⁺): A model system for organo-aluminum compounds. Chemical Physics Letters, 553, 11-16.
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  Abstract: The pure rotational spectrum of AlCCH in its ground electronic state (X̃ 1Σ +) has been measured using Fourier transform microwave (FTMW) and mm/sub-mm direct absorption spectroscopy. AlCCH was created in a DC discharge from HCCH and aluminum vapor, either produced by a Broida-type oven, or generated from Al(CH 3) 3 in a supersonic jet source. Rotational transitions were measured for five isotopologues of AlCCH, with 13C and deuterium substitutions. From these data, rotational and Al and D quadrupole parameters were determined, as well as an accurate structure. AlCCH appears to exhibit an acetylenic arrangement with significant covalent character in the Al-C single bond. © 2012 Elsevier B.V. All rights reserved.
• Zack, L. N., Sun, M., Bucchino, M. P., Clouthier, D. J., & Ziurys, L. M. (2012). Gas-phase synthesis and structure of monomeric ZnOH: A model species for metalloenzymes and catalytic surfaces. Journal of Physical Chemistry A, 116(6), 1542-1550.
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  PMID: 22224369;Abstract: Monomeric ZnOH has been studied for the first time using millimeter and microwave gas-phase spectroscopy. ZnOH is important in surface processes and at the active site of the enzyme carbonic anhydrase. In the millimeter-wave direct-absorption experiments, ZnOH was synthesized by reacting zinc vapor, produced in a Broida-type oven, with water. In the Fourier-transform microwave measurements, ZnOH was produced in a supersonic jet expansion of CH 3OH and zinc vapor, created by laser ablation. Multiple rotational transitions of six ZnOH isotopologues in their X 2A′ ground states were measured over the frequency range of 22-482 GHz, and splittings due to fine and hyperfine structure were resolved. An asymmetric top pattern was observed in the spectra, showing that ZnOH is bent, indicative of covalent bonding. From these data, spectroscopic constants and an accurate structure were determined. The Zn-O bond length was found to be similar to that in carbonic anhydrase and other model enzyme systems. © 2012 American Chemical Society.
• Ziurys, L. M. (2012). Detection of Jet Launching Structure Near the Supermassive Black Hole in M87. Science.
• Ziurys, L. M. (2015). First 230 GHz VLBI Observation of Blazar 3C 279 Using the Apex Telescope. Astronomy & Astrophysics.
• Ziurys, L. M. (2015). The Search for a Complex Molecule in a Selected Hot Core Region: A Rigorous Attempt to Confirm trans-Ethyl Methyl Ether toward W51 e1/e2. Astrophysical Journal.
• Flory, M. A., & Ziurys, L. M. (2011). Millimeter-wave rotational spectroscopy of FeCN (X⁴Δ _i) and FeNC (X⁶Δ_i): Determining the lowest energy isomer. Journal of Chemical Physics, 135(18).
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  PMID: 22088061;Abstract: The pure rotational spectrum of FeCN has been recorded in the frequency range 140-500 GHz using millimetersub-millimeter direct absorption techniques. The species was created in an ac discharge of Fe(CO)5 and cyanogen. Spectra of the 13C, 54Fe, and 57Fe isotopologues were also measured, confirming the linear cyanide structure of this free radical. Lines originating from several Renner-Teller components in the v2 bending mode were also observed. Based on the observed spin-orbit pattern, the ground state of FeCN is 4Δi, with small lambda-doubling splittings apparent in the Ω = 5/2, 3/2, and 1/2 components. In addition, a much weaker spectrum of the lowest spin-orbit component of FeNC, Ω = 9/2, was recorded; these data are consistent with the rotational parameters of previous optical studies. The data for FeCN were fit with a Hunds case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling parameters were determined. Rotational constants were also established from a case (c) analysis for the other isotopologues, excited vibronic states, and for FeNC. The r0 bond lengths of FeCN were determined to be rFe-C = 1.924 Å and rC-N = 1.157 Å, in agreement with theoretical predictions for the 4Δ i state. These measurements indicate that FeCN is the lower energy isomer and is more stable than FeNC by ∼1.9 kcalmol. © 2011 American Institute of Physics.
• Freund, R. W., Ziurys, L. M., Reiland, G. P., & Lauria, E. F. (2011). New technical and scientific developments at the Arizona radio observatory. 2011 30th URSI General Assembly and Scientific Symposium, URSIGASS 2011.
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  Abstract: Astronomical observations in the millimeter and sub-millimeter regions are performed at the two facilities of the Arizona Radio Observatory (ARO). The Sub-Millimeter Telescope (SMT) located on Mount Graham utilizes 3 heterodyne SIS receivers to cover 3 of the 4 atmospheric windows from 210 to 720 GHz and soon a new receiver will cover the remaining window. The 12-Meter telescope located on Kitt Peak use 3 heterodyne SIS receivers to the cover the 2 windows from 68 to 180 GHz. All receivers now employ orthogonal polarization optics and soon 4 will utilize wideband dual channel sideband separating mixer technology. Presented here are new instrumentation developments and recent scientific results from the ARO. © 2011 IEEE.
• Halfen, D. T., & Ziurys, L. M. (2011). Millimeter and submillimeter rest frequencies for NaCN (X̃ ¹A′): A remarkably abundant circumstellar molecule. Astrophysical Journal, 730(2).
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  Abstract: The pure rotational spectrum of NaCN has been recorded in the millimeter/submillimeter region using direct absorption techniques, the first experimental study of this molecule at frequencies above 40GHz. The species was produced in the gas phase in an AC discharge by the reaction of sodium vapor with cyanogen. Twelve rotational transitions of NaCN have been measured in the range of 180-530GHz, extending the previous microwave data to millimeter/submillimeter frequencies. Multiple Ka asymmetry components were recorded in each rotational transition up to Ka = 5 or 6, a total of 131 individual lines. These data have been analyzed with a standard asymmetric top Hamiltonian, combined with prior microwave measurements. Higher-order centrifugal distortion terms were clearly needed to model the millimeter-wave transitions of this floppy molecule. From this revised set of spectroscopic constants, accurate frequency predictions can now be made up to 600GHz for NaCN for the lower-value Ka components (Ka ≤ 4). Based on the new laboratory data and past spectral surveys, a revised abundance for NaCN in IRC+10216 has been estimated. For a 5″ source, the fractional abundance for this molecule was found to be f (NaCN/H2) 1× 10-8, comparable to that of c-C3H2. These new frequency measurements should aid in line identification in surveys in the 0.8 mm band and at shorter wavelengths. © 2011. The American Astronomical Society. All rights reserved.
• Halfen, D. T., Clouthier, D. J., Ziurys, L. M., Lattanzi, V., McCarthy, M. C., Thaddeus, P., & Thorwirth, S. (2011). The pure rotational spectrum of HPS (X̃¹A′): Chemical bonding in second-row elements. Journal of Chemical Physics, 134(13).
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  PMID: 21476750;Abstract: The pure rotational spectrum of HPS, as well as its 34S and D isotopologues, has been recorded at microwave, millimeter, and submillimeter wavelengths, the first observation of this molecule in the gas phase. The data were obtained using a combination of millimeter direct absorption, Fourier transform microwave (FTMW), and microwave-microwave double-resonance techniques, which cover the total frequency range from 15 to 419 GHz. Quantum chemical calculations at the B3LYP and CCSD(T) levels were also performed to aid in spectral identification. HPS was created in the direct absorption experiment from a mixture of elemental phosphorus, H2S, and Ar carrier gas; DPS was produced by adding D2. In the FTMW study, these species were generated in a pulsed discharge nozzle from PH3 and H2S or D2S, diluted in neon. The spectra recorded for HPS and its isotopologues exhibit clear asymmetric top patterns indicating bent structures; phosphorus hyperfine splittings were also observed in HPS, but not DPS. Analysis of the data yielded rotation, centrifugal distortion, and phosphorus nuclear spin-rotation parameters for the individual species. The rm(1) structure for HPS, calculated from the rotational constants, is r(H-P) = 1.438(1) Å, r(P-S) = 1.9320(1) Å, and θ(H-P-S) = 101.85(9). Empirically correcting for zero-point vibrational effects yields the geometry re(H-P) = 1.4321(2) Å, re(P-S) = 1.9287(1) Å, and θe(H-P-S) = 101.78(1), in close agreement with the rm(1) structure. A small inertial defect was found for HPS indicating a relatively rigid molecule. Based on these data, the bonding in this species is best represented as H-PS, similar to the first-row analog HNO, as well as HNS and HPO. Therefore, substitution of phosphorus and sulfur for nitrogen and oxygen does not result in a dramatic structural change. © 2011 American Institute of Physics.
• Halfen, D. T., Ilyushin, V., & Ziurys, L. M. (2011). Formation of peptide bonds in space: A comprehensive study of formamide and acetamide in Sgr B2(N). Astrophysical Journal, 743(1).
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  Abstract: Extensive observations of acetamide (CH3CONH2) and formamide (NH2CHO) have been conducted toward Sgr B2(N) at 1, 2, and 3mm using the Submillimeter Telescope (SMT) and the 12m antenna of the Arizona Radio Observatory. Over the frequency range 65-280GHz, 132 transitions of acetamide have been observed as individual, distinguishable features, although in some cases they are partially blended. The unblended transitions in acetamide indicate V LSR= 63.2 2.8kms-1 and ΔV 1/2= 12.5 2.9kms-1, line parameters that are very similar to that of formamide (NH2CHO) and other organic species in Sgr B2(N). For formamide, 79 individual transitions were identified over the same frequency region. Rotational diagram analyses indicate the presence of two components for both species in Sgr B2(N). For acetamide, the colder component (Eu < 40K) exhibits a rotational temperature of T rot= 17 4K and a column density of N tot= 5.2 3.5× 10 13cm-2; the higher energy component has T rot= 171 4K and N tot= 6.4 4.7× 1014cm-2. In the case of formamide, T rot= 26 4K and N tot= 1.6 0.7× 1014cm-2 for the colder component with T rot= 134 17K and N tot= 4.0 ± 1.2× 10 14cm-2 for the warmer region. The fractional abundances of acetamide are f (H2)= 1.7× 10-11 and 2.1× 10-10 for the cold and warm components, and in formamide, f (H 2)= 5.3× 10-11 and 1.3× 10-10. The similarity between the abundances and distributions of CH3CONH 2 and NH2CHO suggests a synthetic connection. The abundance of acetamide, moreover, is only a factor of three lower than that of formaldehyde, and very similar to acetaldehyde and ketene. CH 3CONH2 is therefore one of the most abundant complex organic species in Sgr B2(N), and could be a possible source of larger peptide molecules, as opposed to amino acids. © 2011. The American Astronomical Society. All rights reserved.
• Pulliam, R. L., Edwards, J. L., & Ziurys, L. M. (2011). Circumstellar ion-molecule chemistry: Observations of HCO⁺ in the envelopes of O-rich stars and IRC+10216. Astrophysical Journal, 743(1).
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  Abstract: Millimeter-wave observations of HCO+ have been conducted toward oxygen-rich circumstellar envelopes, as well as IRC+10216, using the facilities of the Arizona Radio Observatory (ARO). The J= 1→ 0 and 2→ 1 transitions of this molecule were measured with the ARO 12m antenna, while the J= 3→ 2 and 4→ 3 lines were observed using the ARO Sub-Millimeter Telescope. HCO+ was detected toward the supergiant NMLCyg and the asymptotic giant branch (AGB) stars IK Tau, TX Cam, and W Hya in at least two transitions. The J= 2→ 1 and 3→ 2 lines of this ion were also detected toward IRC+10216, confirming the identification of HCO+ in this object. The line profiles measured for HCO+ toward NMLCyg consist of red- and blueshifted components, suggesting a non-spherical shell. Based on a radiative transfer analysis, the abundances in the O-rich envelopes were f(HCO+/H2) ∼0.15-1.3× 10-7, with the AGB stars typically exhibiting the higher values. In IRC+10216, f(HCO +/H2) ∼4.1× 10-9, lower than the O-rich counterparts. The abundances of HCO+ were also found to peak at considerable distances from the star, indicative of an outer envelope molecule. Comparison with H2O and CO, the main precursor species, suggests that HCO+ is more prevalent in envelopes that have substantial water, but CO also plays a role in its formation. The abundance of HCO+ appears to increase inversely with mass-loss rate, provided the rate is >10-6 M⊙yr-1. The common appearance of HCO+ in circumstellar gas indicates that, at some level, ion-molecule reactions influence the chemistry of evolved stellar envelopes. © 2011. The American Astronomical Society. All rights reserved.
• Sheridan, P. M., Binns, M. K., Sun, M., Min, J., Bucchino, M. P., Halfen, D. T., & Ziurys, L. M. (2011). Fourier transform microwave spectroscopy of LiCCH, NaCCH, and KCCH: Quadrupole hyperfine interactions in alkali monoacetylides. Journal of Molecular Spectroscopy, 269(2), 231-235.
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  Abstract: The alkali metal monoacetylides LiCCH, NaCCH, and KCCH and their deuterium isotopologues have been investigated using Fourier transform microwave (FTMW) spectroscopy in the frequency range 5-37 GHz. The molecules were synthesized in a supersonic expansion by the reaction of metal vapor, produced by laser ablation, with acetylene or DCCD. Use of target rods of the pure metal and a DC discharge immediately following the laser interaction region were significant factors in molecule production. Multiple rotational transitions were recorded for all species, except where only the J = 1 → 0 line was accessible (Li species). Quadrupole hyperfine interactions arising from the metal nuclei were resolved in each molecule, as well as those from the deuterium nucleus in the deuterated isotopologues. From a combined analysis with previous millimeter-wave data, refined rotational constants were determined for these species, as well as 7Li, 23Na, 39K, and D eQq parameters. The values of the metal quadrupole coupling constants are comparable to those of the alkali halides and hydroxides, indicating a similar degree of ionic character in the metal-ligand bond. © 2011 Elsevier Inc. All rights reserved.
• Zack, L. N., Halfen, D. T., & Ziurys, L. M. (2011). Detection of FeCN (X ⁴ Δ _i) in IRC+10216: A new interstellar molecule. Astrophysical Journal Letters, 733(2 PART 2).
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  Abstract: A new interstellar molecule, FeCN (X 4Δ i ), has been detected in the envelope of the carbon-rich asymptotic giant branch star, IRC+10216. This work is the first definitive detection of an iron-bearing molecule in the interstellar medium and is based on newly measured rest frequencies. Eight successive rotational transitions of this linear free radical in the lowest spin ladder, Ω = 7/2, were observed at 2 and 3 mm using the Arizona Radio Observatory (ARO) 12 m telescope. Three transitions appear as single, unblended features at the 1-2 mK level and exhibit characteristic IRC+10216 line profiles; one had previously been observed with the IRAM 30 m telescope. Two other transitions are partially blended, but exhibit distinct emission at the FeCN frequencies. The remaining transitions are either completely contaminated, or are too high in energy. Comparison of the ARO and IRAM data suggests a source size for FeCN of 30″ in IRC+10216, indicating an outer shell distribution, as expected for a free radical. The column density derived for FeCN is N tot = 8.6 × 1011cm -2 with a rotational temperature of T rot = 21 K. The fractional abundance of this molecule is [FeCN]/[H2] 2-7 × 10-10 - comparable to that of MgCN and KCN in IRC+10216. FeCN is likely formed by gas-phase reactions of Fe+ or neutral iron; the latter has a significant gas-phase abundance in the outer shell. The detection of FeCN is further evidence that metal cyanides/isocyanides dominate the chemistry of refractory elements in IRC+10216. © 2011. The American Astronomical Society. All rights reserved.
• Zack, L. N., Min, J., Harris, B. J., Flory, M. A., & Ziurys, L. M. (2011). Fourier-transform microwave spectroscopy of FeCN (X⁴Δ _i): Confirmation of the quartet electronic ground state. Chemical Physics Letters, 514(4-6), 202-206.
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  Abstract: Spectra of the FeCN radical have been measured using Fourier-transform microwave (FTMW) techniques. This species was created in a supersonic jet by laser-ablation of iron, coupled with a dc discharge, in the presence (CN) 2. The lowest rotational transition of FeCN near 36 GHz was recorded. The observation of this transition, the J = 9/2 → 7/2 line in the Ω = 7/2 spin-orbit component, conclusively establishes that FeCN has a 4Δi ground electronic state, rather a 6Δ state, as predicted by theory. The FTMW spectrum of NiCN (X2Δi) was also measured; small nitrogen hyperfine splitting was observed in both molecules. © 2011 Elsevier B.V. All rights reserved.
• Adande, G. R., Halfen, D. T., Ziurys, L. M., Quan, D., & Herbst, E. (2010). Observations of the [HNCS]/[HSCN] ratio in Sgr B2 and TMC-1: Evidence for low-temperature gas-phase chemistry. Astrophysical Journal Letters, 725(1), 561-570.
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  Abstract: Millimeter observations of isothiocyanic acid (HNCS) and its higher energy isomer, thiocyanic acid (HSCN), have been carried out toward Sgr B2 and TMC-1 using the 12 m telescope of the Arizona Radio Observatory. For both species, the JKa,Kc =80,8→70,7 and 9 0,9→80,8 transitions near 91-93 GHz and 103-106 GHz were mapped across a 6′ × 3′ region, centered near Sgr B2(M). Comparativemapping observations were also done for the JKa,Kc =40,4→ 30,3 line of HNCO and HOCN near 84-87 GHz. In addition, the J Ka,Kc = 70,7 → 60,6 and 80,8 → 7 0,7 transitions of both HNCS and HSCN were detected in TMC-1, the first identification of either molecule in a cold, dark cloud. Emission from HNCS and HSCN was found to be extended over the Sgr B2 cloud, with a single velocity component and a linewidth of ∼20-25 km s-1. Column densities derived for HSCN in Sgr B2 are typically Ntot ∼ (0.2-1) × 1013 cm-2,with Ntot ∼(0.8-5)×10 13 cm-2 for the more stable isomer, HNCS. In TMC-1, these species have similar column densities of (6-8) × 1010 cm-2. The [HNCS]/[HSCN] abundance ratio ranges from 2 to 7 in Sgr B2, with a value of ∼1 in TMC-1. In contrast, the [HNCO]/[HOCN] ratio in Sgr B2 is ∼110-250. Gas-grain chemical models do not reproduce the observed abundances of the sulfur isomers in either source. Given the energy difference of over 3200 K between HNCS and HSCN, these observations suggest that both molecules are produced from gas-phase, ion-molecule chemistry with a common precursor, HNCSH+. The oxygen analogs, in contrast, probably have a more complex chemical network, perhaps involving the H2NCO+ precursor, which preferentially leads to HNCO. © 2010. The American Astronomical Society.
• Flory, M. A., Apponi, A. J., Zack, L. N., & Ziurys, L. M. (2010). Activation of methane by zinc: Gas-phase synthesis, structure, and bonding of HZnCH₃. Journal of the American Chemical Society, 132(48), 17186-17192.
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  PMID: 21077609;Abstract: The methylzinc hydride molecule, HZnCH3, has been observed in the gas phase for the first time in the monomeric form using high-resolution spectroscopic techniques. The molecule was synthesized by two methods: the reaction of dimethylzinc with hydrogen gas and methane in an AC discharge and the reaction of zinc vapor produced in a Broida-type oven with methane in a DC discharge. HZnCH3 was identified on the basis of its pure rotational spectrum, which was recorded using millimeter/submillimeter direct-absorption and Fourier transform microwave techniques over the frequency ranges 332-516 GHz and 18-41 GHz, respectively. Multiple rotational transitions were measured for this molecule in seven isotopic variants. K-ladder structure was clearly present in all of the spectra, indicating a molecule with C3v symmetry and a 1A1 ground electronic state. Extensive quadrupole hyperfine structure arising from the 67Zn nucleus was observed for the H67ZnCH3 species, suggesting covalent bonding to the zinc atom. From the multiple isotopic substitutions, a precise structure for HZnCH3 has been determined. The influence of the axial hydrogen atom slightly distorts the methyl group but stabilizes the Zn-C bond. This study suggests that HZnCH3 can be formed through the oxidative addition of zinc to methane in the gas phase under certain conditions. HZnCH3 is the first metal-methane insertion complex to be structurally characterized. © 2010 American Chemical Society.
• Halfen, D. T., & Ziurys, L. M. (2010). Millimeter/Submillimeter Velocity Modulation Spectroscopy of FeO+ (X 6+): Characterizing Metal Oxide Cations. Chem. Phys. Lett, 496, 8.
• Halfen, D. T., & Ziurys, L. M. (2010). Millimeter/submillimeter velocity modulation spectroscopy of FeO ⁺ (X⁶Σ⁺): Characterizing metal oxide cations. Chemical Physics Letters, 496(1-3), 8-13.
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  Abstract: The pure rotational spectrum of FeO+ (X 6Σ +) has been recorded using millimeter/submillimeter velocity modulation techniques, the first high-resolution measurement of a metal oxide cation. FeO+ was created in an AC discharge from Fe(CO)5 and N2O. Nine rotational transitions were recorded in the range 299-544 GHz, each consisting of six fine-structure components. The data were analyzed with a case (b) Hamiltonian, and rotational and spin parameters determined. The spin-spin constant suggests a low-lying 4Σ - excited state. The bond length established for FeO+, r0 = 1.641, is slightly longer than that of FeO, consistent with a covalent bonding scheme. © 2010 Elsevier B.V. All rights reserved.
• Halfen, D. T., & Ziurys, L. M. (2010). The submillimeter spectrum of AlD (X ¹Σ⁺). Astrophysical Journal Letters, 713(1), 520-523.
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  Abstract: The J = 2 ← 1 and 3 ← 2 rotational transitions of AlD (X 1Σ+) near 393 and 590 GHz have been measured using submillimeter direct absorption spectroscopy. AlD was created in an AC discharge of Al(CH3)3 and D2 in the presence of argon. This work is the first direct measurement of the J = 3 ← 2 transition of AlD. Each transition was found to be split into multiple hyperfine components due to the 27Al nuclear spin of I = 5/2, some of which are blended together. The data for AlD were fit with an effective Hamiltonian and rotational, electric quadrupole, and nuclear spin-rotation constants were determined for the molecule. The accuracy of these constants has been improved by a factor of 2-3, compared to previous studies. From these data, predictions for the J = 1 → 0 and 4 → 3 transitions of AlD have also been made. Photospheric AlH has been observed via its A 1Π-X 1Σ+ electronic transition, suggesting that this species may be present in circumstellar gas surrounding late-type stars, where four aluminum-bearing molecules have already been detected. High deuterium enrichment has been observed in hydride species in molecular clouds, making AlD a feasible candidate for searches in these objects as well. © 2010 The American Astronomical Society. All rights reserved.
• Lattanzi, V., Thorwirth, S., Halfen, D. T., Muck, L. A., Ziurys, L. M., Gauss, J., Thaddeus, P., & McCarthy, M. C. (2010). Bonding in the second-row analog of hydrogen cyanide: the curious case of bridged HPSi. Angew. Chem. Int. Ed.,, 49, 5661.
• Lattanzi, V., Thorwirth, S., Halfen, D. T., Mück, L. A., Ziurys, L. M., Thaddeus, P., Gauss, J., & McCarthy, M. C. (2010). Bonding in the heavy analogue of hydrogen cyanide: The curious case of bridged HPSi. Angewandte Chemie - International Edition, 49(33), 5661-5664.
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  PMID: 20818754;Abstract: chemical equation presented Curiouser and curiouser: By combining high-resolution molecular spectroscopy in the centimeter and millimeter wave regions, and high-level coupled-cluster quantum-chemical calculations, the structure of the HPSi molecule has been determined. The bridged geometry of HPSi is in remarkable contrast to that of the C and/or N analogues, such as HCN/ HNC, HCP, and HNSi, which are all linear. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
• Pulliam, R. L., & Ziurys, L. M. (2010). The pure rotational spectrum of the CrS radical in its X ⁵Π_r state. Journal of Chemical Physics, 133(17).
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  PMID: 21054038;Abstract: The pure rotational spectrum of the CrS radical has been measured in its ground X 5Πr state using gas-phase millimeter/ submillimeter direct absorption methods. The molecule was created by the reaction of chromium vapor, sublimed in a Broida-type oven, with hydrogen sulfide. Eleven rotational transitions were recorded for this free radical in the frequency range of 280-405 GHz; in most transitions, all five spin components were observed, and lambda-doubling was resolved in the Ω=0, 1, and 2 ladders. The data were fit with a Hund's case (a) Hamiltonian and rotational, spin-orbit, spin-spin, and lambda-doubling constants were established. Higher order spin and spin-orbit terms were essential in the analysis. The lambda-doubling constants indicate a nearby 5∑ + state at an energy of ∼1500-2000 cm-1. A bond length of 2.0781 Å was derived for CrS from the data, which is larger than the value of 2.0682 Å found for MnS by ∼0.01 Å. In contrast, the bond distance for MnO is greater than that of CrO by 0.03 Å, an illustration of the subtle differences between 3d oxide and sulfides. CrS is the second molecule in a 5Π state that has been studied by rotational spectroscopy. © 2010 American Institute of Physics.
• Pulliam, R. L., Savage, C., Agúndez, M., Cernicharo, J., Guélin, M., & Ziurys, L. M. (2010). Identification of KCN in IRC+10216: Evidence for selective cyanide chemistry. Astrophysical Journal Letters, 725(2 PART 2), L181-L185.
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  Abstract: A new interstellar molecule, KCN, has been identified toward the circumstellar envelope of the carbon-rich asymptotic giant branch star, IRC+10216 - the fifthmetal cyanide species to be detected in space. Fourteen rotational transitions of this T-shaped, asymmetric top were searched for in the frequency range of 83-250 GHz using the Arizona Radio Observatory (ARO) 12 m Kitt Peak antenna, the IRAM 30 m telescope, and the ARO Submillimeter Telescope. Distinct lines were measured for 10 of these transitions, including the K a = 1 and 2 asymmetry components of the J = 11→10 and J = 10→9 transitions, i.e., the K-ladder structure distinct to an asymmetric top. These data are some of themost sensitive astronomical spectra at λ∼1 and 3mmobtained to date, with 3σ noise levels ∼0.3 mK, made possible by new ALMA technology. The line profiles from the ARO and IRAM telescopes are consistent with a shell-like distribution for KCN with r outer ∼ 15″, but with an inner shell radius that extends into warmer gas. The column density for KCN in IRC+10216 was found to be N tot ≈ 1.0×1012 cm-2 with a rotational temperature of Trot ∼ 53 K. The fractional abundance was calculated to be f(KCN/H2) ∼ 6×10-10, comparable to that of KCl. The presence of KCN in IRC+10216, along with MgNC, MgCN, NaCN, and AlNC, suggests that cyanide/isocyanide species are the most common metal-containing molecules in carbon-rich circumstellar gas. © 2010. The American Astronomical Society. All rights reserved.
• Pulliam, R. L., Zack, L. N., & Ziurys, L. M. (2010). The pure rotational spectrum of TiS (X³Δ_r) at submillimeter wavelengths. Journal of Molecular Spectroscopy, 264(1), 50-54.
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  Abstract: The pure rotational spectrum of TiS in its X3Δr ground state has been measured using millimeter-wave direct-absorption techniques in the frequency range of 313-425 GHz. This free radical was created by the reaction of titanium vapor, produced in a high-temperature Broida-type oven, with H2S. Eight to ten rotational transitions were recorded for the main titanium isotopologue, 48TiS, in the v = 0 and v = 1 levels, as well as for the v = 0 state of 46TiS, observed in natural abundance (48Ti:46Ti = 74:8). All three Ω components were observed in almost every recorded transition, with no evidence for lambda-doubling. The data were fit with a Hund's case(a) Hamiltonian, and rotational, spin-orbit, and spin-spin constants were determined, as well as equilibrium parameters for 48TiS. Relatively few fine structure parameters were needed for the analysis of TiS (A, AD, and λ), unlike other 3d metal species. The rotational pattern of the three fine structure components suggests the presence of a nearby excited 1Δ state, lying ∼3000 cm-1 higher in energy. From the equilibrium parameters, the dissociation energy for TiS was estimated to be ∼5.1 eV, in reasonable agreement with past thermochemical data. © 2010 Elsevier Inc. All rights reserved.
• Sun, M., Halfen, D. T., Min, J., Harris, B., Clouthier, D. J., & Ziurys, L. M. (2010). The rotational spectrum of CuCCH (X̃ ¹∑⁺): A Fourier transform microwave discharge assisted laser ablation spectroscopy and millimeter/submillimeter study. Journal of Chemical Physics, 133(17).
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  PMID: 21054026;Abstract: The pure rotational spectrum of CuCCH in its ground electronic state (X̃ 1∑+) has been measured in the frequency range of 7-305 GHz using Fourier transform microwave (FTMW) and direct absorption millimeter/submillimeter methods. This work is the first spectroscopic study of CuCCH, a model system for copper acetylides. The molecule was synthesized using a new technique, discharge assisted laser ablation spectroscopy (DALAS). Four to five rotational transitions were measured for this species in six isotopologues (63CuCCH, 65CuCCH, 63Cu 13CCH, 63Cu 13CH, 63Cu 13CCH, and 63CuCCD); hyperfine interactions arising from the copper nucleus were resolved, as well as smaller splittings in CuCCD due to deuterium quadrupole coupling. Five rotational transitions were also recorded in the millimeter region for 63CuCCH and 65CuCCH, using a Broida oven source. The combined FTMW and millimeter spectra were analyzed with an effective Hamiltonian, and rotational, electric quadrupole (Cu and D) and copper nuclear spin-rotation constants were determined. From the rotational constants, an rm2 structure for CuCCH was established, with r Cu-C =1.8177 (6) Å, rC-C =1.2174 (6) Å, and rC-H =1.046 (2) Å. The geometry suggests that CuCCH is primarily a covalent species with the copper atom singly bonded to the CCH moiety. The copper quadrupole constant indicates that the bonding orbital of this atom may be sp hybridized. The DALAS technique promises to be fruitful in the study of other small, metal-containing molecules of chemical interest. © 2010 American Institute of Physics.
• Tenenbaum, E. D., & Ziurys, L. M. (2010). Exotic metal molecules in oxygen-rich envelopes: Detection of ALOH (X ¹Σ⁺) in VY Canis Majoris. Astrophysical Journal Letters, 712(1 PART 2), L93-L97.
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  Abstract: A new interstellar molecule, AlOH, has been detected toward the envelope of VY Canis Majoris (VY CMa), an oxygen-rich red supergiant. Three rotational transitions of AlOH were observed using the facilities of the Arizona Radio Observatory (ARO). The J = 9 → 8 and J = 7 → 6 lines at 1mm were measured with the ARO Submillimeter Telescope, while the J = 5 → 4 transition at 2mm was observed with the ARO 12m antenna on Kitt Peak. The AlOH spectra exhibit quite narrow line widths of 16-23kms-1, as found for NaCl in this source, indicating that the emission arises from within the dust acceleration zone of the central circumstellar outflow. From a radiative transfer analysis, the abundance of AlOH relative to H2 was found to be 1 × 10-7 for a source size of 0.26″ or 22 R * . In contrast, AlCl was not detected with f ≤ 5 × 10-8. AlOH is likely formed just beyond the photosphere via thermodynamic equilibrium chemistry and then disappears due to dust condensation. The AlOH/AlO abundance ratio found in VY CMa is 17. Therefore, AlOH appears to be the dominant gas-phase molecular carrier of aluminum in this oxygen-rich shell. Local thermodynamic equilibrium calculations predict that the monohydroxides should be the major carriers of Al, Ca, and Mg in O-rich envelopes, as opposed to the oxides or halides. The apparent predominance of aluminum-bearing molecules in VY CMa may reflect proton addition processes in H-shell burning. © 2010 The American Astronomical Society.
• Tenenbaum, E. D., Dodd, J. L., Milam, S. N., Woolf, N. J., & Ziurys, L. M. (2010). Comparative spectra of oxygen-rich versus carbon-rich circumstellar shells: VY canis majoris and IRC +10216 at 215-285 GHZ. Astrophysical Journal Letters, 720(1 PART 2), L102-L107.
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  Abstract: Asensitive (1σ rms at 1 MHz resolution∼3 mK) 1mmspectral line survey (214.5-285.5 GHz) ofVYCanisMajoris (VY CMa) and IRC +10216 has been conducted to compare the chemistries of oxygen- and carbon-rich circumstellar envelopes. This study was carried out using the Submillimeter Telescope of the Arizona Radio Observatory with a new Atacama Large Millimeter Array type receiver. This survey is the first to chemically characterize an O-rich circumstellar shell at millimeter wavelengths. In VY CMa, 128 emission features were detected arising from 18 different molecules; and in IRC +10216, 720 lines were observed, assigned to 32 different species. The 1 mm spectrum of VY CMa is dominated by SO2 and SiS; in IRC +10216, C4H and SiC 2 are the most recurrent species. Ten molecules were common to both sources: CO, SiS, SiO, CS, CN, HCN, HNC, NaCl, PN, and HCO+. Sulfur plays an important role in VY CMa, but saturated/unsaturated carbon dominates the molecular content of IRC +10216, producing CH2NH, for example. Although the molecular complexity of IRC +10216 is greater, VY CMa supports a unique "inorganic" chemistry leading to the oxides PO, AlO, and AlOH. Only diatomic and triatomic compounds were observed in VY CMa, while species with four or more atoms are common in IRC +10216, reflecting carbon's ability to form multiple strong bonds, unlike oxygen. In VY CMa, a new water maser (v2 = 2) has been found, as well as vibrationally excitedNaCl. Toward IRC +10216, vibrationally excited CCHwas detected for the first time. © 2010. The American Astronomical Society. All rights reserved.
• Tenenbaum, E. D., Dodd, J. L., Milam, S. N., Woolf, N. J., & Ziurys, L. M. (2010). The Arizona Radio Observatory 1 mm spectral survey of IRC +10216 and VY Canis Majoris (215-285 GHz). Astrophysical Journal, Supplement Series, 190(2), 348-417.
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  Abstract: A low noise (1σ rms ∼ 3 mK) 1 mm spectral survey (214.5-285.5 GHz) of the oxygen-rich supergiant VY Canis Majoris and the carbon-rich asymptotic giant branch star IRC +10216 has been conducted using the Arizona Radio Observatory's 10 m Submillimeter Telescope. Here the complete data set is presented. This study, carried out with a new ALMA-type receiver, marks the first continuous band scan of an O-rich circumstellar envelope, and the most sensitive survey to date of IRC +10216. In VY CMa, 130 distinct molecular lines were detected, 14 of which cannot be identified; in IRC +10216, 717 lines were observed, with 126 features remaining unidentified. In the 1 mm bands of VY CMa and IRC +10216, emission is present from 18 and 32 different chemical compounds, respectively, with 10 species common to both sources. Many narrow emission lines were observed in both circumstellar shells, arising from vibrationally excited molecules and from refractory-containing species. Line profiles in VY CMa also exhibit a variety of different shapes, caused by the complex, asymmetric outflow of this object. The survey highlights the fact that C-rich and O-rich circumstellar envelopes are chemically interesting, and both are sources of new interstellar molecules. The high number of unidentified lines and the unreliable rest frequencies for known species such as NaCN indicate the need for additional laboratory spectroscopy studies. © 2010. The American Astronomical Society. All rights reserved.
• DiSanti, M. A., Villanueva, G. L., Milam, S. N., Zack, L. N., Bonev, B. P., Mumma, M. J., Ziurys, L. M., & Anderson, W. M. (2009). A multi-wavelength study of parent volatile abundances in Comet C/2006 M4 (SWAN). Icarus, 203(2), 589-598.
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  Abstract: Volatile organic emissions were detected post-perihelion in the long-period Comet C/2006 M4 (SWAN) in October and November 2006. Our study combines target-of-opportunity infrared observations using the Cryogenic Echelle Spectrometer (CSHELL) at the NASA-IRTF 3-m telescope, and millimeter wavelength observations using the Arizona Radio Observatory (ARO) 12-m telescope. Five parent volatiles were measured with CSHELL (H2O, CO, CH3OH, CH4, and C2H6), and two additional species (HCN and CS) were measured with the ARO 12-m. These revealed highly depleted CO and somewhat enriched CH3OH compared with abundances observed in the dominant group of long-period (Oort cloud) comets in our sample and similar to those observed recently in Comet 8P/Tuttle. This may indicate highly efficient H-atom addition to CO at very low temperature (∼10-20 K) on the surfaces of interstellar (pre-cometary) grains. Comet C/2006 M4 had nearly "normal" C2H6 and CH4, suggesting a processing history similar to that experienced by the dominant group. When compared with estimated water production at the time of the millimeter observations, HCN was slightly depleted compared with the normal abundance in comets based on IR observations but was consistent with the majority of values from the millimeter. The ratio CS/HCN in C/2006 M4 was within the range measured in ten comets at millimeter wavelengths. The higher apparent H-atom conversion efficiency compared with most comets may indicate that the icy grains incorporated into C/2006 M4 were exposed to higher H-atom densities, or alternatively to similar densities but for a longer period of time. © 2009 Elsevier Inc. All rights reserved.
• Halfen, D. T., & Ziurys, L. M. (2009). Millimeter/submillimeter-wave spectrum of the VCl⁺ radical in its X ⁴Σ^- ground state. Journal of Physical Chemistry A, 113(47), 13436-13442.
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  PMID: 19921948;Abstract: The pure rotational spectrum of the molecular ion VCl+ (X 4Σ-) has been recorded from 274 to 419 GHz using a combination of millimeter direct absorption and velocity modulation spectroscopy. This study is the first spectroscopic measurement of this species in the laboratory, which has also enabled the determination of the ground state term, 4Σ-. VCl+ was produced in an AC discharge of VCl4 and argon. Fifteen and eleven rotational transitions were recorded for the V35Cl+ and V 37Cl+ isotopologues, respectively. The fine structure splittings of the 4Σ- state were found to deviate significantly from a case (b) pattern. Specifically, spin components from adjacent rotational transitions were found to overlap in frequency. Unusual vanadium hyperfine splittings were also observed in the VCl+ spectra; the expected vanadium octet was clearly present for the F2 and F3 spin components but was partially collapsed and reversed in frequency ordering in the F1 and F4 cases. The data were analyzed in a global fit, and rotational, fine structure, and hyperfine constants were determined. For VCl+, the values of both the spin-spin and spin-rotation parameters are extremely large, as were the third-order hyperfine and spin-rotation terms, bs and γs. For example, the spin-spin constant is a = 417 900(22 700) MHz, while γ = 6567(51) MHz. The values of these constants indicate a high density of excited electronic states close to the ground state, which contribute to second and third-order spin-orbit coupling. The hyperfine constants suggest a s1p2 electron configuration, as opposed to s1d2, as found in VS and VO. The bond length of VCl+, r0 = 2.119(2) Å, is shorter than that of VCl by 0.1 Å, which has r0 = 2.219 Å. The decrease in bond length is attributed to an increase in the electrostatic attraction between V2+ and Cl-, as opposed to V+ and Cl - for VCl. © 2009 American Chemical Society.
• Halfen, D. T., & Ziurys, L. M. (2009). The Millimeter/Submillimeter-wave Spectrum of the VCl+ Radical (X 4),”. J. Phys. Chem. A, Robert W. Field Festschrift Issue, 113(13436).
• Halfen, D. T., Sun, M., Clouthier, D. J., & Ziurys, L. M. (2009). The rotational spectrum of the CCP (X² Π_r) radical and its ¹³C isotopologues at microwave, millimeter, and submillimeter wavelengths. Journal of Chemical Physics, 130(1).
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  PMID: 19140613;Abstract: The pure rotational spectrum of CCP (X Πr2) has been measured at microwave, millimeter, and submillimeter wavelengths (17-545 GHz), along with its C13 isotopologues (C13 C13 P, C C13 P, and C13 CP). The spectra of these species were recorded using a combination of millimeter/submillimeter direct absorption methods and Fourier transform microwave (FTMW) techniques. The phosphorus dicarbides were created in the gas phase from the reaction of red phosphorus and acetylene or methane in argon in an ac discharge for the direct absorption experiments, and using P Cl3 as the phosphorus source in a pulsed dc nozzle discharge for the FTMW measurements. A total of 35 rotational transitions were recorded for the main isotopologue, and between 2 and 8 for the C13 - substituted species. Both spin-orbit components were identified for CCP, while only the =12 ladder was observed for C13 C13 P, C C13 P, and C13 CP. Hyperfine splittings due to phosphorus were observed for each species, as well as carbon-13 hyperfine structure for each of the C13 - substituted isotopologues. The data were fitted with a Hund's case (a) Hamiltonian, and rotational, fine structure, and hyperfine parameters were determined for each species. The rm (1) bond lengths established for CCP, r (C-C) =1.289 (1) Å and r (C-P) =1.621 (1) Å, imply that there are double bonds between both the two carbon atoms and the carbon and phosphorus atoms. The hyperfine constants suggest that the unpaired electron in this radical is primarily located on the phosphorus nucleus, but with some electron density also on the terminal carbon atom. There appears to be a minor resonance structure where the unpaired electron is on the nucleus of the end carbon. The multiple double bond structure forces the molecule to be linear, as opposed to other main group dicarbides, such as Si C2, which have cyclic geometries. © 2009 American Institute of Physics.
• Halfen, D. T., Ziurys, L. M., & Brown, J. M. (2009). Fine structure and hyperfine perturbations in the pure rotational spectrum of the VCl radical in its X⁵ Δ r state. Journal of Chemical Physics, 130(16).
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  PMID: 19405573;Abstract: The pure rotational spectrum of the VCl radical in its 5Δ r ground state has been recorded in the range 236-417 GHz using millimeter/submillimeter direct absorption techniques. This species was created in an ac discharge of VCl4 and argon. Ten rotational transitions of V35 Cl were measured in all five Ω ladders; an additional nine transitions of the Ω=1 spin state were recorded in order to evaluate the 51V hyperfine structure. Hyperfine interactions associated with the C 35 l nucleus were not resolved, consistent with the ionic structure of the molecule. Because of extensive perturbations caused by the low-lying A Π5 r excited state, the rotational spectrum of the ground state has been found to be quite irregular. The four lowest Ω ladders exhibit unusually large lambda-doubling interactions, with the Ω=1 component showing the largest splitting, over 2 GHz in magnitude. The Ω=1 transitions are also shifted to higher frequency relative to the other spin components. In addition, the hyperfine structure varies widely between the Ω ladders, and an avoided crossing is observed in two transitions of both the Ω=1e and 2e components. The data have been analyzed with a case (c) Hamiltonian, and effective rotational, lambda-doubling, and hyperfine constants have been determined for V35 Cl. Higher-order parity-dependent magnetic hyperfine terms dΔ2 and dΔ3 were required in the analysis, derived from perturbation theory, in addition to the usual dΔ parameter. The local perturbations evident in these spectra indicate that the A Π5 r excited state lies within the spin-orbit manifold of the ground state, well below the predicted value of 517 cm-1. Mixing of the A Π5 r and X 5Δ r states apparently causes both local and global perturbations in the ground state spectrum. © 2009 American Institute of Physics.
• Halfen, D. T., Ziurys, L. M., Brünken, S., Gottlieb, C. A., McCarthy, M. C., & Thaddeus, P. (2009). Detection of a new interstellar molecule: Thiocyanic acid HSCN. Astrophysical Journal Letters, 702(2 PART 2), L124-L127.
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  Abstract: A new interstellar molecule, HSCN (thiocyanic acid), an energetic isomer of the well-known species HNCS, has been detected toward Sgr B2(N) with the Arizona Radio Observatory 12 m telescope. Eight rotational transitions in the Ka = 0 ladder were observed in the 2 mm and 3 mm bands. Five consecutive transitions in the 3 mm band are unblended, but three in the 2 mm band are partially masked by lines of other molecules. The peak intensity of all eight transitions are well described by a rotational temperature that is in very good agreement with that of many other molecules in this source. The line width and radial velocity of HSCN match closely with those of the ground state isomer HNCS (isothiocyanic acid), HNCO (isocyanic acid), and HOCN (cyanic acid); preliminary maps indicate that all four molecules are similarly distributed in Sgr B2. Although HSCN is calculated to lie over 3000 K higher in energy than HNCS, its column density of 1.3 × 1013 cm-2 in Sgr B2(N) is only three times lower than that of HNCS. The fractional abundances of HSCN and HNCS relative to H2 are 4.5 × 10-12 and 1.1 × 10-11. By analogy with the isomeric pair HCN and HNC, these two sulfur-bearing isomers are plausibly formed from a common cation precursor. © 2009. The American Astronomical Society.
• Milam, S. N., Woolf, N. J., & Ziurys, L. M. (2009). Circumstellar ¹²C/¹³C isotope ratios from millimeter observations of CN and CO: Mixing in carbon- and oxygen-rich stars. Astrophysical Journal Letters, 690(1), 837-849.
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  Abstract: A survey of the 12C/13C ratio toward circumstellar envelopes has been conducted at millimeter wavelengths using the facilities of the Arizona Radio Observatory (ARO). The ratios were obtained for a sample of local C- and O-rich asymptotic giant branch and supergiant stars from observations of the 12C and 13C isotopologues of CO and CN, respectively. The J = 1 → 0 transitions of both molecules were observed at λ = 3 mm using the ARO 12 m telescope, while the J = 2 → 1 lines of the two species were measured using the ARO Sub-Millimeter Telescope (SMT) at λ = 1 mm. The 12C/13C ratios were determined from the CO data by modeling both transitions simultaneously with a circumstellar radiative transfer code, which can account for the high opacities present in the emission from this species. In the case of CN, the hyperfine structure was used to evaluate opacity effects. Ratios obtained independently from CO and CN are in good agreement. For the C-rich envelopes, the ratios fall in the range 12C/13C 25-90, while the O-rich shells have values of 10-35. Ratios of 12C/13C 3-14 are found for the supergiant stars, with the exception of VY CMa, where the values lie in the range 25-46. All ratios obtained in this study are ≤ 89, the solar value, suggesting that substantial carbon-13 enrichment may be currently occurring in the local interstellar medium. A qualitative model was constructed based on first and third dredge-up convective mixing that can reproduce the observed ratios. Substantial mixing of H-burning products must occur to explain the ratios in the O-rich objects, while a wide range of 12C/ 13C values can be generated by only a few percent mixing of He-burning ashes in the C-rich case. The 12C/13C ratios obtained in this study should help improve stellar yield models and contribute to the understanding of Galactic chemical evolution. © 2009. The American Astronomical Society. All rights reserved.
• Pulliam, R. L., Sun, M., Flory, M. A., & Ziurys, L. M. (2009). The sub-millimeter and Fourier transform microwave spectrum of HZnCl (X ¹Σ⁺). Journal of Molecular Spectroscopy, 257(2), 128-132.
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  Abstract: The pure rotational spectrum of HZnCl (X 1Σ+) has been recorded using sub-millimeter direct-absorption methods in the range of 439-540 GHz and Fourier transform microwave (FTMW) techniques from 9 to 39 GHz. This species was produced by the reaction of zinc vapor and chlorine gas with H2 or D2 in a d.c. glow discharge for the sub-millimeter studies. In the FTMW measurements, HZnCl was created in a discharge nozzle from Cl2 and (CH3)2Zn. Between 5 and 10 rotational transitions were measured in the sub-millimeter regime for four zinc and two chlorine isotopologues; four transitions were recorded with the FTMW machine for the main isotopologue, each consisting of several chlorine hyperfine components. The data are consistent with a linear molecule and a 1Σ+ ground electronic state. Rotational and chlorine quadrupole constants were established from the spectra, as well as an rm(2) structure. The Zn-Cl and Zn-H bond lengths were determined to be 2.0829 and 1.5050 Å, respectively; in contrast, the Zn-Cl bond distance in ZnCl is 2.1300 Å, longer by ∼0.050 Å. The zinc-chlorine bond distance therefore shortens with the addition of the H atom. The 35Cl electric quadrupole coupling constant of eQq = -27.429 MHz found for HZnCl suggests that this molecule is primarily an ionic species with some covalent character for the Zn-Cl bond. © 2009 Elsevier Inc. All rights reserved.
• Sun, M., Apponi, A. J., & Ziurys, L. M. (2009). Fourier transform microwave spectroscopy of HZnCN (X ¹Σ ⁺) and ZnCN (X ²Σ⁺). Journal of Chemical Physics, 130(3).
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  PMID: 19173523;Abstract: The pure rotational spectrum of HZnCN in its X 1Σ + + electronic state has been recorded using pulsed Fourier transform microwave (FTMW) techniques in the frequency range 7-39 GHz-the first spectroscopic study of this species in the gas phase. The FTMW spectrum of ZnCN (X 2Σ+) has been measured as well. A new FTMW spectrometer with an angled beam and simplified electronics, based on a cryopump, was employed for these experiments. The molecules were created in a dc discharge from a gas mixture of Zn (CH3) 2 and cyanogen (1% D2 for the deuterated analogs), diluted with argon, that was expanded supersonically from a pulsed nozzle. Seven isotopologues of HZnCN arising from zinc, deuterium, and C 13 substitutions were studied; for every species, between three and five rotational transitions were recorded, each consisting of numerous hyperfine components arising from nitrogen, and in certain cases, deuterium, and 67-zinc nuclear spins. Four transitions of ZnCN were measured. From these data, rotational, nuclear spin-rotation, and quadrupole coupling constants have been determined for HZnCN, as well as rotational, and magnetic and quadrupole hyperfine parameters for the ZnCN radical. The bond lengths determined for HZnCN are rH-Zn =1.495 Å, rZn-C =1.897 Å, and rC-N =1.146 Å, while those for ZnCN are rZn-C =1.950 Å and rC-N =1.142 Å. The zinc-carbon bond length thus shortens with the addition of the H atom. The nitrogen quadrupole coupling constant eqQ was found to be virtually identical in both cyanide species (-5.089 and -4.931 MHz), suggesting that the electric field gradient across the N nucleus is not influenced by the H atom. The quadrupole constant for the Z 67 n nucleus in H Z 67 nCN is unusually large relative to that in Z 67 nF (-104.578 versus -60 MHz), evidence that the bonding in the cyanide has more covalent character than in the fluoride. This study additionally suggests that hydrides of other metal cyanide species are likely candidates for high resolution spectroscopic investigations. © 2009 American Institute of Physics.
• Sun, M., Clouthier, D. J., & Ziurys, L. M. (2009). The Fourier transform microwave spectrum of the arsenic dicarbide radical (CCAs: X̃²Π_1/2) and its ¹³C isotopologues. Journal of Chemical Physics, 131(22).
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  PMID: 20001046;Abstract: The pure rotational spectrum of the CCAs radical in its ground electronic and spin state, X̃2Π1/2, has been measured using Fourier transform microwave techniques in the frequency range of 12-40 GHz. This species was created in a supersonic expansion from a reaction mixture of AsCl3 and C2H2 or CH4 diluted in high pressure argon, using a pulsed nozzle containing a dc discharge source. Three rotational transitions were measured for the main isotopologue, 12C12CAs, in the ω=1/2 ladder; both lambda-doubling and arsenic (I=3/2) hyperfine interactions were observed in these spectra. In addition, two to four rotational transitions were recorded for the 13C13CAs, 13C12CAs, and 12C13CAs species. In these three isotopologues, hyperfine splittings were also resolved arising from the 13C nuclei (I=1/2), creating complex spectral patterns. The CCAs spectra were analyzed with a case (a) Hamiltonian, and effective rotational, lambda-doubling, and arsenic and carbon-13 hyperfine constants were determined for the ω=1/2 ladder. From the effective rotational constants of the four isotopologues, an r m(1) structure has been derived with rC-C=1.287 Å and rC-As=1.745 Å. These bond lengths indicate that the predominant structure for arsenic dicarbide is C=C=As·, with some contributing C≡C and C≡As triple bond characters. The hyperfine constants established in this work indicate that about 2/3 of the unpaired electron density lies on the arsenic atom, with the remaining percentage on the terminal carbon. The value of the arsenic quadrupole coupling constant (eqQ=-202 MHz) suggests that the As-C bond has a mixture of covalent and ionic characters, consistent with theoretical predictions that both π backbonding and electron transfer play a role in creating a linear, as opposed to a cyclic, structure for certain heteroatom dicarbides. © 2009 American Institute of Physics.
• Tenenbaum, E. D., & Ziurys, L. M. (2009). Millimeter detection of alo (X ²Σ⁺): Metal oxide chemistry in the envelope of VY canis majoris. Astrophysical Journal Letters, 694(1), L59-L63.
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  Abstract: A new circumstellar molecule, the radical AlO (X 2Σ +), has been detected toward the envelope of the oxygen-rich supergiant star VY Canis Majoris (VY CMa) using the Arizona Radio Observatory (ARO). The N = 7 → 6 and 6 → 5 rotational transitions of AlO at 268 and 230 GHz were observed at 1 mm using the ARO Submillimeter Telescope (SMT) and the N = 4 → 3 line was detected at 2 mm using the ARO 12 m telescope. Based on the shape of the line profiles, AlO most likely arises from the dust-forming region in the spherical outflow of VY CMa, as opposed to the blue or redshifted winds, with a source size of θ s 05. Given this source size, the column density of AlO was found to be N tot 2 × 1015 cm-2 for T rot 230 K, with a fractional abundance, relative to H2, of 10-8. Gas-phase thermodynamic equilibrium chemistry is the likely formation mechanism for AlO in VY CMa, but either shocks disrupt the condensation process into Al 2O3, or chemical "freezeout" occurs. The species therefore survives further into the circumstellar envelope to a radius of r 20 R *. The detection of AlO in VY CMa is additional evidence of an active gas-phase refractory chemistry in oxygen-rich envelopes, and suggests such objects may be fruitful sources for other new oxide identifications. © 2009. The American Astronomical Society. All rights reserved..
• Tenenbaum, E. D., Milam, S. N., Woolf, N. J., & Ziurys, L. M. (2009). Molecular survival in evolved planetary nebulae: Detection of H ₂CO, c-C₃H₂, and C₂H in the helix. Astrophysical Journal Letters, 704(2 PART 2), L108-L112.
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  Abstract: H2CO, c-C3H2, and C2H have been identified in the neutral envelope of the highly evolved planetary nebula (PN), the Helix (also know as NGC 7293). Emission from these species were detected toward a peak position in CO, 372″ east of the central star, using the facilities of the Arizona Radio Observatory (ARO). C2H and c-C 3H2 were identified on the basis of their 3 mm transitions, measured with the ARO 12 m, while five lines of H2CO were observed using the 12 m at 2 and 3 mm and the ARO Submillimeter Telescope at 1 mm. From a radiative transfer analysis of the formaldehyde emission, the molecular material was determined to have a density of n(H2) ∼3 × 105 cm-3, with a kinetic temperature of T kin ∼20 K. Column densities for C2H, H2CO, and c-C3H2 of Ntot ∼1.4 × 10 13 cm-2, 1.1 × 1012 cm-2, and 3 × 1011 cm-2, respectively, were derived, corresponding to fractional abundances relative to H2 of f (H 2CO) = 1 × 10-7, f (c-C3H2) = 3 × 10-8, and f (C2H) = 1 × 10-6. The physical conditions found support the notion that molecules in evolved PNe survive in dense clumps in pressure equilibrium, shielded from photodissociation. The presence of H2CO, c-C3H 2, and C2H, along with the previously observed species CN, HNC, HCN, and HCO+, indicates that a relatively complex chemistry can occur in the late stages of PN evolution, despite potentially destructive ultraviolet radiation. These molecules have also been observed in diffuse clouds, suggesting a possible connection between molecular material in evolved PNe and the diffuse ISM. © 2009 The American Astronomical Society. All rights reserved.
• Zack, L. N., & Ziurys, L. M. (2009). The pure rotational spectrum of ZnS (X¹Σ⁺). Journal of Molecular Spectroscopy, 257(2), 213-216.
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  Abstract: The pure rotational spectrum of ZnS (X1Σ+) has been measured using direct-absorption millimeter/sub-millimeter techniques in the frequency range 372-471 GHz. This study is the first spectroscopic investigation of this molecule. Spectra originating in four zinc isotopologues (64ZnS, 66ZnS, 68ZnS, and 67ZnS) were recorded in natural abundance in the ground vibrational state, and data from the v = 1 state were also measured for the two most abundant zinc species. Spectroscopic constants have been subsequently determined, and equilibrium parameters have been estimated. The equilibrium bond length was calculated to be re ∼ 2.0464 Å, which agrees well with theoretical predictions. In contrast, the dissociation energy of DE ∼ 3.12 eV calculated for ZnS, assuming a Morse potential, was significantly higher than past experimental and theoretical estimates, suggesting diabatic interaction with other potentials that lower the effective dissociation energy. Although ZnS is isovalent with ZnO, there appear to be subtle differences in bonding between the two species, as suggested by their respective force constants and bond length trends in the 3d series. © 2009 Elsevier Inc. All rights reserved.
• Zack, L. N., Pulliam, R. L., & Ziurys, L. M. (2009). The pure rotational spectrum of ZnO in the X¹Σ⁺ and a³Π_i states. Journal of Molecular Spectroscopy, 256(2), 186-191.
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  Abstract: The pure rotational spectrum of ZnO has been measured in its ground X1Σ+ and excited a3Πi states using direct-absorption methods in the frequency range 239-514 GHz. This molecule was synthesized by reacting zinc vapor, generated in a Broida-type oven, with N2O under DC discharge conditions. In the X1Σ+ state, five to eight rotational transitions were recorded for each of the five isotopologues of this species (64ZnO, 66ZnO, 67ZnO, 68ZnO, and 70ZnO) in the ground and several vibrational states (v = 1-4). Transitions for three isotopologues (64ZnO, 66ZnO, and 68ZnO) were measured in the a3Πi state for the v = 0 level, as well as from the v = 1 state of the main isotopologue. All three spin-orbit components were observed in the a3Πi state, each exhibiting splittings due to lambda-doubling. Rotational constants were determined for the X1Σ+ state of zinc oxide. The a3Πi state data were fit with a Hund's case (a) Hamiltonian, and rotational, spin-orbit, spin-spin, and lambda-doubling constants were established. Equilibrium parameters were also determined for both states. The equilibrium bond length determined for ZnO in the X1Σ+ state is 1.7047 Å, and it increases to 1.8436 Å for the a excited state, consistent with a change from a π4 to a π3σ1 configuration. The estimated vibrational constants of ωe ∼ 738 and 562 cm-1 for the ground and a state agreed well with prior theoretical and experimental investigations; however, the estimated dissociation energy of 2.02 eV for the a3Πi state is significantly higher than previous predictions. The lambda-doubling constants suggest a low-lying 3Σ state. © 2009 Elsevier Inc. All rights reserved.
• Agúndez, M., Cernicharo, J., Pardo, J. R., Expósito, J. F., Guélin, M., Tenenbaum, E. D., Ziurys, L. M., & Apponi, A. J. (2008). Understanding the chemical complexity in Circumstellar Envelopes of C-Rich AGB stars: The case of IRC +10216. Astrophysics and Space Science, 313(1-3), 229-233.
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  Abstract: The circumstellar envelopes of carbon-rich AGB stars show a chemical complexity that is exemplified by the prototypical object IRC +10216, in which about 60 different molecules have been detected to date. Most of these species are carbon chains of the type C n H, C n H2, C n N, HC n N. We present the detection of new species (CH2CHCN, CH2CN, H2CS, CH3CCH and C3O) achieved thanks to the systematic observation of the full 3 mm window with the IRAM 30m telescope plus some ARO 12m observations. All these species, known to exist in the interstellar medium, are detected for the first time in a circumstellar envelope around an AGB star. These five molecules are most likely formed in the outer expanding envelope rather than in the stellar photosphere. A pure gas phase chemical model of the circumstellar envelope is reasonably successful in explaining the derived abundances, and additionally allows to elucidate the chemical formation routes and to predict the spatial distribution of the detected species. © 2007 Springer Science+Business Media B.V.
• Apponi, A. J., Sun, M., Halfen, D. T., Ziurys, L. M., & Müller, H. (2008). The rotational spectrum of anti-ethylamine (CH₃CH ₂NH₂) from 10 to 270 GHz: A laboratory study and astronomical search in SGR B2(N). Astrophysical Journal, 673(2), 1240-1248.
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  Abstract: The pure rotational spectrum of the lowest energy (anti-) conformer of ethylamine (CH3CH2NH3) has been measured in the frequency range of 10-270 GHz. The spectrum was recorded using both millimeter-wave absorption spectroscopy and Fourier transform microwave (FTMW) techniques. Ten rotational transitions of this molecule were recorded in the frequency range of 10-40 GHz using FTMW methods, resulting in the assignment of 53 quadrupoleresolved hyperfine lines; in the millimeter-wave region (48-270 GHz), nearly 600 transitions were assigned to the ground (anti-) state. The amine group in CH3CH2NH2 undergoes inversion, resulting in a doubling that is frequently small and most apparent in the low-frequency K-doubling transitions. In addition, seemingly random rotational levels of this molecule were found to be significantly perturbed. The cause of these perturbations is presently uncertain, but torsion-rotation interactions with the higher lying gauche conformers seem to be a likely explanation. An astronomical search was conducted for ethylamine toward Sgr B2(N) using the Kitt Peak 12 m antenna and the Sub-Millimeter Telescope (SMT) of the Arizona Radio Observatory. Frequencies of 70 favorable rotational transitions were observed in this search, which covered the range 68-263 GHz. Ethylamine was not conclusively detected in Sgr B2(N), with an upper limit to the column density of (1-8) × 1013 cm with/(CH3CH2NH 2/H2) ∼ (0.3-3) × 1011, assuming a rotational temperature of 50-220 K. These observations indicate a gas-phase CH3 CH2NH2/CH3NH2 ratio of
• Flory, M. A., & Ziurys, L. M. (2008). Submillimeter-wave spectroscopy of VN (X³Δ_r) and VO (X⁴Σ^-): A study of the hyperfine interactions. Journal of Molecular Spectroscopy, 247(1), 76-84.
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  Abstract: The pure rotational spectra of VN (X3Δr) and VO (X4Σ-) have been recorded in the frequency range 290-520 GHz using direct absorption spectroscopy. These radicals were synthesized in the gas-phase from the reaction of VCl4 with either N2 or H2O in an AC discharge. Seven rotational transitions were recorded for each molecule; in both sets of spectra, fine and hyperfine structures were resolved. The data sets for VN and VO were fit with Hund's case (a) and case (b) Hamiltonians, respectively, and rotational, fine structure, and hyperfine constants determined. For VN, however, an additional hyperfine parameter, Δa, was necessary for the analysis of the Ω = 2 sublevel to account for perturbations from a nearby 1Δ state, in addition to the usual Frosch and Foley constants. Determination of Δa suggests that the 1Δ state lies ∼3000 cm-1 above the ground state. In VO, the hyperfine structure in the F2 and F3 components was found to become heavily mixed due to an avoided crossing, predicted by previous optical studies to be near the N = 15 level. The hyperfine constants established for these two molecules are consistent with the proposed σ1δ1 and σ1δ2 electron configurations. © 2007 Elsevier Inc. All rights reserved.
• Fuhrmann, L., Krichbaum, T. P., Witzel, A., Kraus, A., Britzen, S., Bernhart, S., Impellizzeri, C. M., Agudo, I., Klare, J., Sohn, B. W., Angelakis, E., Bach, U., Gabányi, K., Körding, E., Pagels, A., Zensus, J. A., Wagner, S. J., Ostorero, L., Ungerechts, H., , Grewing, M., et al. (2008). Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71. Astronomy and Astrophysics, 490(3), 1019-1037.
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  Abstract: Aims. The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent brightness temperatures. Methods. The observing campaign involved simultaneous ground-based monitoring at radio to IR/optical wavelengths and was centered around a 500-ks pointing with the INTEGRAL satellite (November 10-17, 2003). Here, we present the combined analysis and results of the radio observations, covering the cm- to sub-mm bands. This facilitates a detailed study of the variability characteristics of an inter- to intra-day variable IDV source from cm- to the short mm-bands. We further aim to constrain the variability brightness temperatures (TB) and Doppler factors (∂) comparing the radio-bands with the hard X-ray emission, as seen by INTEGRAL at 3-200 keV. Results. 0716+714 was in an exceptionally high state and different (slower) phase of short-term variability, when compared to the past, most likely due to a pronounced outburst shortly before the campaign. The flux density variability in the cm- to mm-bands is dominated by a ~4 day time scale amplitude increase of up to ~35%, systematically more pronounced towards shorter wavelengths. The cross-correlation analysis reveals systematic time-lags with the higher frequencies varying earlier, similar to canonical variability on longer time-scales. The increase of the variability amplitudes with frequency contradicts expectations from standard interstellar scintillation (ISS) and suggests a source-intrinsic origin for the observed inter-day variability. We find an inverted synchrotron spectrum peaking near 90 GHz, with the peak flux increasing during the first 4 days. The lower limits to TBderived from the inter-day variations exceed the 1012 K IC-limit by up to 3-4 orders of magnitude. Assuming relativistic boosting, our different estimates of yield robust and self-consistent lower limits of ∂ ≥ 5-33 - in good agreement with ∂VLBIobtained from VLBI studies and the IC-Doppler factors ∂IC > 14-16 obtained from the INTEGRAL data. Conclusions. The non-detection of S5 0716+714 with INTEGRAL in this campaign excludes an excessively high X-ray flux associated with a simultaneous IC catastrophe. Since a strong contribution from ISS can be excluded, we conclude that relativistic Doppler boosting naturally explains the apparent violation of the theoretical limits. All derived Doppler factors are internally consistent, agree with the results from different observations and can be explained within the framework of standard synchrotron-self-Compton (SSC) jet models of AGN. © 2008 ESO.
• Halfen, D. T., & Ziurys, L. M. (2008). A confusion-limited spectral-line survey of Sgr B2(N) at 1, 2, and 3mm: Establishing the organic inventory in molecular clouds. Proceedings of the International Astronomical Union, 4(S251), 27-28.
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  Abstract: We present preliminary results of an spectral-line survey at 1, 2, and 3 mm of the galactic center cloud Sgr B2(N). With the current data, several simple prebiotic molecules have been conclusively identified, while several more complex molecules have not. When complete, this survey will provide an accurate database of the gas-phase organic inventory in Sgr B2(N). © 2008 International Astronomical Union.
• Halfen, D. T., & Ziurys, L. M. (2008). The submillimeter spectrum of MnH and MnD (X⁷Σ ⁺). Astrophysical Journal, 672(1 PART 2), L77-L80.
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  Abstract: The submillimeter-wave spectrum of the MnH and MnD radicals in their 7Σ+ ground states has been measured in the laboratory using direct absorption techniques. These species were created in the gas phase by the reaction of manganese vapor, produced in a Broida-type oven, with either H2 or D2 gas in the presence of a DC discharge. The N = 0 → 1 transition of MnH near 339 GHz was recorded, which consisted of multiple hyperfine components arising from both the manganese and hydrogen nuclear spins. The N = 2 → 3 transition of MnD near 517 GHz was measured as well, but in this case only the manganese hyperfine interactions were resolved. Both data sets were analyzed with a Hund's case b Hamiltonian, and rotational, fine structure, magnetic hyperfine, and electric quadrupole constants have been determined for the two manganese species. An examination of the magnetic hyperfine constants shows that MnH is primarily an ionic species, but has more covalent character than MnF. MnH is a good candidate species for astronomical searches with Herschel, particularly toward material associated with luminous blue variable stars. © 2008. The American Astronomical Society, All rights reserved.
• Halfen, D. T., Clouthier, D. J., & Ziurys, L. M. (2008). Detection of the CCP radical (X ²π_r) in IRC +10216: A new interstellar phosphorus-containing spectes. Astrophysical Journal, 677(2 PART 2), L101-L104.
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  Abstract: The CCP radical (X 2 πr) has been detected in the circumstellar gas of IRC +10216, the fifth phosphorus-bearing molecule identified in interstellar space. This identification was made on the basis of new laboratory millimeter/submillimeter direct absorption measurements, conducted in the range 120-413 GHz. Four rotational transitions of this species were observed using the Arizona Radio Observatory (ARO) 12 m telescope on Kitt Peak at 2 and 3 mm in wavelength. Each transition consists of lambda-doublets, which are well-separated in frequency in IRC +10216; five of these eight possible lines of CCP were clearly detected, while the remaining three were contaminated by stronger emission from other species. The column density derived for CCP was Ntot = 1.2 × 1012 cm-2 and Trot = 21 K. Modeling of the line profiles suggests that CCP arises from an extended shell with a maximum radius of ∼40". The abundance of this radical, relative to H2, is f ∼ 1 × 10-9 - roughly comparable to that of PN and CP in this source. CCP may be produced from radical-radical reactions of CP, or ion-molecule chemistry involving P + and HCCH. The identification of CCP is additional evidence that phosphorus chemistrv is active in carbon-rich circumstellar gas. © 2008. The American Astronomical Society. All right reserved.
• Halfen, D. T., Ziurys, L. M., Pearson, J. C., & Drouin, B. J. (2008). Direct measurements of the fundamental rotational transitions of CD and¹³CH (X ²Π_r). Astrophysical Journal, 687(1), 731-736.
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  Abstract: The lowest energy rotational transitions of CD and 13CH in their 2Πr ground electronic states have been directly measured using submillimeter direct absorption spectroscopy. These two radicals were produced in an electrical discharge of either CD4 (or CH 4 and D2) or 13CH4. The J = 3/2 ← 1/2, N = 1 ← 1 transition at 439 GHz and the J = 3/2 ← 3/2 and 5/2 ← 3/2 fine structure lines of the N = 2 ← 1 rotational transition near 885 GHz and 916 GHz were recorded for CD (Hund's case b notation), each of which consist of lambda doublets. In addition, hyperfine splittings due to the deuterium nuclear spin of I = 1 were measured in several doublets, although some hyperfine components were blended together at higher frequency. For 13CH, the lambda doublets of the fundamental N = 1 ← 1 line near 532-536 GHz were recorded; in this case, hyperfine interactions arising from both 13C and H nuclei were resolved. These data were fit with a case b effective Hamiltonian, and spectroscopic parameters were derived. In particular, the deuterium hyperfine constants for CD were improved by about an order of magnitude, while for 13CH the hydrogen Fermi contact and dipolar terms were established for the first time. These measurements will enable definitive searches for CD and 13CH in interstellar gas, in particular with the upcoming Herschel Space Observatory. © 2008. The American Astronomical Society. All rights reserved.
• Milam, S. N., Halfen, D. T., Tenenbaum, E. D., Apponi, A. J., Woolf, N. J., & Ziurys, L. M. (2008). Constraining phosphorus chemistry in carbon- and oxygen-rich circumstellar envelopes: Observations of PN, HCP, and CP. Astrophysical Journal, 684(1), 618-625.
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  Abstract: Millimeter-wave observations of PN, CP, and HCP have been carried out toward circumstellar envelopes of evolved stars using the Arizona Radio Observatory (ARO). HCP and PN have been identified in the carbon-rich source CRL 2688 via observations at 1 mm using the Submillimeter Telescope (SMT) and 2-3 mm with the Kitt Peak 12 m. An identical set of measurements were carried out toward IRC +10216, as well as observations of CP at 1 mm. PN was also observed toward VY Canis Majoris (VY CMa), an oxygen-rich supergiant star. The PN and HCP line profiles in CRL 2688 and IRC +10216 are roughly flat topped, indicating unresolved, optically thin emission; CP, in contrast, has a distinct "U" shape in IRC +10216. Modeling of the line profiles suggests abundances, relative to H2, of f(PN) ∼ (3-5) × 10 _9and f(HCP) ∼ 2 × 10-7 in CRL 2688, about an order of magnitude higher than in IRC +10216. In VY CMa, f(PN) is ∼4 × 10-8. The data in CRL 2688 and IRC +10216 are consistent with LTE formation of HCP and PN in the inner envelope, as predicted by theoretical calculations, with CP a photodissociation product at larger radii. The observed abundance of PN in VY CMa is a factor of 100 higher than LTE predictions. In IRC +10216, the chemistry of HCP/CP mimics that of HCN/CN and suggests an N 2 abundance of f ∼ 1 × 10-7. The chemistry of phosphorus appears active in both carbon- and oxygen-rich envelopes of evolved stars. © 2008. The American Astronomical Society. All rights reserved.
• Remuan, A. J., Milam, S. N., Womack, M., Apponi, A. J., Ziurys, L. M., Wyckoff, S., A'hearn, M., Pater, I. D., Forster, J. R., Friedel, D. N., Palmer, P., Snyder, L. E., Veal, J. M., Woodney, L. M., & Wright, M. C. (2008). The distribution, excitation, and formation of cometary molecules: Methanol, methyl cyanide, and ethylene glycol. Astrophysical Journal, 689(1), 613-621.
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  Abstract: We present an interferometric and single-dish study of small organic species toward Comets C/1995 01 (Hale-Bopp) and C/2002 T7 (LINEAR) using the BIMA interferometer at 3 mm and the ARO 12 m telescope at 2 mm. For Comet Hale-Bopp, both the single-dish and interferometer observations of CH3OH indicate an excitation temperature of 105 ± 5K and an average production rate ratio Q2(CH3OH)/Q(H2O) ̃ 1.3% at ̃1 AU. In addition, the aperture synthesis observations of CH3OH suggest a distribution well described by a spherical outflow and no evidence of significant extended emission. Single-dish observations of CH3CN in Comet Hale-Bopp indicate an excitation temperature of 200 ± 10 K and a production rate ratio of Q(CH3CN)/Q(H2O) ̃ 0.017% at ̃1 AU. The non detection of a previously claimed transition of cometary (CH2OH)2 toward Comet Hale-Bopp with the 12 m telescope indicates a compact distribution of emission, D < 9" (
• Sandqvist, A., Larsson, B., Hjalmarson, Å., Bergman, P., Bernath, P., Frisk, U., Olberg, M., Pagani, L., & Ziurys, L. M. (2008). Odin observations of the Galactic centre in the 118-GHz band: Upper limit to the O₂ abundance. Astronomy and Astrophysics, 482(3), 849-853.
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  Abstract: Aims. The Odin satellite has been used to search for the 118.75-GHz line of molecular oxygen (O) in the Galactic centre.Methods. Odin observations were performed towards the Sgr circumnuclear disk (CND), and the Sgr A +20 km s and +50 km s molecular clouds using the position-switching mode. Supplementary ground-based observations were carried out in the 2-mm band using the ARO Kitt Peak 12-m telescope to examine suspected SiC features.Results. A strong emission line was found at 118.27 GHz, attributable to the HCN line. Upper limits are presented for the 118.75-GHz O ground transition line and for the 118.11-GHz , ground state SiC line at the Galactic centre. Upper limits are also presented for the 487-GHz O line in the Sgr A +50 km s cloud and for the 157-GHz, , SiC line in the Sgr A +20 and +50 km s clouds, as well as the CND. The CHOH line complex at 157.2-157.3 GHz has been detected in the +20 and +50 kms clouds but not towards Sgr /CND.Conclusions. A upper limit for the fractional abundance ratio of [ O] /[ H] is found to be (O) towards the Sgr A molecular belt region. © 2008 ESO.
• Tenenbaum, E. D., & Ziurys, L. M. (2008). A search for phosphine in circumstellar envelopes: PH₃ in IRC +10216 and CRL 2688?. Astrophysical Journal, 680(2 PART 2), L121-L124.
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  Abstract: We present the results of a search for the JK = 1 o→0o transition of PH3 (phosphine) at 267 GHz toward several circumstellar envelopes using the Arizona Radio Observatory 10 m Submillimeter Telescope (SMT). In the carbon-rich shells of IRC +10216 and CRL 2688, we have detected emission lines exactly at the PH3 frequency. Toward the oxygen-rich supergiant VY Canis Majoris, only an upper limit was obtained, while in the evolved carbon-rich proto-planetary nebula CRL 618, the transition is contaminated by vibrational excited HC3N (V7 = 4). The line shape in IRC +10216 appears to consist of two distinct components: a flat-topped profile with a width of ∼28 km s -1, as is typical for this source, and a narrower feature approximately 4 km s″1 wide. The narrow component likely arises from the inner envelope (r < 8R*) where the gas has not reached the terminal expansion velocity, or it is nonthermal emission. Based on the broader component, the abundance of PH3 with respect to H2 is estimated to be 5 x 10-8 in a region with a radius of r< 150R*. If the narrower component is thermal, it implies a phosphine abundance of ~5 x 10-7 close to the stellar photosphere (r< 8R*). In CRL 2688, the PH3 abundance is less constrained, with plausible values ranging from 3 x 10 -8 to 4 x 10-7, assuming a spherical distribution. Phosphine appears to be present in large concentrations in the inner envelope of C-rich AGB stars, and thus may function as a parent molecule for other phosphorus species. © 2008, The American Astronomical Society, AU rights reserved.
• Tenenbaum, E. D., Milam, S. N., Apponi, A. J., Woolf, N. J., Ziurys, L. M., & Schöier, F. L. (2008). The 1 mm spectrum of VY Canis Majoris: Chemistry in an O-rich envelope. Proceedings of the International Astronomical Union, 4(S251), 171-172.
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  Abstract: We present preliminary results of an unbiased spectral survey at 1 mm of the oxygen-rich supergiant, VY CMa. A number of exotic molecules have been detected, including NaCl and PO, and a relatively rich organic chemistry is observed. Results of the survey will be compared with carbon-rich stars. © 2008 International Astronomical Union.
• Ziurys, L. M. (2008). Organic chemistry in circumstellar envelopes: Setting the stage for prebiotic synthesis. Proceedings of the International Astronomical Union, 4(S251), 147-156.
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  Abstract: One of the few carbon-rich environments found in interstellar space is the ejecta of asymptotic giant branch (AGB) stars. Such material, which forms a circumstellar envelope, becomes enriched in carbon due to dredge-up phenomena associated with nucleosynthesis. A unique organic synthesis flourishes in the gas phase in these envelopes, and radio and millimeter observations have identified a wide range of C-bearing compounds, including long acetylenic chains such as HC5N, HC7N, C4H, C6H, C8H, C6H, C8H, and C3O. Oxygen-rich envelopes also have a non-negligible carbon chemistry, fostering species such as HCN and HCO+. Phosphorus chemistry appears to be active as well in circumstellar shells, as evidenced by the recent detections of HCP, CCP, and PO. Radio observations also indicate that some fraction of the circumstellar molecular material survives into the planetary nebula stage, and then becomes incorporated into diffuse, and eventually, dense clouds. The complex organic molecules found in dense clouds such as Sgr B2(N) may be the products of seed material that can be traced back to the carbon-enriched circumstellar gas. © 2008 International Astronomical Union.
• Flory, M. A., Field, R. W., & Ziurys, L. M. (2007). The pure rotational spectrum of CrCN (X ⁶∑⁺): An unexpected geometry and unusual spin interactions. Molecular Physics, 105(5-7), 585-597.
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  Abstract: The pure rotational spectrum of CrCN (X 6+) has been recorded in the frequency range 250-520 GHz using direct-absorption techniques. This is the first spectroscopic investigation of the CrCN radical. This species was synthesized by reacting Cr vapour with (CN)2. Spectra were obtained for the main isotopic species, the 53Cr and 13C isotopologues, and the heavy atom stretch and several quanta of the bending vibration. The molecule was found to have a linear cyanide geometry and a 6+ ground state. Rotational, fine structure, and l-type doubling constants have been determined. The spin-spin parametre was found to be small-a likely result of competing second-order spin-orbit contributions from excited 4-, 4, and 6 states. However, increased significantly in the bending mode, which may be caused by a reduction of the 6+-4 interaction strength due to spin-orbit vibronic coupling. In contrast, the value of , arising from interactions with a nearby 6state, was independent of v2. The CrCN bond lengths were determined to be rCr-C = 2.019 and rC-N = 1.148 . Delocalization of the 3d electrons into the CN 2* orbital, which is polarized towards the carbon atom, may account for the CrCN structure.
• Halfen, D. T., & Ziurys, L. M. (2007). Laboratory detection of FeCO⁺ (X⁴Σ^-) by millimeter/submillimeter velocity modulation spectroscopy. Astrophysical Journal, 657(1 II), L61-L64.
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  Abstract: The millimeter/submillimeter spectrum of the molecular ion FeCO+ (X4Σ-) has been recorded using velocity modulation spectroscopy. The molecular ion was created in an AC discharge of Fe(CO) 5 and argon. Twentyseven rotational transitions, each consisting of four fine-structure components, were measured in the range 198-418 GHz. The data were fit with a case b Hamiltonian, and rotational, spin-rotation, and spin-spin constants were determined. Because of the presence of higher order spin-orbit interactions, probably caused in part by a nearby 4II excited state, numerous centrifugal distortion terms were needed for the spectral analysis. The value of γs, the third-order spin-rotation constant, was also remarkably large at -72.4 MHz. Rest frequencies for FeCO+ are now available for interstellar and circumstellar searches. This species may be present in molecular clouds, where CO is abundant and gas-phase iron should be in the form of Fe+. Molecular ions such as FeCO+ could be the hidden carriers of metallic elements in such clouds. © 2007. The American Astronomical Society. All rights reserved.
• Harrison, J. J., Brown, J. M., Flory, M. A., Sheridan, P. M., McLamarrah, S. K., & Ziurys, L. M. (2007). The rotational spectrum of CoF in all three spin-orbit components of the X φi3 state. Journal of Chemical Physics, 127(19).
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  Abstract: The pure rotational spectrum of cobalt monofluoride in its X i3 electronic state has been measured in the frequency range of 256-651 GHz using direct absorption techniques. CoF was created by reacting cobalt vapor with F2 in helium at low pressure (25-30 mTorr). All three spin components were identified in the spectrum of this species, two of which exhibited lambda doubling. Each spin component showed hyperfine splittings from both nuclei: an octet pattern arising from the Co59 spin of I=72, which is further split into doublets due to the F19 nucleus (I=12). The data were fitted close to experimental precision using an effective Hamiltonian expressed in Hund's case (a) form, and rotational, fine structure, hyperfine, and lambda-doubling parameters were determined. There is evidence that the rotational levels of the highest spin component 23 are perturbed. The r0 bond length of CoF was estimated from the rotational constant to be 1.738 014 (1) Å. This value is in good agreement with previous studies but much more accurate. The matrix elements necessary for the complete treatment of doubling in a state have been derived and are presented for the first time. © 2007 American Institute of Physics.
• Lyons, C. M., Lichtenberger, A. W., Kerr, A. R., Lauria, E. F., & Ziurys, L. M. (2007). Fabrication of a Nb-based 180-degree if hybrid for balanced SIS mixers. IEEE Transactions on Applied Superconductivity, 17(2), 194-197.
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  Abstract: 180-degree IF hybrids are potentially useful for balanced superconductor-insulator-superconductor (SIS) mixers. We have developed a compact Nb-based 180-degree hybrid for 4-12 GHz which addresses concerns of element size, ohmic loss, and IF bandwidth. The fabrication scheme developed for these elements will be discussed, including the use of a thin overlayer Au process for via contacts, RF diode sputtered SiOx in lieu of sublimated SiO films in order to improve the wafer yield, and diagnostic Nb capacitors to evaluate these SiOx films. Experimental results will be presented and compared with simulations of these lumped element transmission line "rat-race" hybrids. It should be noted that the hybrids can be used in cryogenic balanced mixers for any RF band. © 2007 IEEE.
• Milam, S. N., Apponi, A. J., Woolf, N. J., & Ziurys, L. M. (2007). Oxygen-rich mass loss with a pinch of salt: Nacl in the circumstellar gas of ik tauri and vy canis majoris. Astrophysical Journal, 668(2 PART 2), L131-L134.
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  Abstract: The NaCl molecule has been observed in the circumstellar envelopes of VY Canis Majoris (VY CMa) and IK Tauri (IK Tau) - the first identifications of a metal refractory in oxygen-rich shells of evolved stars. Five rotational transitions of NaCl at 1 and 2 mm were detected toward VY CMa and three 1 mm lines were observed toward IK Tau, using the telescopes of the Arizona Radio Observatory. In both objects, the line widths of the NaCl profiles were extremely narrow relative to those of other molecules, indicating that sodium chloride has not reached the terminal outflow velocity in either star, likely a result of early condensation onto grains. Modeling the observed spectra suggests abundances, relative to H2, of 5 × 10-9 in VY CMa and ∞ × 10-9 in IK Tau, with source sizes of 0.5" and 0.3", respectively. The extent of these sources is consistent with the size of the dust acceleration zones in both stars. NaCl therefore appears to be at least as abundant in O-rich shells as compared to C-rich envelopes, where ∞ ∼ (0.2-2) × 10-9, although it appears to condense out earlier in the O-rich case. Chemical equilibrium calculations indicate that NaCl is the major carrier of sodium at T ∼ 1100 K for oxygen-rich stars, with predicted fractional abundances in good agreement with the observations. These measurements suggest that crystalline salt may be an important condensate for sodium in both C- and O-rich circumstellar shells. © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Tenenbaum, E. D., Flory, M. A., Pulliam, R. L., & Ziurys, L. M. (2007). The pure rotational spectrum of ZnCl (X²Σ⁺): Variations in zinc halide bonding. Journal of Molecular Spectroscopy, 244(2), 153-159.
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  Abstract: The radical ZnCl (X2Σ+) has been studied using millimeter-wave direct-absorption techniques. Pure rotational spectra of 67Zn35Cl, 66Zn37Cl, 68Zn35Cl, 64Zn35Cl, 64Zn37Cl, and 66Zn35Cl were measured in the vibrational ground state and data were also recorded for the latter three in the v = 1 and v = 2 states. Every rotational transition was found to be split into a doublet due to spin-rotation interactions. For 67Zn35Cl, each doublet exhibited additional splittings arising from hyperfine coupling of the 67Zn (I = 5/2) nucleus. Rotational, fine structure, and hyperfine constants have been determined from these data, and equilibrium parameters calculated. The equilibrium bond length of 64Zn35Cl is found to be 2.13003305(24) Å, in good agreement with recent theoretical predictions. Interpretation of hyperfine constants indicates that the 12σ orbital is ∼70% Zn(4s) in character, suggesting that the zinc chloride bond is relatively ionic.
• Tenenbaum, E. D., Woolf, N. J., & Ziurys, L. M. (2007). Identification of phosphorus monoxide (x²ii_r) in vy canis majoris: Detection of the first pio bond in space. Astrophysical Journal, 666(1 PART 2), L29-L32.
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  Abstract: A new interstellar molecule, PO (X 2IIr), has been detected toward the envelope of the oxygen-rich supergiant star VY Canis Majoris (VY CMa) using the Submillimeter Telescope of the Arizona Radio Observatory. The J p 5.5 → 4.5 and J = 6.5 → 5.5 rotational transitions of PO at 240 and 284 GHz were observed, each of which consisted of well-defined lambda-doublets. The line profiles are roughly parabolic in shape, analogous to PN, and suggest that this species arises from the spherical wind in VY CMa, as opposed to the collimated blue- and redshifted outflows. Comparison of line intensities indicates that PO arises from a confined source roughly 1″ in extent, with a column density of Ntot ≈ 2.8 # 1015 cm-2, which corresponds to a fractional abundance of/∼ 9 × 10-8, relative to H2. Consequently, PO and PN have similar concentrations in VY CMa, a result not predicted by either LTE or kinetic models of circumstellar chemistry. These phosphorus compounds may arise from shock-induced reactions in this active envelope. Phosphorus monoxide is the first interstellar molecule detected that contains a P - O bond, a moiety essential in biochemical compounds. It is also the first new species to be identified in an oxygen-rich, as opposed to a carbon-rich, circumstellar envelope. © 2007. The American Astronomical Society. All rights reserved. Printed in U.S.A.
• Ziurys, L. M., Milam, S. N., Apponi, A. J., & Woolf, N. J. (2007). Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris. Nature, 447(7148), 1094-1097.
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  PMID: 17597755;Abstract: The interstellar medium is enriched primarily by matter ejected from old, evolved stars. The outflows from these stars create spherical envelopes, which foster gas-phase chemistry. The chemical complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of molecules than their oxygen-rich analogues. Here we report observations of molecules in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chemical compounds have been identified, including NaCl, PN, HNC and HCO+. From the spectral line profiles, the molecules can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulphur-bearing molecules (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO+ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chemically diverse as their carbon counterparts. ©2007 Nature Publishing Group.
• Apponi, A. J., Halfen, D. T., Ziurys, L. M., Hollis, J. M., Remijan, A. J., & Lovas, F. J. (2006). Investigating the limits of chemical complexity in sagittarius B2(N): A rigorous attempt to confirm 1,3-dihydroxyacetone. Astrophysical Journal Letters, 643(1 II), L29-L32.
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  Abstract: A search for confirming transitions of 1,3-dihydroxyacetone, (CH 2OH)2CO (hereafter DHA), has been made toward Sgr B2(N) using the Arizona Radio Observatory Submillimeter Telescope (SMT) and 12 m telescope at millimeter wavelengths. In addition, data for this species have been obtained at the Green Bank Telescope. In all, 63 new transitions of DHA were sought; no plausible emission was detected at 97% of these frequencies. Typical peak-to-peak limits of 10-30 mK were achieved, indicating that DHA is not present in Sgr B2(N) at the level reported by Widicus Weaver & Blake in 2005, by at least a factor of 300. The upper limit to the DHA column density is Ntot < 5 × 1013 cm-2, suggesting that this species, a three-carbon keto sugar, is less abundant than the two-carbon aldehyde sugar, glycolaldehyde (CH2OHCHO), by a factor of at least 4. If sugars of higher complexity are formed in interstellar clouds, their synthesis may proceed one carbon atom at a time, possibly through aldehyde intermediates. © 2006. The American Astronomical Society. All rights reserved.
• Apponi, A. J., Hoy, J. J., Halfen, D. T., Ziurys, L. M., & Brewster, M. A. (2006). Hydroxyacetone (CH₃COCH₂OH): A combined microwave and millimeter-wave laboratory study and associated astronomical search. Astrophysical Journal, 652(2 I), 1787-1795.
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  Abstract: A combined laboratory and astronomical investigation has been conducted on the methyl sugar hydroxyacetone (CH3COCH2OH). Rotational transitions of this species in the ground torsional state (vt = 0) were recorded using both millimeter-wave direct absorption techniques and Fourier transform microwave spectroscopy. A total of 1145 lines of CH 3COCH2OH were analyzed in the frequency range 4 to 180 GHz, including transitions arising from both A- and E-symmetry species. A modified rho-axis method Hamiltonian was needed for the analysis because of the presence of perturbations resulting from the torsional motion of the methyl group in this molecule. Assignment of the E-species was particularly problematic as a consequence of significant mixing between the ground and torsionally excited levels. The complete data set was fitted using 21 spectroscopic parameters and had a global rms of 90 kHz; the barrier to internal rotation was established to be 65.3560(22) cm-1. An astronomical search was subsequently conducted for hydroxyacetone at 2 and 3 mm using the 12 m telescope of the Arizona Radio Observatory. Twenty-eight favorable transitions arising from both A- and E-species, each consisting of collapsed quartets, were searched for toward Sgr B2(N). Although credible features were detected at several frequencies of hydroxyacetone, there were a sufficient number of missing lines to rule out an interstellar detection. An upper limit to the column density of Ntot < 5 × 1012 cm-2 was derived for CH3COCH2OH in Sgr B2(N), indicating that this species is an order of magnitude less abundant than glycolaldehyde (CH2OHCHO). © 2006. The American Astronomical Society. All rights reserved.
• Flory, M. A., McLamarrah, S. K., & Ziurys, L. M. (2006). Completing the 3d metal fluoride series: The pure rotational spectrum of ZnF (X²∑⁺). Journal of Chemical Physics, 125(19).
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  Abstract: The pure rotational spectrum of the ZnF radical has been recorded in the range of 176-527 GHz using millimeter/submillimeter direct absorption techniques. This study is the first gas-phase spectroscopic investigation of this species. Between 5 and 11 transitions were measured for each of five isotopologues of this radical (Zn64 F, Zn66 F, Zn67 F, Zn68 F, and Zn70 F) in the ground and several excited vibrational (v=1, 2, and 3) states. Each transition consists of spin-rotation doublets with a splitting of ∼150 MHz, indicating that the electronic ground state of ZnF is +2, as predicted by theory. Fluorine hyperfine splitting was observed in three isotopologues (Zn64 F, Zn66 F, and Zn67 F), and hyperfine structure from the zinc-67 nucleus (I=52) was additionally resolved in Zn67 F. Rotational, fine structure, and F19 and Zn67 hyperfine constants were determined for ZnF, as well as equilibrium parameters. The bond length of the main isotopologue Zn64 F was calculated to be re =1.7677 Å. Evaluation of the hyperfine constants indicates that the orbital containing the unpaired electron is ∼80% 4s (Zn) in character with ∼10% contributions from each of the 2p (F) and 4p (Zn) orbitals. These results imply that ZnF is somewhat less ionic than CaF, as suggested by theory. © 2006 American Institute of Physics.
• Halfen, D. T., & Ziurys, L. M. (2006). Velocity modulation spectroscopy of molecular ions II: The millimeter/submillimeter-wave spectrum of TiF⁺ (X³Φ_r). Journal of Molecular Spectroscopy, 240(1), 58-63.
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  Abstract: The pure rotational spectrum of the molecular ion TiF+ in its 3Φr ground state has been measured in the range 327-542 GHz using millimeter-wave direct absorption techniques combined with velocity modulation spectroscopy. TiF+ was made in an AC discharge from a mixture of TiCl4, F2 in He, and argon. Ten transitions of this ion were recorded. In every transition, fluorine hyperfine interactions, as well as the fine structure splittings, were resolved. The fine structure pattern was found to be regular with almost equal spacing in frequency between the three spin components, in contrast to TiCl+, which is perturbed in the ground state. The data were fit with a case (a) Hamiltonian and rotational, fine structure, and hyperfine constants were determined. The bond length established for TiF+, r0 = 1.7775 Å, was found to be shorter than that of TiF, r0 = 1.8342 Å-also established from mm-wave data. The hyperfine parameters determined are consistent with a δ1π1 electron configuration with the electrons primarily located on the titanium nucleus. The nuclear spin-orbit constant a indicates that the unpaired electrons are closer to the fluorine nucleus in TiF+ relative to TiF, as expected with the decrease in bond length for the ion. The shorter bond distance is thought to arise from increased charge on the titanium nucleus as a result of a Ti2+F- configuration. A similar decrease in bond length was found for TiCl+ relative to TiCl. © 2006 Elsevier Inc. All rights reserved.
• Harrison, J. J., Brown, J. M., Halfen, D. T., & Ziurys, L. M. (2006). Improved frequencies of rotational transitions of⁵²CrH in the ⁶Σ⁺ ground state. Astrophysical Journal Letters, 637(2 I), 1143-1147.
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  Abstract: Previous mid-infrared, far-infrared, and new submillimeter data relating solely to 52CrH in its X6Σ+ state have been reanalyzed by a least-squares fit using a Hund's case (b) Hamiltonian to determine the best obtainable set of parameters for the molecule. In particular, the fine structure and hyperfine constants have been improved. From these parameters, transition frequencies are determined that are more reliable than those published previously; the latter show systematic errors of up to 15 MHz. Such frequencies will facilitate the identification of CrH in the interstellar medium. © 2006. The American Astronomical Society. All rights reserved.
• Janczyk, A., & Ziurys, L. M. (2006). Laboratory detection and pure rotational spectrum of AlSH (X̃¹A′). Astrophysical Journal Letters, 639(2 II), L107-L110.
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  Abstract: The pure rotational spectrum of AlSH (X̃ 1A′) has been recorded using millimeter and submillimeter direct absorption techniques. Measurements of its deuterium isotopomer have been recorded as well. This study is the first laboratory detection of this molecule, which was created by the reaction of aluminum vapor and H2S. Nine and seven rotational transitions of AlSH and AlSD were measured, respectively, each consisting of Ka = 0 through Ka = 6 asymmetry components. From these data, rotational constants have been established. Calculation of an r 0 structure indicates that AlSH is bent with an angle near 90°. These measurements will enable searches for AlSH to be carried out in circumstellar gas, where aluminum-bearing molecules, as well as H2S, are present. © 2006. The American Astronomical Society. All rights reserved.
• Janczyk, A., & Ziurys, L. M. (2006). Sub-millimeter spectroscopy of BaS (X¹Σ⁺). Journal of Molecular Spectroscopy, 236(1), 11-15.
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  Abstract: The pure rotational spectrum of BaS (X1Σ+) has been recorded in the frequency range 355-396 GHz using direct absorption methods. Data were recorded for six isotopomers: 138Ba32S, 137Ba32S, 136B32S, 135Ba32S, 134Ba32S, and 138Ba34S, in vibrational states ranging from v = 0 to v = 6. This work is an extension of past microwave and millimeter studies. Revised spectroscopic constants have been established for the six species. The dissociation energy for 138Ba32S is estimated to be DEhc∼ 42 392 cm-1. © 2005 Elsevier Inc. All rights reserved.
• Kerr, A. R., Lichtenberger, A. W., Lyons, C. M., Lauria, E. F., Ziurys, L. M., & Lambeth, M. R. (2006). A superconducting 180° if hybrid for balanced sis mixers. 17th International Symposium on Space Terahertz Technology 2006, ISSTT 2006, 7-10.
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  Abstract: A compact 180° hybrid has been developed for use in balanced SIS mixers. The lumped-element circuit uses superconducting Nb conductors on a 1.4 mm x 0.5 mm quartz substrate and operates over 4-12 GHz. Index Terms-Superconducting microwave devices, microwave integrated circuits, hybrid junctions, lumpedelement microwave circuits, superconductor-insulatorsuperconductor mixers.
• Milam, S. N., Remijan, A. J., Womack, M., Abrell, L., Ziurys, L. M., Wyckoff, S., Apponi, A. J., Friedel, D. N., Snyder, L. E., Veal, J. M., Palmer, P., Woodney, L. M., A'Hearn, M. F., Forster, J. R., Wright, M. C., Pater, I. D., Choi, S., & Gesmundo, M. (2006). Formaldehyde in comets C/1995 O1 (Hale-Bopp), C/2002 T7 (LINEAR), and C/2001 Q4 (NEAT): Investigating the cometary origin of H₂CO. Astrophysical Journal Letters, 649(2 I), 1169-1177.
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  Abstract: Observations of formaldehyde (H2CO) have been conducted toward comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H2CO at 3 mm were made using the Berkeley-Illinois-Maryland Association (BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H2CO is ∼3.7 × 1028 s-1 at ∼1 AU in comet Hale-Bopp, using a simple Monte Carlo model, if a nuclear origin for the molecule is assumed. However, maps of H2CO in Hale-Bopp, in comparison with CO, show an extended distribution (rs ∼ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H2CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H2CO increases to Q ∼ 1.4 × 1029 s-1 assuming such an extended grain source. This value implies a Q/Q(H2O) ∼ 1.4%, which is similar to the production rate ratio of Q/Q(H2O) ∼ 4% derived from in situ measurements of H2CO in comet Halley. Production rates for H 2CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 (NEAT) are 1.4 × 1027 and 5.6 × 1026 s-1, respectively, modeled using the extended grain source. The spectra of H 2CO measured toward comet C/2002 T7 (LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation.
• Milam, S. N., Ziurys, L. M., Woolf, N. J., & Wyckoff, S. (2006). Carbon isotope ratios in circumstellar envelopes: Constraints for nucleosynthesis and galactic chemical evolution. AIP Conference Proceedings, 855, 165-169.
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  Abstract: Observations of the 1→0 transition of the 12C and 13C isotopomers of CO and CN at 1.2 and 3 mm have been conducted towards various circumstellar envelopes, using the Kitt Peak 12m antenna and the Submillimeter Telescope (SMT) of the Arizona Radio Observatory (ARO). These observations have been used to establish 12C/13C ratios in these objects. CN is particularly useful in this regard because its spectra exhibit hyperfine structure from which accurate opacities can be evaluated. Observations include a variety of hydrogen-deficient stars, supergiants, Li-rich, M, S, and C stars. Measurements towards Asymptotic Giant Branch (AGB) stars (e.g. IRC+10216, CRL618, CRL2688, and IRC+40540), suggest preliminary 12C/13C isotope ratios in the range of 20-76, while in supergiants, 12C/13C ∼ 3-10. Theory predicts that carbon-12 is primarily formed in massive stars that evolve into Type II supernovae, while carbon-13 is produced from the CNO cycle occurring in intermediate mass AGB stars. Ratios determined for these objects with multiple molecular species help constrain nucleosynthesis models and provide insight into the 12C/13C Galactic gradient measured in molecular clouds, as well as local variations of this ratio found in the interstellar medium. © 2006 American Institute of Physics.
• Tenenbaum, E. D., Apponi, A. J., Ziurys, L. M., Agúndez, M., Cernicharo, J., Pardo, J. R., & Guélin, M. (2006). Detection of C₃O in IRC +10216: Oxygen-carbon chain chemistry in the outer envelope. Astrophysical Journal Letters, 649(1 II), L17-L20.
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  Abstract: The oxygen-bearing species C3O has been identified in the circumstellar envelope of the carbon star IRC +10216. The J = 8 → 7, 9 → 8, 10 → 9, 14 → 13, and 15 → 14 transitions were detected at 2 and 3 mm using the Arizona Radio Observatory's 12 m telescope. Measurements of the J = 9 → 8, 10 → 9, and 12 → 11 lines were simultaneously conducted at the IRAM 30 m telescope. The line profiles of C3O are roughly U-shaped, indicating an extended shell distribution for this molecule in IRC +10216. The total column density derived for C3O is 1.2 × 1012 cm-2, at least an order of magnitude higher than that predicted by current chemical models. However, a revised model that includes reactions of atomic oxygen with carbon-chain radicals, such as 1-C3H and C4, can reproduce the observed abundance. This model also predicts that C3O arises from a shell source with an outer radius near r ∼ 30″, consistent with the observations. These results suggest that gas phase neutral-neutral chemistry may be producing the oxygen-bearing molecules present in the outer envelope of IRC +10216. © 2006. The American Astronomical Society. All rights reserved.
• Ziurys, L. M. (2006). Millimeter-wave spectroscopy of metal-bearing molecules in the ISM. AIP Conference Proceedings, 855, 231-242.
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  Abstract: Over the past thirty years of millimeter astronomy, a great deal has been learned about interstellar molecules and their chemistry. Despite this progress, there are still areas of molecular astrophysics where challenges remain. One of these areas concerns the chemistry and distribution of molecules containing metals. Identifying the carriers of these elements in the interstellar medium, including circumstellar gas, is crucial for the evaluation of dust grain composition, ionization balance, mass loss from evolved stars, and elemental depletions. Over the past decade, the Ziurys group has been actively involved in both the laboratory measurement of the millimeter/sub-millimeter spectra of metal-containing molecules and in radio astronomical searches for these species in the ISM. A wide variety of small, metal-bearing species have been studied in our laboratory in the gas-phase using direct absorption techniques. These compounds include diatomic hydrides, halides, carbides, nitrides, oxides, and sulfides, and the polyatomic amides, hydroxides, acetylides, and cyanides. Some of the species recently studied are CrH (X6Σ+), CaC (X3Σ-), AlSH (X1A′), AlNC (X 1Σ+), and CoCN (X 3i). We have begun to study metal-bearing molecular ions as well (TiCl+: X 3r; VCl+: X4Σ-; FeCO+: X4Σ-; for example), using a new millimeter/sub-millimeter velocity modulation system. A new Fourier transform microwave spectrometer has also just been completed and will be used for laser-ablation investigations of such species. Radio astronomical searches have been made for almost all of these molecules, using the Arizona Radio Observatory's facilities and the IRAM 30 m telescope. Interestingly, besides the halides, only metal cyanide and isocyanide species have been detected in astronomical sources, and only in circumstellar envelopes of carbon-rich AGB stars. Among the molecules identified are AlNC, MgCN, and KCN. Metal-bearing species have been generally found in the envelope of the carbon star IRC+10216, but some are also present in other circumstellar shells of such objects as CRL2688 and CRL618. Nucleosynthesis occurs in AGB stars, and may produce metals such as sodium and magnesium. Therefore, the metal-bearing molecules detected in AGB envelopes may reflect enhancements in elemental abundances resulting from such nucleosynthesis, rather than cosmic abundances. Such elements would be mixed into the circumstellar shell in the third dredge-up, which also brings carbon to the stellar surface, creating a C-rich envelope. Additional metal-containing molecules need to be observed in AGB shells to verify this connection. These observations await new laboratory spectra. Metal cyanide/isocyanide compounds are the obvious choices for such laboratory work, in particular FeNC. This species has remained elusive, although the spectrum of CrCN has now been measured. © 2006 American Institute of Physics.
• Ziurys, L. M. (2006). The chemistry in circumstellar envelopes of evolved stars: Following the origin of the elements to the origin of life. Proceedings of the National Academy of Sciences of the United States of America, 103(33), 12274-12279.
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  PMID: 16894164;PMCID: PMC1567870;Abstract: Mass loss from evolved stars results in the formation of unusual chemical laboratories: circumstellar envelopes. Such envelopes are found around carbon- and oxygen-rich asymptotic giant branch stars and red supergiants. As the gaseous material of the envelope flows from the star, the resulting temperature and density gradients create a complex chemical environment involving hot, thermodynamically controlled synthesis, molecule "freeze-out," shock-initiated reactions, and photochemistry governed by radical mechanisms. In the circumstellar envelope of the carbon-rich star IRC+10216, >50 different chemical compounds have been identified, including such exotic species as C 8H, C3S, SiC3, and AINC. The chemistry here is dominated by molecules containing long carbon chains, silicon, and metals such as magnesium, sodium, and aluminum, which makes it quite distinct from that found in molecular clouds. The molecular composition of the oxygen-rich counterparts is not nearly as well explored, although recent studies of VY Canis Majoris have resulted in the identification of HCO+, SO2, and even NaCl in this object, suggesting chemical complexity here as well. As these envelopes evolve into planetary nebulae with a hot, exposed central star, synthesis of molecular ions becomes important, as indicated by studies of NGC 7027. Numerous species such as HCO+, HCN, and CCH are found in old planetary nebulae such as the Helix. This "survivor" molecular material may be linked to the variety of compounds found recently in diffuse clouds. Organic molecules in dense interstellar clouds may ultimately be traced back to carbon-rich fragments originally formed in circumstellar shells. © 2006 by The National Academy of Sciences of the USA.
• Flory, M. A., McLamarrah, S. K., & Ziurys, L. M. (2005). High-resolution spectroscopy of CoS (X ⁴ Δ _i): Examining 3d transition-metal sulfide bonds. Journal of Chemical Physics, 123(16).
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  Abstract: The pure rotational spectrum of CoS, the cobalt sulfide radical, has been measured using direct absorption techniques in the frequency range of 180-540 GHz. This study is the first spectroscopic investigation of any kind of this molecule. CoS was created by reacting cobalt vapor with H2 S. Four spin components were identified in the spectra of this species, one of which exhibited lambda doubling, identifying the ground state as Δi4. Transitions arising from the lowest spin component of the less abundant Co S34 isotopomer have also been detected, as well as from v=1 and v=2 of the main species. The spectra were readily identified because each spin component exhibited an octet pattern arising from the Co59 spin of I=72. The data were fit using Hund's case (a) Hamiltonian, and rotational, fine-structure, hyperfine, and lambda-doubling constants were determined. The hyperfine parameters support a δ3 π 2 electron configuration and are consistent with some orbital overlap between the metal and sulfur atoms. From the rotational constant, the bond length of CoS was calculated to be r0 =1.977 985 06 (10) Å. This bond length is significantly shorter than that of MnS or FeS, in contrast to the bond distances found in the oxide analogs which are all similar in value. These results indicate that the 3d metal sulfides differ somewhat from their oxide counterparts, probably due to the availability of sulfur p orbitals for bonding. © 2005 American Institute of Physics.
• Halfen, D. T., & Ziurys, L. M. (2005). Molecules in high spin states III: The millimeter/submillimeter-wave spectrum of the MnCl radical (X ⁷Σ ⁺). Journal of Chemical Physics, 122(5).
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  Abstract: The pure rotational spectrum of the MnCl radical (X 7Σ +) has been recorded in the range 141-535 GHz using millimeter-submillimeter direct absorption spectroscopy. This work is the first time the molecule has been studied with rotational resolution in its ground electronic state. MnCl was synthesized by the reaction of manganese vapor, produced in a Broida-type oven, with Cl 2. Transitions of both chlorine isotopomers were measured, as well as lines originating in several vibrationally excited states. The presence of several spin components and manganese hyperfine interactions resulted in quite complex spectra, consisting of multiple blended features. Because 42 rotational transitions were measured for Mn 35Cl over a wide range of frequencies with high signal-to-noise, a very accurate set of rotational, fine structure, and hyperfine constants could be determined with the aid of spectral simulations. Spectroscopic constants were also determined for Mn 37Cl and several vibrationally excited states. The values of the spin-rotation and spin-spin parameters were found to be relatively small (γ=11.2658 MHz and λ=1113.10 MHz for Mn 35Cl); in the case of λ, excited electronic states contributing to the second-order spin-orbit interaction may be canceling each other. The Fermi contact hyperfine term was found to be large in manganese chloride with b F(Mn 35Cl)=397.71MHz, a result of the manganese 4s character mixing into the 12σ orbital. This orbital is spσ hybridized, and contains some Mn 4pσ character, as well. Hence, it also contributes to the dipolar constant c, which is small and positive for this radical (c=32.35MHz for Mn 35Cl). The hyperfine parameters in MnCl are similar to those of MnH and MnF, suggesting that the bonding in these three molecules is comparable. © 2005 American Institute of Physics.
• Halfen, D. T., & Ziurys, L. M. (2005). Velocity modulation spectroscopy of molecular ions I: The pure rotational spectrum of TiCl⁺ (X³Φ_r). Journal of Molecular Spectroscopy, 234(1), 34-40.
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  Abstract: The pure rotational spectrum of the TiCl+ ion in its X 3Φr ground state has been measured in the frequency range 323-424 GHz, using a combination of direct absorption and velocity modulation techniques. The ion was created in an AC discharge of TiCl 4 and argon. Ten, eleven, and nine rotational transitions were recorded for the 48Ti35Cl+, 48Ti37Cl+, and 46Ti 35Cl+ isotopomers, respectively; fine structure splittings were resolved in every transition. The rotational fine structure pattern was irregular with the Ω = 4 component lying in between the Ω = 2 and 3 lines. This result is consistent with the presence of a nearby 3Δr state, which perturbs the Ω = 2 and 3 sub-levels, shifting their energies relative to the Ω = 4 component. The data for each isotopomer were analyzed in a global fit, and rotational and fine structure parameters were determined. The value of the spin-spin constant was comparable to that of the spin-orbit parameter, indicating a large second-order spin-orbit contribution to this interaction. The bond length established for TiCl+, r0 = 2.18879 (7) Å, is significantly shorter than that of TiCl, which has r0 = 2.26749 (4) Å. The shorter bond length likely results from a Ti2+Cl- structure in the ion relative to the neutral, which is thought to be represented by a Ti +Cl- configuration. The higher charge on the titanium atom shortens the bond. © 2005 Elsevier Inc. All rights reserved.
• Janczyk, A., Walter, S. K., & Ziurys, L. M. (2005). Examining the transition metal hydrosulfides: The pure rotational spectrum of CuSH (X̃ ¹ A′). Chemical Physics Letters, 401(1-3), 211-216.
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  Abstract: The pure rotational spectrum of copper hydrosulfide, CuSH, has been recorded using millimeter/sub-millimeter direct absorption methods. Both copper isotopomers and their deuterated analogs were observed. The molecules were synthesized by the reaction of H 2S or D 2S with copper vapor in a dc discharge. For all four isotopomers, multiple transitions were measured, each exhibiting extensive K a ladder structure and signifying that CuSH is a near-prolate asymmetric top. Rotational parameters were determined for the four species, from which a structure has been derived. The Cu-S-H bond angle was found to be 93°, similar to other metal hydrosulfides and H 2S, rather than CuOH. © 2004 Elsevier B.V. All rights reserved.
• McLamarrah, S. K., Sheridan, P. M., & Ziurys, L. M. (2005). The pure rotational spectrum of CoO(X⁴Δ_i): Identifying the high-spin components. Chemical Physics Letters, 414(4-6), 301-306.
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  Abstract: New measurements of the pure rotational spectrum of the CoO radical in its X4Δi state (v = 0 and v = 1) have been conducted using millimeter-wave direct absorption techniques. CoO was created by the reaction of cobalt vapor and N2O. Spectra arising from the Ω = 3/2 and 1/2 spin levels, both which exhibit Λ-doubling, have been recorded, as well as from the Ω = 7/2 and 5/2 ladders, which have been studied in the past. Rotational, fine structure, Λ-doubling and hyperfine parameters for the v = 0 and v = 1 states have been established from a global analysis of all four spin components. The data suggest a near-by 4Σ state. © 2005 Elsevier B.V. All rights reserved.
• Milam, S. N., Savage, C., Brewster, M. A., Ziurys, L. M., & Wyckoff, S. (2005). The ¹²C/¹³C isotope gradient derived from millimeter transitions of CN: The case for Galactic chemical evolution. Astrophysical Journal Letters, 634(2 I), 1126-1132.
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  Abstract: New measurements of 12C/13C ratios in Galactic molecular clouds have been conducted using the N = 1 → 0 transition of the CN radical. This species is unique in that it has extensive hyperfine structure that can be accurately used to correct for line saturation effects. Combined with the past observations of Savage and coworkers, the ratios derived from CN are the most extensive data set to date for molecular clouds, and they include sources that lie in the range of 0.09-16.41 kpc in distance from the Galactic center (DGC). The ratios derived from CN indicate a gradient with Galactic distance of 12C/13C = 6.01DGC + 12.28. This gradient agrees rather closely with those derived from measurements of CO and H2CO. The least-squares fit to all data points for the three molecules is 12C/13C = 6.21DGC + 18.71. CO, CN, and H2CO are synthesized from quite varied reactions, and any 13C fractionation must follow different pathways for these three species. The relatively good agreement between the 12C/13C ratios of the three molecules, as well as their lack of correlation with gas kinetic temperature, suggests that chemical fractionation and isotope-selective photodissociation both do not play a substantial role in influencing such ratios. Therefore, the 12C/13C gradient found in the Galaxy is a true indicator of Galactic chemical evolution. The apparent discrepancy between the solar system (12C/13C = 89) and local interstellar medium values (12C/13C ≈ 68) of this ratio may be a result of 13C enrichment since the formation of the solar system, as predicted by recent models. © 2005. The American Astronomical Society. All rights reserved.
• Savage, C., & Ziurys, L. M. (2005). A millimeter/submillimeter velocity modulation spectrometer for studies of molecular ions. Review of Scientific Instruments, 76(4).
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  Abstract: A millimeter/submillimeter direct absorption spectrometer has been constructed that employs velocity modulation to selectively detect molecular ions. The instrument consists of a phase-locked Gunn oscillator/Schottky diode multiplier source, a gas absorption cell, and an InSb hot-electron bolometer detector. The gas cell is a single-pass system with two ring-type discharge electrodes at either end, which are connected to an rf power supply. Modulation of the ac discharge at a rate of 50 kHz and phase-sensitive detection at 1f allows for selective observation of molecular ion signals and suppression of absorption from neutral species. The spectrometer can also be used in source-modulated mode, where the signal-to-noise ratio for signals generated in an ac plasma are significantly better than for dc discharges. Combining source modulation with the ac discharge for signal detection and velocity modulation for ion identification provides a powerful technique for molecular ion spectroscopy at millimeter/submillimeter wavelengths. This instrument has been used to measure the pure rotational spectra of C O+, HC O+, and S H+ with better precision than previous studies. © 2005 American Institute of Physics.
• Ziurys, L. M., & Apponi, A. J. (2005). What constitutes spectroscopic proof for the detection of large "hot core" molecules?. Proceedings of the International Astronomical Union, 1, 207-216.
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  Abstract: The presence of large organic species in interstellar gas has important implications for the origin of life and pre-biotic chemistry. Accurate identifications of such molecules, however, are problematic in molecular clouds. There are many reasons for such difficulties. One is that the spectral density is very high in objects where the chemistry is sufficiently complex to produce such species - at least 10 lines per 100 MHz in Sgr B2(N), for example, at 3 mm, at a sensitivity of 10 mK peak-to-peak. Hence, the possibility of chance coincidences is large. Another reason is the presence of many large organic molecules at relatively high temperatures; these large asymmetric tops have vast numbers of favorable transitions under these conditions, including those originating from low-lying vibrational states. Confusion and blending of transitions of one large molecule with those of another add to the risks of an inaccurate identification. A case in point is that of glycolaldehyde, CH 2OHCHO. In order to confirm the identification of this molecule in Sgr B2(N), we searched for its most favorable transitions in the 2 and 3 mm windows, spanning the energy range of ∼10-100 K - a total of 43 individual transitions. Of all these lines, only seven were not heavily blended or contaminated by other molecules, i.e. so-called "clean" features. Emission, however, was visibly detected at 34 of the other transitions, but one transition was clearly absent. The "missing" line corresponds to a weak transition originating in the Ka = 3 ladder, and its absence is consistent with the other detected features. Based on the clean features only, glycolaldehyde has a VLSR = 61.7±1.5 kms-1 and ΔV1/2 = 7.8±1.8 kms-1 with intensities consistently in the range T*R ∼ 20-70 mK. Given these data, the identification of glycolaldehyde is 99.9% secure. A rotational diagram from this data set yields a column density of Ntot ∼ 6 × 1013 cm-2 for CH2OHCHO - roughly a factor of 27 less than that of H2CO. These data illustrate the problems and subtleties in identifying large organic molecules in space. © 2006 International Astronomical Union.
• Flory, M. A., Halfen, D. T., & Ziurys, L. M. (2004). Perturbations in the pure rotational spectrum of CoCl (X ³Φ): A submillimeter study. Journal of Chemical Physics, 121(17), 8385-8392.
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  PMID: 15511159;Abstract: The millimeter/submillimeter-wave spectrum of the CoCl radical (X 3Φ i) has been recorded using direct absorption techniques in the frequency range 340-510 GHz. This work is the first pure rotational study of this molecule. The radical was created by the reaction of Cl 2 with cobalt vapor. Rotational transitions arising from the Ω=4, 3, and 2 spin-orbit components of Co 35Cl have been measured, all of which exhibit hyperfine splittings due to the 59Co nucleus (I=7/2). Transitions arising from the Co 37Cl species were also recorded, as well as those originating in the v = 1, 2, 3, and 4 vibrational states of both isotopomers. The spin-orbit pattern exhibited by the molecule is unusual, with the Ω=3 component significantly shifted relative to the other spin components. In addition, the regular octet hyperfine splittings become distorted above a certain J value for the Ω=3 transitions only. These effects suggest that the molecule is highly perturbed in its ground state, most likely a result of second-order spin-orbit mixing with a nearby isoconfigurational 1Φ 3 state. The complete data set for Co 35Cl and Co 37Cl were fit successfully with a case (a) Hamiltonian but required a large negative spin-spin constant of λ=-7196 GHz and higher order centrifugal distortion corrections to the rotational, spin-orbit, spin-spin, and hyperfine terms. The value of the spin-spin constant suggests that the Ω=3 component is shifted to higher energy and lies near the Ω=2 sublevel. The hyperfine parameters are consistent with a δ 3π 3 electron configuration and indicate that CoCl is more covalent than CoF. © 2004 American Institute of Physics.
• Grotjahn, D. B., Halfen, D. T., Ziurys, L. M., & Cooksy, A. L. (2004). Gas-phase synthesis, submillimeter spectra, and precise structure of monomeric, solvent-free CuCH₃. Journal of the American Chemical Society, 126(39), 12621-12627.
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  PMID: 15453795;Abstract: The most-studied organocopper, methylcopper (CH3Cu), has been synthesized for the first time as a monomer, free of other ligands or coordinated solvent, and detected using millimeter-wave rotational spectroscopy. The molecule was created in the gas phase by the reaction of copper vapor and several different precursors, including CH4 and tetramethylsilane. An obvious symmetric top pattern was observed, indicative of C3v symmetry. For confirmation, rotational spectra of four isotopically substituted species, 65Cu12CH3, 63Cu 12CD3, 63Cu13CH3, and 65Cu13CH3, were recorded as well, following large-scale syntheses of specifically labeled precursors. From this data set, accurate spectroscopic constants and a structure for CH3Cu were derived. The rm(2) geometry shows the shortest alkyl carbon-copper(I) bond length known (1.8809 Å) and a rather large H-C-H angle in the methyl group (109.88°). The measured rotational and distortion constants are well reproduced by QCISD calculations. This study should allow further refinement of theoretical calculations on methylcopper and other organocopper derivatives, which are valuable synthetic intermediates in organic chemistry.
• Halfen, D. T., & Ziurys, L. M. (2004). Precise rest frequencies for AlH and AlD (X ¹Σ⁺): A reassessment of the aluminum hyperfine structure. Astrophysical Journal Letters, 607(1 II), L63-L66.
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  Abstract: The J = 0 → 1 transition of AlH at 377 GHz and the J = 1 → 2 line of AlD at 393 GHz have been recorded using submillimeter direct absorption methods. The two species were created by the reaction of aluminum vapor and H2 or D2 gas in a DC discharge. The 27Al quadrupole hyperfine splittings, which are critical for the astronomical identification of these molecules, were measured for both AlH and AlD. In the case of AlH, the observed hyperfine pattern was not consistent with previous measurements. Values of the hyperfine parameters have thus been revised to be eQq = -48.59 MHz and C1 = 0.306 MHz, which agree very closely with recent ab initio predictions. For AlD, eQq was established to be -48.48 MHz with C2 = 0.156 MHz - the first determination of the hyperfine parameters for the molecule. These measurements should enable viable astronomical searches to be conducted for AlH and AID, presumably with space-borne platforms. Diatomic hydrides containing a cosmically abundant element such as aluminum are fundamental for interstellar and circumstellar chemistry.
• Halfen, D. T., & Ziurys, L. M. (2004). The submillimeter spectrum of CrH and CrD (X⁶Σ ⁺). Astrophysical Journal Letters, 611(1 II), L65-L68.
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  Abstract: The N = 0 → 1 rotational transition of CrH and the N = 1 → 2 transition of CrD have been recorded in their X6L+ ground electronic states using submillimeter direct absorption spectroscopy. Both species were created in a DC discharge by the reaction of chromium metal, vaporized in a Broida-type oven, with H2 or D2. Because of the presence of five unpaired electrons, as well as the proton or deuterium nuclear spin, these transitions exhibit complicated fine structure and hyperfine splittings. The five strongest hyperfine transitions were measured for CrH and are split over a 60 GHz region because of spin-spin and spin-rotation interactions. Seven lines have also been recorded for CrD arising from four spin components. The data have been analyzed with a Hund's case b Hamiltonian, resulting in improved constants for both species. These data are crucial for submillimeter searches for CrH toward interstellar and circumstellar gas. Electronic transitions of CrH have been routinely observed in L dwarf and brown dwarf atmospheres, suggesting its presence in other astronomical regions.
• Higgins, K. J., Freund, S. M., Klemperer, W., Apponi, A. J., & Ziurys, L. M. (2004). The rotational spectrum and dynamical structure of LiOH and LiOD: A combined laboratory and ab initio study. Journal of Chemical Physics, 121(23), 11715-11730.
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  PMID: 15634137;Abstract: Millimeter wave rotational spectroscopy and ab initio calculations are used to explore the potential energy surface of LiOH and LiOD with particular emphasis on the bending states and bending potential. New measurements extend the observed rotational lines to J=7 ← 6 for LiOH and J = 8 ← 7 for LiOD for all bending vibrational states up to (03 30). Rotation-vibration energy levels, geometric expectation values, and dipole moments are calculated using extensive high-level ab initio three-dimensional potential energy and dipole moment surfaces. Agreement between calculation and experiment is superb, with predicted B ν values typically within 0.3%, D values within 0.2%, q 1 values within 0.7%, and dipole moments within 0.9% of experiment. Shifts in B ν values with vibration and isotopic substitution are also well predicted. A combined theoretical and experimental structural analysis establishes the linear equilibrium structure with r e(Li-O) = 1.5776(4) Å and r e(O-H) = 0.949(2) Å. Predicted fundamental vibrational frequencies are ν 1 = 923.2, ν 2 = 318.3, and ν 3 = 3829.8cm -1 for LiOH and ν 1 = 912.9, ν 2 = 245.8, and ν 3 = 2824.2 cm -1 for LiOD. The molecule is extremely nonrigid with respect to angular deformation; the calculated deviation from linearity for the vibrationally averaged structure is 19.0° in the (000) state and 41.9° in the (03 30) state. The calculation not only predicts, in agreement with previous work [P. R. Bunker, P. Jensen, A. Karpfen, and H. Lischka, J. Mol. Spectrosc. 135, 89 (1989)], a change from a linear to a bent minimum energy configuration at elongated Li-O distances, but also a similar change from linear to bent at elongated O-H distances. © 2004 American Institute of Physics.
• Milam, S. N., Savage, C., Ziurys, L. M., & Wyckoff, S. (2004). HCO⁺ observations toward comet Hale-Bopp (C/1995 O1): Ion-molecule chemistry and evidence for a volatile secondary source. Astrophysical Journal Letters, 615(2 I), 1054-1062.
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  Abstract: Several millimeter-wave transitions of HCO+ have been detected toward comet Hale-Bopp (C/1995 O1) using the Arizona Radio Observatory 12 m telescope. The J = 2 → 1 transition at 178 GHz was observed toward the comet nucleus near perihelion on 1997 March 10 and 20, as well as the J = 3 → 2 transition at 268 GHz on 1997 March 9, with angular resolutions of 36″ and 23″, respectively. These data all show a slight velocity shift (∼1.2 km s-1) from the nominal comet velocity, and the J = 3 → 2 profile is asymmetric with a redshifted wing. These differences likely arise from ion acceleration by the solar wind. A rotational diagram analysis of the data yielded a column density of 1.1 × 1012 cm-2 for HCO+ in Hale-Bopp, which corresponds to an average number density of 36 cm-3. The data taken on March 9 show a second velocity component redshifted by 7.0 ± 0.6 km s-1, which is considerably weaker than the main feature and appears to have a counterpart in the HNC, J = 3 → 2 data, observed within an hour of the HCO+ measurements. The velocity difference between the main and secondary emission lines deprojected onto the extended solar radius vector is ∼10 km s-1 for both HCO+ and HNC, and the weak-to-strong line intensity ratios (∼5%) are identical to within observational errors, suggesting a common high-velocity volatile secondary source. A plausible model that may account for the redshifted velocity components is a comoving, localized debris field of submicron refractory grains accelerated by solar radiation pressure located ∼105-10 6 km from the nucleus. The parent material of the weaker redshifted HNC and HCO+ lines may be predominately complex organic polymers. An examination of the production rates for HCO+ suggests that the reaction H2 + CO+ is likely to be an important route to this ion in the outer coma beyond the collisionopause, where it has its peak abundance.
• Savage, C., & Ziurys, L. M. (2004). Ion chemistry in photon-dominated regions: Examining the [HCO ⁺]/[HOC⁺]/[CO^-] chemical network. Astrophysical Journal Letters, 616(2 I), 966-975.
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  Abstract: HOC+ and CO+ have been detected toward two well-known photon-dominated regions (PDRs), S140 and NGC 2023, using the Arizona Radio Observatory 12 m telescope. The J = 1 → 0 transition of HOC+ at 89 GHz and the two spin components of the N = 2 → 1 line of CO+ near 236 GHz were observed, as well as the J = 1 → 0 transitions of H13CO+ and HC18O-. The J = 3 → 2 line of HOC- at 268 GHz was also mapped across the Orion Bar. The [HCO+]/[HOC-] ratios determined in S140 and NGC 2023 were ∼12,408 and 1913, respectively, values indicative of quiescent molecular gas rather than PDR sources, where the abundance of HOC - is thought to be enhanced. However, the beam in both these measurements may contain material from the adjoining molecular cloud, favoring HCO-. Alternatively, the [HCO+]/[HOC+] ratio may vary with Av in PDR regions. The [CO+]/[HOC +] ratio in S140 and NGC 2023, at several positions in the Orion Bar, and in other PDRs, on the other hand, falls uniformly in the range ∼1-10. In addition, the line profiles of CO- and HOC+ in the Orion Bar look remarkably similar. The syntheses of HOC- and CO - appear to be correlated in PDRs, most likely through the common precursor, C+. The reaction of C- and H2O is thought to preferentially create HOC-, as opposed to HCO -, and C+ + OH or O2 leads favorably to CO +.
• Savage, C., Apponi, A. J., & Ziurys, L. M. (2004). Direct measurement of the N = 0 → 1 Transition of SH⁺ (X ³σ^-) by submillimeter velocity modulation spectroscopy. Astrophysical Journal Letters, 608(1 II), L73-L76.
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  Abstract: The N = 0 → 1 transition of SH+ in its 3σ- ground electronic state has been recorded using submillimeter direct absorption/velocity modulation techniques. This molecular ion was created in an alternating current (AC) discharge of H2S and argon, or CH3SH in argon. Four hyperfine lines of the N = 0 → 1 transition were measured: three near 526 GHz and one near 346 GHz, arising from the J = 1 → 2 and J = 1 → 0 spin components, respectively; these four lines contribute 64% of the total intensity of the N = 0 → 1 transition. The measurements have been used to refine the molecular constants of SH +, in particular the fine-structure parameters. Both the transition frequencies and the derived constants are in good agreement with previous laser magnetic resonance data. This study has resulted in very accurate rest frequencies for SH+, which is predicted to be an abundant species in photon-dominated regions.
• Sheridan, P. M., Flory, M. A., & Ziurys, L. M. (2004). Characterizing the later 3d cyanides: The submillimeter spectrum of CoCN(X ³φ _i). Journal of Chemical Physics, 121(17), 8360-8368.
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  PMID: 15511156;Abstract: The pure rotational spectrum of the CoCN radical has been recorded in the frequency range 350-500 GHz using direct absorption techniques. This study is the first spectroscopic observation of this molecule by any experimental technique. Spectra of Co 13CN have been measured as well. These data indicate that this species is linear in its ground electronic state and has the cyanide, as opposed to the isocyanide, geometry. The ground state term has been assigned as 3φ i, based on the measurement of three spin components (Ω=4, 3, and 2) and in analogy to other isovalent cobalt-bearing species. Hyperfine splittings resulting from the 59Co nuclear spin of I=7/2 were observed in every transition, each of which exhibited an octet pattern. For the lowest energy spin component, Ω=4, vibrational satellite features were also identified arising from the first quantum of the Co-C(v 1 = 1) stretch and the v 2 = 1 and v 2 = 2 quanta of the bending mode, which were split by Renner-Teller interactions. The ground state measurements of CoCN were analyzed with a case a β Hamiltonian, establishing rotational, fine structure, and hyperfine parameters. The vibrational and Co 13CN spectra for the Ω=4 component were fit as well. An r 0 structure was also calculated, providing estimates of the Co-C and C-N bond distances, based on the Ω=4 transitions. CoCN is the fourth molecule in the 3d transition metal series to exhibit the linear cyanide structure, along with the Zn, Cu, and Ni analogs. The preference for this geometry, as opposed to the isocyanide form, may indicate a greater degree of covalent bonding in these species. © 2004 American Institute of Physics.
• Highberger, J. L., & Ziurys, L. M. (2003). Detection of MgNC in CRL 618: Tracing metal chemistry with asymptotic giant branch evolution. Astrophysical Journal Letters, 597(2 I), 1065-1069.
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  Abstract: The MgNC radical has been detected toward the circumstellar shell of CRL 618, the first metal-bearing molecule (in the chemist's sense) observed in this proto-planetary nebula. Five rotational transitions of this 2Σ species were measured using the Arizona Radio Observatory (ARO) 12 m and IRAM 30 m telescopes, several which clearly display the characteristic spin-rotation structure. Searches for NaCN, NaCl, AlF, and AlCl in CRL 618, in contrast, proved negative. The line profiles of MgNC in this source, measured at the 30 m, were somewhat U-shaped and showed no evidence of high-velocity wings, indicating that this radical arises from the remnant asymptotic giant branch (AGB) wind. The column density of MgNC in CRL 618 is Ntot = 2.4 × 1012 cm-2, corresponding to a fractional abundance, relative to H2, of f ∼ 5.3 × 10-9. The upper limits for the sodium and aluminum species are typically f < 10-9 to 10-8. The MgNC abundance in CRL 618 is comparable to those measured in CRL 2688 and IRC +10216; the upper limits for the sodium and aluminum compounds are at least a factor of 10 lower in CRL 618 relative to abundances in IRC +10216, but similar to those in CRL 2688. These data suggest that metal-bearing molecules produced by LTE chemistry (NaCl, AlCl, AlF) are destroyed by the events associated with the second stage of AGB mass loss, while radicals such as MgNC survive in the outer envelope for a significant time in the proto-planetary nebula phase.
• Janczyk, A., & Ziurys, L. M. (2003). Studies of metal hydrosulfides III: The millimeter/submillimeter spectrum of BaSH (X̃² A′). Journal of Chemical Physics, 119(20), 10702-10712.
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  Abstract: The pure rotational spectrum of BaSH was measured, proving that this molecule has a bent geometry and Cs symmetry, in analogy to the other alkaline earth hydrosulfides. The barium species appeared to be other slightly more bent than the SrSH and CaSH, with a bond angle near 88°. Perturbations resulting from accidental degeneracies of the spin-rotation levels were observed, shifting certain transitions from the expected pattern. Higher Ka components in BaSD were also perturbed. The spin-rotation constants in the barium species were found to contain large second order contributions.
• Sheridan, P. M., & Ziurys, L. M. (2003). Further studies of 3d transition metal cyanides: The pure rotational spectrum of NiCN (X²Δ_i). Journal of Chemical Physics, 118(14), 6370-6379.
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  Abstract: Measurement of the pure rotational spectrum of NiCN in its 2Δi ground electronic state has enabled the identification of both spin-orbit components of this molecule, as well as new vibronic levels. It has confirmed the linear cyanide structure of this radical, as indicated by optical studies. In the higher lying spin-orbit sublevel, significant lambda-doubling interactions are observed, as is found in NiH(X2Δi).
• Sheridan, P. M., & Ziurys, L. M. (2003). Molecules in high spin states II: The pure rotational spectrum of MnF (X⁷Σ⁺). Chemical Physics Letters, 380(5-6), 632-646.
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  Abstract: The pure rotational spectrum of MnF has been measured in its X 7Σ+ ground state using millimeter/sub-millimeter direct absorption methods. Five and six rotational transitions, respectively, were recorded for this radical in its v=0 and v=1 states in the range 338-630 GHz. MnF was created from SF6 and manganese vapor, produced in a Broida-type oven. The species exhibited a complex pattern where the fine and 55Mn and 19F hyperfine structures are intermixed. Rotational, spin-rotation, spin-spin and hyperfine parameters have been determined for MnF. These constants have been interpreted in terms of bonding and electronic structure in metal fluorides. © 2003 Elsevier B.V. All rights reserved.
• Sheridan, P. M., McLamarrah, S. K., & Ziurys, L. M. (2003). The pure rotational spectrum of TiF (X⁴Φ_r): 3 d transition metal fluorides revisited. Journal of Chemical Physics, 119(18), 9496-9503.
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  Abstract: The first measurement of the pure rotational spectrum of the TiF radical using millimeter/sub-mm direct absorption methods is presented. The given data is modeled using a Hund's case (a) effective Hamiltonian, leading to the determination of rotational, fine structure, and hyperfine parameters. This paper presents the results, interpret the constants and discuss their implications for bonding in 3d transition metal fluorides.
• Sheridan, P. M., Ziurys, L. M., & Hirano, T. (2003). Rotational rest frequencies for FeN (X ²Δ_i) and revised spectroscopic constants for FeC (X ³Δ_i). Astrophysical Journal Letters, 593(2 II), L141-L144.
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  Abstract: The pure rotational spectrum of FeN in its X 2Δ i, ground state has been recorded using millimeter-wave direct absorption techniques in the range 198-525 GHz. New measurements have also been carried out for FeC (X3ΔI), in particular of the Ω = 1 fine-structure component and the 54FeC isotopomer. These molecules were created by the reaction of iron vapor with either CH4 (FeC) or N2 (FeN) in a DC discharge. Eight rotational transitions were recorded for FeN in its lowest-lying spin component, Ω = 5/2, and multiple transitions were measured for FeC in all three of its spin-orbit ladders, as well as for 54FeC (Ω = 3). These data have been analyzed, and precise spectroscopic constants for both radicals have been determined. The fine structure in FeC was found to exhibit an irregular pattern, indicating that higher order spin-orbit perturbations are occurring in this molecule. Although only one spin component was observed for FeN, the bond length established from the Ω = 5/2 data is consistent with a 2Δ ground state, as indicated by theory. Fe-bearing species are relevant to many astrophysical topics, including astrochemistry, dust grains composition, nucleosynthesis, and mass loss from asymptotic giant branch stars.
• Brewster, M. A., & Ziurys, L. M. (2002). Rotational spectroscopy of 3 d transition-metal cyanides: Millimeter-wave studies of ZnCN (X²Σ⁺). Journal of Chemical Physics, 117(10), 4853-4860.
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  Abstract: The rotational spectrum of the ZnCN radical in its ground electronic state was studied by using millimeter/sub-mm direct absorption techniques in the range of 339-543 GHz. The spectroscopic analysis were performed to determine the rotational, spin-rotation and l-type doubling parameters of the (000) and excited vibrational data of the given compounds. The results showed that the metal-carbon bond in ZnCN was weaker with respect to the bonds in CuCN and NiCN.
• Grotjahn, D. B., Brewster, M. A., & Ziurys, L. M. (2002). The first precise molecular structure of a monomeric transition metal cyanide, copper(I) cyanide. Journal of the American Chemical Society, 124(20), 5895-5901.
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  PMID: 12010065;Abstract: Copper(I) cyanide is an important reagent in organic, organometallic, and supramolecular chemistry because of both the copper center and the versatile cyanide ligand. Solid-phase CuCN and many of its derivatives show oligomeric or polymeric structures, a trait shared by other metal cyanides. Often, it is difficult to specify the orientation of the cyano ligand in an X-ray structure. Here the first preparation and precise structure of a monomeric transition metal cyanide is reported. Gas-phase reaction between copper vapor and cyanogen (NCCN) clearly gives CuCN (not CuNC). The precise structure of CuCN so produced is determined by millimeter/submillimeter-wave spectroscopy. Because of the highly efficient synthesis and the presence of significant amounts of two copper isotopes, such strong signals were seen that natural-abundance materials allowed observation of transitions for the four isotopomers 63Cu12C14N, 65Cu12C14N, 63Cu13C14N, and 63Cu12C15N and the determination of ro, r, and rm(2)structures. All data unequivocally show a linear geometry and that the carbon of cyanide is bound to copper with a Cu-C distance of 1.82962(4) Å in the structure, which is likely to be closest to the equilibrium geometry.
• Halfen, D. T., Apponi, A. J., & Ziurys, L. M. (2002). Laboratory detection and pure rotational spectrum of the CaC radical (X³Σ^-). Astrophysical Journal Letters, 577(1 II), L67-L70.
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  Abstract: The calcium carbide radical, CaC, has been observed in the laboratory for the first time using millimeter/submillimeter direct absorption spectroscopy. The species was created in the gas phase by the reaction of calcium vapor and methane under extreme DC discharge conditions. Eleven rotational transitions of CaC in its X3Σ- ground state were recorded in the frequency range 247-536 GHz. Each transition of CaC was found to consist of triplets due to fine-structure interactions that indicate that the ground state is 3Σ-, as opposed to 5Σ -, both of which have been suggested by theory. The data were analyzed in a Hund's case (b) basis, and rotational, spin-spin, and spin-rotation constants have been accurately determined. CaC may be detectable in circumstellar envelopes of asymptotic giant branch stars, in particular those that are carbon-rich.
• Janczyk, A., & Ziurys, L. M. (2002). The millimeter/submillimeter spectrum of LiSH (X̃¹A′): Further investigations of the metal-sulfur bond. Chemical Physics Letters, 365(5-6), 514-524.
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  Abstract: The pure rotational spectrum of LiSH and its 6Li and deuterium isotopomers has been recorded in the region 73-521 GHz using millimeter/sub-millimeter direct absorption techniques. These species were created by the reaction of H2S or D2S and lithium vapor in a dc discharge. Extensive Ka ladder structure was observed for all three isotopomers, indicating that LiSH is a near-prolate asymmetric top with a X̃1A' electronic state. Rotational parameters have been determined for the three species, enabling the calculation of a rm(1) structure. The Li-S-H bond angle was found to be 93°, indicating a high degree of covalent bonding in this molecule. © 2002 Elsevier Science B.V. All rights reserved.
• Largo, A., Redondo, P., Barrientos, C., & Ziurys, L. M. (2002). Structures and stabilities of CaC₃ isomers. Chemical Physics Letters, 355(5-6), 509-516.
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  Abstract: A theoretical study of CaC3 species has been carried out. As a general trend, triplet states are found to be more stable than singlet ones for all isomers. The predicted global minimum is a rhomboidal species, 4t(3B1), whereas another rhomboidal four-membered ring, 3t(3A1), is predicted to lie quite close in energy (about 8.2 kcal/mol higher in energy at the G2(P) level). The corresponding singlet states, 3s(1A1) and 4s(1A1), lie about 11.5 and 13 kcal/mol, respectively, above the predicted global minimum. Therefore our calculations suggest that several species could be accessible to experimental detection. © 2002 Elsevier Science B.V. All rights reserved.
• Savage, C., Apponi, A. J., Ziurys, L. M., & Wyckoff, S. (2002). Galactic ¹²C/¹³C ratios from millimeter-wave observations of interstellar CN. Astrophysical Journal Letters, 578(1 I), 211-223.
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  Abstract: The N = 1 → 0 transitions of 12CN and 13CN(X2∑+) at 113.5 and 108.8 GHz, respectively, have been observed in a sample of 13 Galactic molecular clouds using the Kitt Peak 12 m radio telescope. The objects studied include the Galactic center [SgrB2(OH)], sources in the solar neighborhood such as Orion A and NGC 2024, and various other clouds with and without star formation. Hyperfine structure, arising from the nitrogen nuclear spin, was resolved in the spectra of both species, enabling an accurate determination of the opacity in 12CN. From these measurements, estimates of the 12C/13C isotope ratio were obtained. These values fall in the range 12C/13C ∼ 20-70 and exhibit a noticeable gradient with distance from the Galactic center. In general, the ratios obtained from CN are very similar to those determined from millimeter observations of CO but are consistently lower than those derived from H 2CO. If chemical fractionation is occurring in CN, it is comparable to that in CO. The highest 12C/13C ratios (65 ± 12 and 70 ± 11) were obtained toward two known photon-dominated regions (the Orion Bar and NGC 2024); CN in these two sources may be undergoing some isotope-selective photodissociation. The 12C/13C ratio of 43 ± 7, found in Orion A, is similar to that determined from optical observations of CN toward a nearby source, ζ Ophiuchi, but significantly lower than the average value found in comets (90 ± 10). This difference suggests that substantial enrichment of 13C has occurred during the past 4.6 Gyr in the solar neighborhood.
• Sheridan, P. M., Brewster, M. A., & Ziurys, L. M. (2002). Rotational rest frequencies for CrO (X ⁵Π_r) and CrN (X ⁴∑^-). Astrophysical Journal Letters, 576(2 I), 1108-1114.
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  Abstract: The pure rotational spectra of CrO (X 5Πr) and CrN (X 4∑-) have been recorded using millimeter/sub-millimeter-wave spectroscopy in the frequency range 248-636 GHz. These radicals were created by the reaction of chromium vapor, produced in a Broida-type oven, with N2O or NH3 under DC discharge conditions. For CrO, 12 rotational transitions were recorded, in which up to five spin-orbit components were observed - the first measurement of the pure rotational spectrum of a molecule in a 5Π electronic state. Nine rotational transitions were recorded for CrN; here all four spin components were measured in every transition. The data obtained for both radicals were analyzed using an appropriate effective Hamiltonian. The resulting spectro-scopic parameters of these species were determined to high precision, including those related to fine structure and lambda doubling. This work will enable radioastronomical searches for CrN and CrO to be carried out. CrO has already been observed in the optical spectra of stellar atmospheres.
• Sheridan, P. M., Xin, J., Ziurys, L. M., Beaton, S. A., Kermode, S. M., & Brown, J. M. (2002). The pure rotational spectrum of NaC in its X ⁴Σ^- state: Observation and interpretation. Journal of Chemical Physics, 116(13), 5544-5550.
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  Abstract: The pure rotational spectrum of NaC in its X 4σ- state was recorded using millimeter/submillimeter-wave absorption spectroscopy. NaC was synthesized from the reaction of sodium vapor with methane gas in a dc discharge. Phase-locked Gunn oscillators and Schottky diode multipliers were used in combination to produce radiation in the 65-540 GHz range. Analysis of the rotational spectrum showed the development of uncertainty in the determination of spin-spin parameter in 4σ states.
• Thompsen, J. M., Brewster, M. A., & Ziurys, L. M. (2002). Molecules in high spin states: The millimeter and submillimeter spectrum of the MnS radical (X ⁶Σ⁺). Journal of Chemical Physics, 116(23), 10212-10220.
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  Abstract: The pure rotational spectrum of MnS (v = 0) in its X6σ+ ground state was discussed using millimeter and submillimeter direct absorption techniques. MnS was synthesized in the gas phase by the reaction of manganese vapor and CS2 in a high-temperature Borida-type oven and fourteen rotational transitions were measured for this radical. The analysis showed that MnS was more covalent than MnO but more ionic than MnH.
• Ziurys, L. M., Savage, C., Highberger, J. L., Apponi, A. J., Guélin, M., & Cernicharo, J. (2002). More metal cyanide species: Detection of A1NC (X¹ ∑ ⁺) Toward IRC + 10216. Astrophysical Journal Letters, 564(1 II), L45-L48.
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  Abstract: A new metal-containing species, A1NC, has been detected toward the circumstellar envelope of the late-type carbon star IRC + 10216, using the IRAM 30 m telescope. The J = 11 → 10, 12 → 11, and 13 → 12 rotational transitions at 2 mm and the J = 18 → 17 and J = 21 → 20 transitions at 1.2 mm of this linear, closed-shell molecule were observed in this object. The line profiles appear U-shaped, indicating a source ≃20″, and the horn-to-center ratios suggest a shell-like distribution. In contrast, the other two Al-bearing molecules previously detected, A1F and A1C1, exist exclusively near the stellar photosphere. Modeling of the detected transitions, assuming a spherical-shell distribution, indicates a column density of Ntot ∼9 × 1011 cm-2 and a fractional abundance relative to H2 of ∼ 3 × 10-10 for A1NC. A rotational temperature of Trot ∼ 60 K was also derived for this molecule, suggesting that shock waves may be synthesizing A1NC in the outer envelope. This species is the fourth metal cyanide/isocyanide compound discovered in this object, along with MgNC, MgCN, and NaCN. These data suggest that cyanide/isocyanide species are the major molecular carriers of metals in circumstellar gas.
• Brewster, M. A., & Ziurys, L. M. (2001). The millimeter-wave spectrum of NiC (Χ¹Σ⁺) and CoC (Χ²Σ⁺). Astrophysical Journal Letters, 559(2 PART 2), L163-L166.
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  Abstract: The pure rotational spectra of two metal carbide species, NiC (Χ1Σ+) and CoC (Χ2Σ+), have been measured in the laboratory using millimeter/submillimeter direct absorption methods. The molecules were created by reacting metal vapor with CH4 in a DC discharge. Four rotational transitions of CoC were recorded, each consisting of 16 hyperfine components arising from the cobalt nuclear spin of I = 7/2. Multiple transitions of the two most abundant nickel isotopomers, 58NiC and 60NiC, were additionally measured. The spectra were analyzed using the appropriate Hamiltonian and spectroscopic constants accurately determined. For CoC, this study included a complex hyperfine analysis of the magnetic, electric quadrupole, and nuclear spin-rotation terms. Cobalt and nickel are iron peak elements that may be produced via neutron capture processes in asymptotic giant branch stars. Dredge-up events mix these elements to the stellar surface, where they are incorporated into the expanding stellar envelope. CoC and NiC offer a means to trace these elements in carbon-rich circumstellar shells.
• Brewster, M. A., & Ziurys, L. M. (2001). The millimeter/sub-millimeter spectrum of the LiS radical in its ²Π_i ground state. Chemical Physics Letters, 349(3-4), 249-256.
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  Abstract: The pure rotational spectrum of LiS (X2Πi) has been recorded in the v=0 and v=1 states in the region 130-540 GHz using millimeter/sub-millimeter direct absorption methods. This radical was synthesized from lithium vapor and CS2 in a DC discharge. Transitions arising from the two orbit components were measured, both which exhibited lambda-doubling and, for the Ω=1/2 ladder, hyperfine interactions. Rotational, lambda-doubling, and hyperfine parameters have subsequently been determined. These data prove unambiguously that the ground state of LiS is 2Πi and suggest that the A2Σ+ state lies ~4300cm-1 higher in energy. The bonding in this radical appears to be predominantly ionic. © 2001 Elsevier Science B.V.
• Brewster, M. A., & Ziurys, L. M. (2001). The pure rotational spectrum of KH (X¹Σ⁺): Quadrupole coupling in alkali hydrides. Astrophysical Journal Letters, 559(2 PART 1), 1190-1193.
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  Abstract: The pure rotational spectrum of KH (X1Σ+) has been recorded using millimeter/submillimeter direct absorption techniques. The species was created by the reaction of potassium vapor and H2 in a d.c. discharge. The J = 0 → 1 and 1 → 2 transitions were measured near 202 and 404 GHz, and electric quadrupole splittings were resolved in the J = 0 → 1 line and partly resolved in the other transition. For comparison, the quadrupole structure in the J = 0 → 1 transition of NaH (X1Σ+) was also recorded. Very accurate rotational and quadrupole hyperfine constants were determined for KH, and eqQ was established for NaH as well. Diatomic hydride species are the building blocks for interstellar chemistry in both dense and diffuse gas. Knowledge of the rest frequencies of KH will enable its detection in such objects.
• Grotjahn, D. B., Sheridan, P. M., Jihad, I. A., & Ziurys, L. M. (2001). First synthesis and structural determination of a monomeric, unsolvated lithium amide, LiNH₂. Journal of the American Chemical Society, 123(23), 5489-5494.
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  PMID: 11389631;Abstract: Alkali metal amides typically aggregate in solution and the solid phase, and even in the gas phase. In addition, even in the few known monomeric structures, the coordination number of the alkali metal is raised by binding of Lewis-basic solvent molecules, with concomitant change in structure. In contrast, the simplest lithium amide LiNH2 has never been made in a monomeric form, even though its structure has been theoretically predicted several times. Here, the first experimental structural data for a monomeric, unsolvated lithium amide are determined using a combination of gas-phase synthesis and millimeter/submillimeter-wave spectroscopy. All data point to a planar structure for LiNH2. The ro structure of LiNH2 has a Li-N distance of 1.736(3) Å, an N-H distance of 1.022(3) Å, and a H-N-H angle of 106.9(1)°. These results are compared with theoretical predictions for LiNH2, and experimental data for oligomeric, solid-phase samples, which could not resolve the question of whether LiNH2 is planar or not. In addition, comparisons are made with revised gas-phase and solid-phase data and calculated structures of NaNH2.
• Halfen, D. T., Apponi, A. J., & Ziurys, L. M. (2001). Evaluating the N/O chemical network: The distribution of N₂O and NO in the Sagittarius B2 complex. Astrophysical Journal Letters, 561(1 PART 1), 244-253.
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  Abstract: Mapping observations of the J = 6 → 5 transition of N2O and the Π+1/2, J = 3/2 → 1/2 line of NO in the 2 mm band toward the core region of the Sagittarius B2 complex have been carried out using the Kitt Peak 12 m telescope. Emission from NO was found to be extended over a region 2′ × 5′ in size that includes the Sgr B2 (N), Sgr B2 (M), and Sgr B2 (OH) positions, very similar to the distribution found for HNO. In contrast, N2O emission was confined to a source approximately 1′ in extent, slightly elongated in the north-south direction and centered on the Sgr B2 (N) core. A virtually identical distribution was found for the JKτ = 140 → 14-1 E transition of methanol, which lies 255 K above ground state and samples very hot gas. Excitation conditions are favorable for the J = 6 → 5 line of N2O over the entire NO region; hence, the confined nature of this species is a result of chemistry. The J = 3 → 2 and J = 9 → 8 lines of N2O at 75 and 226 GHz, respectively, were also detected at Sgr B2 (N). Combined with the J = 6 → 5 data, these transitions indicate a column density for this molecule of Ntot ∼ 1.5 × 1015 cm-2 at this position and an abundance of f(N2O/H2) ∼ 1.5 × 10-9. This fractional abundance is almost 2 orders of magnitude higher than predicted by low-temperature chemical models. The N2O observations suggest that this molecule is preferentially formed in high-temperature gas; a likely mechanism is the neutral-neutral reaction NO + NH → N2O + H, which has an appreciable rate only at T > 125 K. The column density of NO found over the Sgr B2 cloud was Ntot ∼ (0.8-1.5) × 1016 cm-2, corresponding to a fractional abundance of f(NO/H2) ∼ (0.8-1.5) × 10-8, which is about 1 order of magnitude less than model predictions. The similar distributions of NO and HNO suggest a chemical connection. It is likely that the major route to HNO is from NO via the ion-molecule process NO + HNO+ → NO+ + HNO, which occurs readily at low temperatures. The NO molecule thus appears to be the main precursor species in the N/O chemical network.
• Halfen, D. T., Apponi, A. J., Thompsen, J. M., & Ziurys, L. M. (2001). The pure rotational spectra of SrSH (X̃ ²A′) and SrS (X ¹∑⁺): Further studies in alkaline-earth bonding. Journal of Chemical Physics, 115(24), 11131-11138.
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  Abstract: Millimeter/submillimeter-wave direct absorption techinques were used to measure the pure rotational spectrum of the SrSH radical in its ground electronic and vibrational states. The study of thirteen transitions of SrS in each of its ground, first and second states was also presented. Spectroscopic parameters were determined for all three species, including spin-rotation terms for the strontium hydrosulfides by analyzing the data.
• Sheridan, P. M., & Ziurys, L. M. (2001). Trends in the alkaline-earth amide series: The millimetre-wave spectrum of MgNH₂ and MgND₂ (X̃²A₁). Canadian Journal of Physics, 79(2-3), 409-421.
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  Abstract: The pure rotational spectra of MgNH2 (X̃2A1) and its deuterium isotopomer have been recorded using millimetre/sub-millimetre wave direct absorption techniques. Both species were synthesized by the reaction of magnesium vapor and either NH3 or ND3 in a dc discharge. Twelve rotational transitions were measured for MgNH2, and eight transitions were observed for MgND2, both in the range 120-530 GHz. Asymmetry components with Ka = 0-5,7, and sometimes 6, were measured for nearly every transition. Rotational, centrifugal distortion, and spin-rotation parameters have been accurately determined for both molecules, as well as an r0 structure for magnesium amide. The data indicate that MgNH2 is a planar molecule with C2v symmetry, similar to CaNH2 and SrNH2, and does not undergo inversion. However, there appears to be subtle differences between MgNH2 and its calcium and strontium analogs. Magnesium amide, for example, has a significantly larger H-N-H bond angle than CaNH2 and SrNH2. In addition, the spin-rotation constants indicate slightly more in-plane p character for the unpaired electron in this molecule relative to that in calcium or strontium amide. Such differences may result from more covalent character in the bonding of MgNH2 in comparison to the heavier alkaline-earth amide species.
• Thompsen, J. M., & Ziurys, L. M. (2001). Transition metal sulfide studies: The pure rotational spectrum of the CuS radical (X²Π_i). Chemical Physics Letters, 344(1-2), 75-84.
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  Abstract: The pure rotational spectrum of CuS in its X2Πi ground state has been recorded using direct absorption techniques in the range 140-540 GHz. This radical was produced by the reaction of copper vapour with CS2. Both the v=0 and v=1 states of 63CuS were observed, as well as the 65CuS(v=0) isotopomer. 25, 13, and 8 rotational transitions were recorded for these three species, respectively. Both the Ω=1/2 and Ω=3/2 spin-orbit ladders were observed. Accurate rotational, spin-orbit, and lambda-doubling constants were subsequently determined for these molecules. These data suggest that 3d-sulfides have subtle bonding differences relative to the corresponding 3d-oxides. © 2001 Elsevier Science B.V.
• Brewster, M. A., & Ziurys, L. M. (2000). The pure rotational spectrum of CaNH₂ and CaND₂ (X̃²A₁): Additional proof of planarity. Journal of Chemical Physics, 113(8), 3141-3149.
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  Abstract: The pure rotational spectrum of CaNH2 in its X̃2A1 ground electronic state has been recorded using millimeter/submillimeter direct absorption methods in the frequency range 320-537 GHz as well as that of CaND2. The species were created by Broida-oven techniques. Eleven rotational transitions were observed arising from the v=0 and v6=1 states of CaNH2, and eight transitions were recorded for the v3=1 and v4=1 levels. For CaND2, eight transitions (v=0) were also measured. For the majority of these transitions, Ka doublets corresponding to Ka=0-5 were observed and fine structure splittings were resolved in every component. These spectra were analyzed using an S-reduced Hamiltonian; rotational, centrifugal distortion, and spin-rotation parameters were determined for CaNH2, CaND2, and the three observed vibrationally excited states. An r0 structure has also been calculated. The data are consistent with calcium amide being a planar molecule with C2v symmetry and having predominately ionic bonding, as indicated by previous optical studies. © 2000 American Institute of Physics.
• Grotjahn, D. B., Pesch, T. C., Brewster, M. A., & Ziurys, L. M. (2000). Synthesis of CH₃K in the gas phase: Structural and mechanistic trends for monomeric, unsolvated CH₃M and HCCM (M = Li, Na, K). Journal of the American Chemical Society, 122(19), 4735-4741.
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  Abstract: Monomeric, solvent-free CH3K has been made in the gas phase and its precise structure determined by millimeter/submillimeter spectroscopy, from which the following parameters were deduced: C-K and C-H bond lengths are 2.633 and 1 135 Å, respectively, and the H-C-H angle is 107.0°. The structure completes a series with those reported for CH3Na and CH3Li, showing the expected decrease in metal-carbon bond length (2.633 to 2.299 to 1.961 Å) ascending the periodic table, but little change in the H-C-H bond angles, which are all near 107°. The latter observation on these simple monomeric species clearly differs from the range of 104.8-108.2°reported for oligomeric CH3M samples in the solid phase, which feature several metal- carbon contacts, showing the importance of measurements on monomeric species. Synthetic details for the methyl compounds and HCCM (M = Li, Na, K) are also discussed. Preparation of HCCLi from HCCBr and Li vapor produced LiBr but possible intermediate radical HCC· was not detected, suggesting synchronous reduction of the C-Br bond. The linear structure of HCCM is contrasted with nonlinear structures of LiCCLi (predicted theoretically), NaCN, and KCN, using Coulombic arguments to explain the different molecular geometries.
• Sheridan, P. M., & Ziurys, L. M. (2000). Laboratory detection of the MgNH2 radical (X2A1). Astrophysical Journal Letters, 540(1 PART 2), L61-L64.
• Thompsen, J. M., Sheridan, P. M., & Ziurys, L. M. (2000). Rotational spectroscopy of the SrNH₂ and SrND₂ radicals ( X̃²A₁ ). Chemical Physics Letters, 330(3-4), 373-382.
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  Abstract: The pure rotational spectrum of the SrNH2 radical in its X̃2A1 state has been recorded using sub-millimeter direct absorption techniques in the range 225-540 GHz. Measurements of SrND2 have also been conducted. Both molecules were produced by the reaction of metal vapor and NH3 or ND3. Fourteen and fifteen rotational transitions were recorded for SrNH2 and SrND2, respectively. Asymmetry doublets for Ka=0 through 5 or 6, as well as fine structure splittings, were observed in every transition. From these data, spectroscopic constants have been determined, as well as an r0-structure. This study provides additional evidence that SrNH2 is planar with ionic bonding. © 2000 Elsevier Science B.V.
• Wyckoff, S., Kleine, M., Peterson, B. A., Wehinger, P. A., & Ziurys, L. M. (2000). Carbon isotope abundances in comets. Astrophysical Journal Letters, 535(2 PART 1), 991-999.
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  Abstract: Rotational lines of 13C14N have been identified in high-resolution (λ/△λ ∼ 60,000) echelle spectra of the CN B2Σ+ - X2Σ+ (0-0) band in three comets. The 12C/13C abundance ratios determined using a full fluorescence excitation model for comets Levy (C/1990 K1), Austin (C/1989 X1), and Okazaki-Levy-Rudenko (C/1989 XIX) are 90 ±10, 85 ±20, and 93 ± 20, respectively, consistent with the solar system ratio, 90. A lower limit for the nitrogen isotope ratio, 12C14N/12C15N ≳ 200, found for comet Levy is consistent with previous comet measurements and the solar system value, 272. The mean CN carbon isotope ratio in the five comets measured to date is 12C14N/12C15N = 90 ± 10, and the mean for the three molecular species C2, HCN, and CN measured in nine comets is 101 ± 15. Consistency of the cometary carbon isotope ratios with the bulk solar system value indicates (1) chemical homogeneity in the outer protosolar nebula, (2) minimal isotopic fractionation in the protosolar precursor molecular cloud, and (3) that comets formed coevally with the solar system. The 14% difference between the solar system (90) and the present solar neighborhood interstellar 12C/13C ratio (77 ±7) may be indicative of significant Galactic 13C enrichment over the past 4.6 Gyr. However, even though models can match to within a factor of 2 the solar system abundances, including the carbon isotope ratio, other evidence suggests that simple homogeneous Galactic evolution models may not be adequate to explain detailed stellar and interstellar abundances in the Galaxy.
• Xin, J., Brewster, M. A., & Ziurys, L. M. (2000). The pure rotational spectrum of gas-phase NaNH₂ (X̃¹A₁). Astrophysical Journal Letters, 530(1 PART 1), 323-328.
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  Abstract: The pure rotational spectrum of NaNH2 (X̃1A1) has been recorded using millimeter/submillimeter direct absorption techniques. This study is the first gas-phase detection of this molecule in the laboratory. NaNH2 was generated by the reaction of sodium vapor and NH3 in the presence of a DC discharge. The Ka = 0, 1, 2, 3, 4, and 5 components in 10 separate rotational transitions were measured, identifying the molecule as a planar, near-prolate asymmetric top with C2v, symmetry. The data were analyzed using an S-reduced Hamiltonian, and rotational constants A, B, and C were determined, as well as various centrifugal distortion parameters. An r0 structure was additionally calculated for the molecule. NaNH2 may be produced in circumstellar or interstellar gas via the radiative association reaction Na+ + NH3 → NaNH+3 + hv, followed by dissociative electron recombination. Theoretical calculations by Petrie suggest this pathway may be sufficiently fast to synthesize detectable concentrations of NaNH2.
• Apponi, A. J., Anderson, M. A., & Ziurys, L. M. (1999). High resolution spectroscopy of MgOH (X ²Σ⁺) in its V₂ mode: Further evidence for quasilinearity. Journal of Chemical Physics, 111(24), 10919-10925.
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  Abstract: Pure rotational spectra of the MgOH and MgOD radicals have been recorded in the v2 bending vibration of their X 2Σ+ ground electronic states using millimeter-wave direct absorption spectroscopy. Multiple rotational transitions arising from the v12= 11, 22, 20, 31, 33, 42, and 44 substates have been measured in the frequency range 240-520 GHz for these species. Both the spin-rotation and l-type doubling interactions have been resolved in the spectra. The complete data sets for MgOH and MgOD have been analyzed using a linear model for the Hamiltonian which takes into account higher order (l=±4) l-type interactions. The global analyses were adequate, but anomalous behavior was apparent in both molecules. In particular, the Bv vs v2 relation was found to be highly nonlinear, large variations in the l-type doubling constant q were observed with vibrational level, and r0, rs, and r̃e structures determined differed substantially. Such findings suggest that MgOH is highly quasilinear, comparable to HNCO. The competition between ionic and covalent bonding is therefore becoming apparent in the lighter alkaline earth hydroxide species. © 1999 American Institute of Physics.
• Apponi, A. J., Pesch, T. C., & Ziurys, L. M. (1999). Detection of HOC⁺ toward the orion bar and M17-SW: Enhanced abundances in photon-dominated regions?. Astrophysical Journal Letters, 519(1 PART 2), L89-L92.
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  Abstract: New measurements of HOC+ emission have been carried out toward several photon-dominated regions using the National Radio Astronomy Observatory 12 m telescope. Toward the Orion bar, the J = 1 → 0, 2 → 1, and 3 → 2 transitions of HOC+ at 89, 179, and 268 GHz were detected, as well as the J = 1 → 0 line in M17-SW. In conjunction with observations of HC18O+, [HCO+]/[HOC+] abundance ratios have been established in these objects. Toward M17-SW, a ratio of ∼2260 was found. In the Orion bar, on the other hand, this ratio was determined to be [HCO+]/[HOC+] ∼ 270, both from J = 1 → 0 and J = 2 → 1 measurements - the lowest ratio thus far found in the Galaxy, and remarkably different from the value of 1800 found in nearby OMC-1. Moreover, the fractional abundance of HOC+ was found to be f ≳ 7 × 10-12 in this source, the highest value yet observed for this molecular ion. The Orion bar observations suggest that the abundance of HOC+ is enhanced relative to HCO+ because of the unique chemistry of photon-dominated regions.
• Xin, J., & Ziurys, L. M. (1999). Gas phase spectroscopy of alkali carbides: The pure rotational spectrum of KC (X ⁴Σ^-). Journal of Chemical Physics, 110(10), 4797-4802.
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  Abstract: The pure rotational spectrum of the KC radical in its X 4Σ- ground state has been recorded using millimeter/submillimeter direct absorption spectroscopy. This study is the first gas phase observation of potassium carbide, and of any alkali metal carbide species. The molecule was produced under d.c. discharge conditions by the reaction of potassium vapor and CH4; the vapor was generated in a Broida-type oven. Eleven rotational transitions were measured for KC in the frequency range 344-515 GHz; fine structure was resolved in every transition, which consisted of a quartet pattern. The data were analyzed using nonlinear least-squares methods in a Hund's case (b) basis, and rotational and fine structure parameters were accurately determined. The third-order contribution to the spin-rotation term was not found necessary for the data fit, although it has been suggested for states of quartet multiplicity and higher. The spin-spin interactions in KC appear to have a significant direct dipolar component. The bond length and electron configuration in KC have also been established, which suggest some covalent character to its bonding. © 1999 American Institute of Physics.
• Xin, J., & Ziurys, L. M. (1999). Structural studies of alkali methylidyne radicals: High resolution spectroscopy of NaCH and KCH (X̃³Σ^-). Journal of Chemical Physics, 110(7), 3360-3367.
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  Abstract: High resolution spectroscopic measurements have been carried out for alkali methylidyne radicals. The pure rotational spectra of NaCH and KCH, along with their deuterium isotopomers, have been recorded in the frequency range 328-529 GHz using millimeter/submillimeter direct absorption techniques. These molecules were created in a dc discharge by the reaction of metal vapor and CH4 or CD4. These data indicate that KCH and NaCH are linear molecules with 3Σ- ground electronic states arising from a π2 configuration. Spectroscopic constants for KCH and NaCH have been determined from the data, including rotational, spin-spin, and spin-rotation parameters, as well as bond lengths. In comparison with other alkali and transition metal-bearing molecules, these results suggest some degree of covalent bonding in the alkali methylidynes, with carbon atom undergoing sp hybridization. © 1999 American Institute of Physics.
• Ziurys, L. M., Savage, C., Brewster, M. A., Apponi, A. J., Pesch, T. C., & Wyckoff, S. (1999). Cyanide chemistry in comet Hale-Bopp (C/1995 O1). Astrophysical Journal Letters, 527(1 PART 2), L67-L71.
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  Abstract: Observations of comet Hale-Bopp (C/1995 O1) have been carried out near perihelion (1997 March) at millimeter wavelengths using the NRAO 12 m telescope. The J = 1 → 0, 2 → 1, and 3 → 2 lines of HCN at 88, 177, and 265 GHz were measured in the comet as well as the J = 3 → 2 lines of H13CN, HC15N, and HNC. The N = 2 → 1 transition of CN near 226 GHz was also detected, and an upper limit was obtained for the J = 2 → 1 line of HCNH+. From the measurements, column densities and production rates have been estimated. A column density ratio of [HCN]/[HNC] = 7 ± 1 was observed near perihelion, while it was found that [HCN]/[HCNH+] ≳ 1. The production rates at perihelion for HCN and CN were estimated to be Q(HCN) ∼ 1 × 1028 s-1 and Q(CN) ∼ 2.6 × 1027 s-1, respectively, resulting in a ratio of [HCN]/[CN] ≃ 3. Consequently, HCN is sufficiently abundant to be the parent molecule of CN in Hale-Bopp, and HCNH+ could be a source of HNC. Finally, carbon and nitrogen isotope ratios of 12C/13C = 109 ± 22 and 14N/15N = 330 ± 98 were obtained from HCN measurements, in agreement with previous values obtained from J = 4 → 3 data. Such ratios suggest that comet Hale-Bopp formed coevally with the solar system.
• Allen, M. D., Pesch, T. C., Robinson, J. S., Apponi, A. J., Grotjahn, D. B., & Ziurys, L. M. (1998). The pure rotational spectrum of LiCH₃ ( X̃ ¹A ). Chemical Physics Letters, 293(5-6), 397-404.
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  Abstract: The pure rotational spectrum of lithium monomethyl, LiCH3, in its X̃ 1A ground electronic state has been measured using millimeter/sub-millimeter direct absorption techniques. Spectra of LiCD3 and 6LiCH3 have been recorded as well. These species were synthesized in the gas phase by the reaction of lithium vapor, produced in a Broida-type oven, and (CH3)4Sn, (CH3)2Hg or CH3I. Transitions were recorded in the 90-505 GHz range for J=2←1 to J=11←10 and K=0 up to K=10. Rotational and centrifugal distortion constants have been determined for each isotopomer, as well as an ro structure for LiCH3.
• Apponi, A. J., Brewster, M. A., & Ziurys, L. M. (1998). Rotational spectroscopy of LiCCH ( X̃ ¹Σ ) in its ground and v₅ vibrational states. Chemical Physics Letters, 298(1-3), 161-169.
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  Abstract: The pure rotational spectrum of LiCCH (X̃ 1Σ) in its ground and v5 vibrational states has been recorded using direct absorption, millimeter/sub-millimeter spectroscopy in the range of 105-538 GHz. For the main isotopomer, 21 transitions were measured for the ground state and 10 transitions each for the excited levels v5=1, 2, and 3, where ℓ-type doubling was resolved. Several transitions were also recorded for 6LiCCH, Li13CCH, LiC13CH, and LiCCD. All were observed in their natural abundances except for LiCCD. Rotational, ℓ-type doubling and vibration-rotation constants were determined for LiCCH, as well as rs and ro structures.
• Grotjahn, D. B., Apponi, A. J., Brewster, M. A., Xin, J., & Ziurys, L. M. (1998). Structures of solvent-free, monomeric liCCH, naCCH, and KCCH. Angewandte Chemie - International Edition, 37(19), 2678-2681.
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  Abstract: The simplest alkali metal acetylides MCCH were made in the gas phase for the first time (see drawing), and their bond lengths were determined by millimeter/submillimeter spectroscopy of their isotopomers. The M-C bond lengths r(CM) are the shortest known for organoalkali metal compounds. In the case of LiCCH, the experimentally determined Li-C distance of 1.888 Å has an estimated accuracy of ±0.0005 Å, which should allow a rigorous test of theoretical methods.
• Xin, J., & Ziurys, L. M. (1998). Laboratory detection and pure rotational spectrum of the NaCH radical (X̃ ³Σ^-). Astrophysical Journal Letters, 508(1 PART II), L109-L112.
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  Abstract: The sodium methylidyne radical, NaCH, has been detected in the laboratory for the first time using submillimeter direct absorption spectroscopy. The species was created in the gas phase in a DC discharge by the reaction of sodium vapor and CH4. Nine rotational transitions of this molecule were recorded in the frequency range 339-520 GHz, and five transitions of its deuterium isotopomer, NaCD. Each transition of sodium methylidyne was found to consist of triplets resulting from fine structure interactions, identifying the ground state of the molecule to be X̃ 3Σ-. The data were analyzed with a 3Σ- Hamiltonian in a case b basis, and rotational, spin-spin, and spin-rotation constants have been accurately determined. NaCH may be formed in the envelopes of AGB stars from the reaction of sodium with photodissociation products of methane. © 1998. The American Astronomical Society. All rights reserved.
• Xin, J., Robinson, J. S., Apponi, A. J., & Ziurys, L. M. (1998). High resolution spectroscopy of BaCH₃(X̃²A₁): Fine and hyperfine structure analysis. Journal of Chemical Physics, 108(7), 2703-2711.
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  Abstract: The pure rotational spectrum of BaCH3(X̃2A1) in its ground vibrational state has been recorded using millimeter/submillimeter direct absorption techniques, the first spectroscopic information obtained for this molecule. The radical was created using Broida-type oven/d.c. discharge methods by the reaction of barium vapor and Sn(CH3)4. Twenty-eight rotational transitions of the main isotopomer 138BaCH3 were recorded, as well as five for 136BaCH3 and three for the 137BaCH3 species. Being a prolate symmetric top, K ladder structure was observed in all transitions for BaCH3, as well as fine structure splittings which arise from the unpaired electron in the molecule. For the 137Ba isotopomer, hyperfine interactions were also resolved, arising from the spin of the barium nucleus. The complete data set has been analyzed with a 2A Hamiltonian, and rotational, spin-rotational, and magnetic hyperfine/nuclear quadrupole parameters accurately determined. The fine and hyperfine structure constants established from this study suggest a predominantly ionic bond for BaCH3, but with a considerable covalent component. Structural parameters for BaCH3 derived in this work are consistent with those of other alkaline earth monomethyl species. © 1998 American Institute of Physics.
• Allen, M. D., & Ziurys, L. M. (1997). Millimeter-wave spectroscopy of FeF (X ⁶Δ_i): Rotational analysis and bonding study. Journal of Chemical Physics, 106(9), 3494-3503.
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  Abstract: The pure rotational spectrum of the FeF radical in its 6Δi ground electronic state has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from all six spin orbit components have been observed in the v=0, 1. and 2 vibiational levels of 56FeF, the main isotopic species, and also in the less abundant 54Fe isotopomer. Hyperfine splittings, arising from the 19F nuclear spin of I=1/2, were resolved in the majority of transitions recorded, and lambda-doubling interactions were observed in the Ω=3/2. 1/2. and -1/2 spin-orbit ladders. The complete data set has been analyzed using a 6Δ Hamiltonian, and rotational, spin-orbit, spin-spin lambda-doubling, and hyperfine constants determined. This study has conclusively demonstrated that the ground electronic state of FeF is 6Δi. It also suggests that FeF has more covalent character to its bonding than alkaline earth or alkali metal counterparts. © 1997 Amencan Institute of Physics.
• Allen, M. D., Li, B. Z., & Ziurys, L. M. (1997). A millimeter/sub-millimeter-wave spectroscopic study of the FeCl radical (X ⁶Δ_i). Chemical Physics Letters, 270(5-6), 517-526.
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  Abstract: Pure rotational spectroscopy of the FeCl radical (X 6Δi) has been carried out using millimeter/sub-millimeter direct absorption techniques. The species was created by the reaction of chlorine with iron vapor. All six spin - orbit components were observed in the majority of the twenty-one rotational transitions recorded. Chlorine hyperfine structure was resolved in the Ω = 9/2 and 7/2 components, and lambda-type doubling observed in the Ω = 3/2, 1/2, and - 1/2 ladders. The data were analyzed with a 6Δ Hamiltonian, and rotational, fine structure, lambda-doubling, and hyperfine parameters determined. The hyperfine and lambda-doubling interactions in FeCl appear to be different from those in the FeF radical.
• Apponi, A. J., & Ziurys, L. M. (1997). New observations of the [HCO⁺]/[HOC⁺] ratio in dense molecular clouds. Astrophysical Journal Letters, 481(2 PART I), 800-808.
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  Abstract: New measurements of the millimeter-wave transitions of HOC+ toward dense molecular clouds have been carried out using the NRAO 12 m telescope. The J = 1 → 0 transition of HOC+ at 89 GHz has been detected for the first time toward DR21 (OH), W51M, W3 (OH), NGC 7538, Orion (3N, 1E), NGC 2024, and G34.3. The J = 2 → 1 and J = 3 → 2 lines at 179 GHz and 268 GHz have also been observed in W51 and Orion KL. In conjunction with past observations of HOC+ toward Orion KL and SgrB2 (OH) by Ziurys & Apponi, these data confirm the presence of this ion in the interstellar medium. The column densities of HOC+ were found to be Niot ∼ (7 × 1010)-(3 × 1012) cm-2, which correspond to fractional abundances of f∼(2 × 10-13)-(3 × 10-12) relative to H2. Observations of the J = 1 → 0 transition of HC18O+ at 85 GHz have also been carried out, resulting in [HCO+]/[HOC+] ratios of 3606000. These values are in good agreement with recent modeling by Herbst & Woon and confirm that the reaction of HOC+ with H2 indeed has a substantial barrier at low (T < 50 K) temperatures. The widespread abundance of HOC+ additionally suggests that there is not a strong preference for synthesis of this ion in photon-dominated regions, although there may be a small enhancement toward such gas. Finally, confirmation of interstellar HOC+ has been accomplished through observations of weak emission (TR ≲, 50 mK) at 179 GHz, proving that measurements near the atmospheric water line at 183 GHz are not as difficult as previously thought. © 1997. The American Astronomical Society. All rights reserved.
• Li, B. -., & Ziurys, L. M. (1997). Laboratory detection and submillimeter spectrum of the NaS radical (X²II_i). Astrophysical Journal Letters, 488(2 PART II), L137-L140.
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  Abstract: The sodium sulfide radical NaS has been observed in the laboratory for the first time using millimeter/ submillimeter direct absorption spectroscopy. Twelve rotational transitions originating in both the Ω = 1/2 and 3/2 sublevels of this species in its X2IIi ground state were recorded in the frequency range 200-400 GHz. Splittings arising from lambda-doubling interactions were resolved in both spin-orbit components and were particularly large (∼2.9 GHz) in the Ω = 1/2 substate. The data were analyzed using a 2II Hamiltonian, and rotational, spin-orbit, and lambda-doubling parameters were determined. NaS may be detectable in the late-type star IRC + 10216, given the observation of CS, SiS, NaCl, and NaCN in this object. © 1997. The American Astronomical Society. All rights reserved.
• Li, B. -., Xin, J., & Ziurys, L. M. (1997). The pure rotational spectrum of NaCH₃ ( X̃¹A₁ ). Chemical Physics Letters, 280(5-6), 513-519.
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  Abstract: The pure rotational spectrum of NaCH3 and NaCD3 in their X̃1A1 states has been recorded using millimeter/sub-mm direct absorption techniques in the 300-510 GHz range. This work is the first gas-phase detection of sodium monomethyl, which was created by the reaction of sodium vapor with tetramethyl tin. Ten rotational transitions were measured for NaCH3 for the K=0 through K=5 components and, in select cases, up to K=10, and four transitions (K=0-7) for NaCD3. Rotational constants have been accurately determined for both isotopomers, suggesting a sodium-carbon bond length of 2.30 Å and an H-C-H bond angle of 107.3°.
• Li, B. Z., & Ziurys, L. M. (1997). Laboratory detection and submillimeter spectrum of NaCCH (X̄¹∑). Astrophysical Journal Letters, 482(2 PART II), L215-L217.
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  Abstract: Sodium monoacetylide has been observed in the laboratory for the first time using millimeter/submillimeter direct absorption techniques. The species was produced by the reaction of sodium vapor and acetylene under DC discharge conditions. Nineteen rotational transitions of NaCCH in its X 1∑ ground state and 14 lines of the deuterium isotopomer NaCCD were recorded in the range 270-510 GHz. From these data, highly accurate rotational constants were determined. The detection of NaCN and NaCl in the envelope of the evolved carbon star IRC +10216 suggests that other sodium-bearing species may be present in this object. © 1997. The American Astronomical Society. All rights reserved.
• Robinson, J. S., Apponi, A. J., & Ziurys, L. M. (1997). The millimeter-wave spectrum of A1NC: Chemical trends in metal isocyanide molecules. Chemical Physics Letters, 278(1-3), 1-8.
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  Abstract: The millimeter-wave spectrum of A1NC (X 1Σ+) has been recorded using direct absorption techniques in the range 131-536 GHz, including data for several quanta of the bending vibration and the 13C isotopomer. The species was created by the reaction of aluminum vapor and trimethylsilyl cyanide. Twenty rotational transitions were recorded for the main isotopomer and nine for A1N13C, as well as lines for the (0110), (0200), and (0220) states. Rotational and l-type doubling constants have been determined for this species, as well as bond lengths. These measurements indicate that A1NC is a linear and fairly rigid molecule, as well as being the favored isomer, in agreement with theory. © 1997 Elsevier Science B.V.
• Allen, M. D., & Ziurys, L. M. (1996). The millimeter-wave spectrum and rest frequencies of FeF (X⁶Δ_i). Astrophysical Journal Letters, 470(2 PART I), 1237-1242.
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  Abstract: The pure rotational spectrum of the FeF radical (X6Δi) has been measured in the laboratory using millimeter/submillimeter direct absorption techniques. FeF was created by the reaction of iron vapor, produced in a high-temperature Broida-type oven, and F2. Eleven rotational transitions in the frequency range 121-374 GHz were recorded in all six spin-orbit components. Lambda-type doubling was resolved in the Ω2 = 3/2, 1/2, and -1/2 sublevels, and hyperfine structure, arising from the fluorine nuclear spin, was observed in all spin-orbit ladders. The data were successfully analyzed using a 6Δ Hamiltonian and rotational, spin-orbit, spin-spin, lambda-doubling, and hyperfine parameters were determined. The observation of A1F in the circumstellar shell of IRC+10216 suggests that other fluoride molecules such as FeF may be present in this object. © 1996. The American Astronomical Society. All rights reserved.
• Allen, M. D., Pesch, T. C., & Ziurys, L. M. (1996). The pure rotational spectrum of FeC (X³Δ_i). Astrophysical Journal Letters, 472(1 PART II), L57-L60.
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  Abstract: The pure rotational spectrum of the FeC radical (X 3Δi) has been measured in the laboratory for the first time using millimeter/submillimeter direct absorption techniques. FeC was created by the reaction of iron vapor, produced in a high-temperature Broida-type oven, and methane gas under DC discharge conditions. Six rotational transitions each were recorded for the two lower spin-orbit ladders of this molecule in the frequency range 240-484 GHz, as well as six transitions for the Ω = 3 ladder of the iron isotopomer 54FeC. The data were analyzed using a 3Δ Hamiltonian, and rotational and certain spin-orbit parameters were determined. The observation of SiC in the circumstellar shell of IRC +10216 suggests that metal carbides such as FeC may be present as well. © 1996. The American Astronomical Society. All rights reserved.
• Allen, M. D., Ziurys, L. M., & Brown, J. M. (1996). The millimeter-wave spectrum of FeO in its X⁵Δ_i state (v = 0): A study of all five spin components. Chemical Physics Letters, 257(1-2), 130-136.
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  Abstract: New millimeter/sub-millimeter pure rotational spectroscopy has been carried out for the FeO radical (X5Δi). The molecule was produced by the reaction of N2O with iron vapor, generated using a Broida-type oven. In addition to verifying previous measurements on FeO in the lower spin-orbit components, transitions originating in the Ω = 0 and 1 ladders have been recorded, for which lambda-type doubling was resolved. Spectra of the 54FeO isotopomer were also measured. The data set was analyzed successfully with a 5Δ Hamiltonian, demonstrating that highly perturbed, complicated electronic ground states can be modeled with effective rotational parameters.
• Anderson, M. A., Robinson, J. S., & Ziurys, L. M. (1996). The pure rotational spectrum of the ground vibrational state of SrCH₃(Χ̃ ²Α₁). Chemical Physics Letters, 257(5-6), 471-480.
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  Abstract: The pure rotational spectrum of the SrCH3 radical (Χ̃ 2Α1) has been recorded using millimeter/sub-mm direct absorption techniques in the range 162-371 GHz. These data are the first high resolution measurements of this symmetric top species. The Κ = 0, 1, 2, and 3 components in each of seventeen rotational transitions of SrCH3 were observed, including fine structure splittings. Rotational and spin-rotation parameters have been obtained for SrCH3, and its structural and electronic properties are compared with those of other strontium radicals and metal monomethyl compounds. Substantial spin-orbit interactions appear to influence the fine structure splittings in these metal monomethyl species.
• Ohishi, M., Ishikawa, S. I., Amano, T., Oka, H., Irvine, W. M., Dickens, J. E., Ziurys, L. M., & Apponi, A. J. (1996). Detection of a new interstellar molecular ion, H2COH+ (protonated formaldehyde).. The Astrophysical journal, 471(1), L61-64.
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  PMID: 11541244;Abstract: A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 1(1,0)-1(0,1) transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC + 10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 10(12)-10(14) cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10(-11) to 10-(9), and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3OH may play an important role in the formation of H2COH+.
• Ohishi, M., Ishikawa, S., Amano, T., Oka, H., Irvine, W. M., Dickens, J. E., Ziurys, L. M., & Apponi, A. J. (1996). Detection of a new interstellar molecular ion, H₂COH⁺ (protonated formaldehyde). Astrophysical Journal Letters, 471(1 PART II), L61-L64.
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  Abstract: A new interstellar molecular ion, H2COH+ (protonated formaldehyde), has been detected toward Sgr B2, Orion KL, W51, and possibly in NGC 7538 and DR21(OH). Six transitions were detected in Sgr B2(M). The 11,0-10,1 transition was detected in all sources listed above. Searches were also made toward the cold, dark clouds TMC-1 and L134N, Orion (3N, 1E), and a red giant, IRC +10216, without success. The excitation temperatures of H2COH+ are calculated to be 60-110 K, and the column densities are on the order of 1012-1014 cm-2 in Sgr B2, Orion KL, and W51. The fractional abundance of H2COH+ is on the order of 10-11 to 10-9, and the ratio of H2COH+ to H2CO is in the range 0.001-0.5 in these objects. The values in Orion KL seem to be consistent with the "early time" values of recent model calculations by Lee, Bettens, & Herbst, but they appear to be higher than the model values in Sgr B2 and W51 even if we take the large uncertainties of column densities of H2CO into account. We suggest production routes starting from CH3 OH may play an important role in the formation of H2COH+. © 1996. The American Astronomical Society. All rights reserved.
• Robinson, J. S., & Ziurys, L. M. (1996). The millimeter and submillimeter spectrum of AlCH₃ (X̃¹a₁). Astrophysical Journal Letters, 472(2 PART II), L131-L134.
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  Abstract: The pure rotational spectrum of AlCH3 has been recorded using millimeter/submillimeter direct absorption techniques. This is the first time this species has been observed in the laboratory by any spectroscopic method. AlCH3 was created in a d.c. discharge by the reaction of aluminum vapor and dimethyl mercury. The K = 0, 1, 2, and 3 components in fourteen rotational transitions of this symmetric top molecule were measured in the frequency range 188-517 GHz and several lines recorded for K = 4, 5 and 6 ladders as well. From these data, rotational parameters have been accurately determined. This study confirms the structure predicted for AlCH3 from theoretical calculations, as well as provides precise rest frequencies. Aluminum-bearing molecules have been observed in the late-type carbon star IRC +10216, which also has a large abundance of CH4. Hence, AlCH3 may be detectable in this object and perhaps in other sources. © 1996. The American Astronomical Society. All rights reserved.
• Womack, M., Apponi, A. J., & Ziurys, L. M. (1996). A search for interstellar ch₃d: limits to the methane abundance in orion-kl. Astrophysical Journal Letters, 461(2 PART I), 897-901.
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  Abstract: A search has been performed for interstellar CH3D via its JK = 10-00 transition at 232 GHz and its JK = 20-10 and JK = 21-11 lines at 465 GHz using the NRAO 12 m and CSO 10 m telescopes toward Orion-KL. This search was done in conjunction with laboratory measurements of all three transitions of CH3D using millimeter/submillimeter direct absorption spectroscopy. The molecule was not detected down to a 3 σ level of TA< 0.05 K for the JK = 21-11 line toward Orion, which indicates an upper limit to the CH3D column density of N < 6 × 1018 cm-2 in the hot core region and a fractional abundance (with respect to H2) of
• Ziurys, L. M., Fletcher, D. A., Anderson, M. A., & Barclay Jr., W. L. (1996). Rest frequencies for alkaline earth hydroxide radicals (X²Σ⁺). Astrophysical Journal, Supplement Series, 102(2), 425-434.
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  Abstract: Rest frequencies for the pure rotational transitions of the alkaline earth hydroxide radicals MgOH, CaOH, SrOH, and BaOH are presented. These data were obtained using millimeter/submillimeter direct absorption spectroscopy in the range 100-400 GHz. The hydroxide molecules, which all have 2Σ+ ground electronic states, were created by the reaction of hydrogen peroxide and metal vapor, produced in a Broida-type oven. Transitions arising in the ground (000) state as well as excited vibrational modes (0110), (0200), (0220), and (100), were recorded. Fine-structure splittings were resolved in every transition. The data were analyzed using a 2Σ Hamiltonian, and rotational, fine-structure, and l-type doubling constants were determined for the radicals. These measurements will enable the identification of the alkaline earth hydroxide species in the interstellar medium.
• Anderson, M. A., & Ziurys, L. M. (1995). The millimeter/submillimeter rotational spectrum of CaCCH(X²Σ⁺). Astrophysical Journal Letters, 444(1 PART 2), L57-L60.
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  Abstract: The pure rotational spectrum of the CaCCH radical (X2Σ+) has been measured in the laboratory using millimeter/submillimeter direct absorption spectroscopy. The species was created in a d.c. discharge by the reaction of calcium vapor and acetylene. Twenty-two rotational transitions of this molecule were recorded in the frequency range 230-380 GHz to an accuracy of ± 150 kHz. Spin-rotation splittings, but no proton hyperfine structure, were observed for CaCCH. The data were analyzed using a 2Σ Hamiltonian, and rotational and fine structure constants were determined. These measurements have resulted in accurate rest frequencies for CaCCH to be used for astronomical searches. A calcium-bearing molecule has yet to be observed in interstellar or circumstellar gas.
• Bunker, P. R., Kolbuszewski, M., Jensen, P., Brumm, m., Anderson, M. A., Barclay Jr., W. L., Ziurys, L. M., Ni, Y., & Harris, D. O. (1995). New rovibrational data for MgOH and MgOD and the internuclear potential function of the ground electronic state. Chemical Physics Letters, 239(4-6), 217-222.
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  Abstract: Using millimeter wave absorption spectroscopy we have recorded pure rotation spectra of MgOH in its ground vibrational state and in six excited vibrational states. We have also determined a large number of bending vibrational energies, and the MgO stretching frequency, using dispersed fluorescence studies of both MgOH and MgOD. By a weighted least-squares optimized fitting to this data, using the vibrational approach MORBID (Morse oscillator rigid bender for internal dynamics), we have derived the full ground state potential surface in an analytical form. The equilibrium structure is determined to be linear but with a flat predominantly quartic bending potential. © 1995.
• Fletcher, D. A., Anderson, M. A., Barclay Jr., W. L., & Ziurys, L. M. (1995). Millimeter-wave spectroscopy of vibrationally excited ground state alkaline-earth hydroxide radicals (X ²Σ⁺). The Journal of Chemical Physics, 102(11), 4334-4339.
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  Abstract: Pure rotational spectra of the alkaline-earth monohydroxides have been recorded for vibrationally excited states (0 1 0), (0 2 0), (0 3 0), and (1 0 0) of the ground electronic state (X 2Σ+) using millimeter-wave absorption spectroscopy. The radicals MgOH, CaOH, SrOH, and BaOH were studied. The data for CaOH, SrOH, and BaOH were analyzed with a linear 2Σ+ model, but with the addition of two terms to account for contamination of the υ2 = 1 2Π and υ2 = 2 2Δ vibronic levels with 2Π and 2Δ electronic states. The data for MgOH, however, did not fit well to this linear model and is additional evidence that this species is quasilinear. © 1995 American Institute of Physics.
• Nuccio, B. P., Apponi, A. J., & Ziurys, L. M. (1995). Millimeter-wave rotational spectroscopy of MgOD and CaOD (X ²Σ⁺). The Journal of Chemical Physics, 103(21), 9193-9199.
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  Abstract: Pure rotational spectra of CaOD and MgOD have been recorded in the range 200-390 GHz using millimeter/sub-mm direct absorption spectroscopy. Transitions arising from the (000), (010), (020), and (100) modes have been measured for the 2Σ+ ground electronic states of these free radicals. The data were analyzed successfully using a linear 2Σ+ model for CaOD; for MgOD, only the (000) and (010) states could be fit with this Hamiltonian. Moreover, the (010) data required the addition of a substantial pΠ term to account for contamination of excited 2Π electronic states. For both species, the α2 vibration-rotation term was found to be negative, in contrast to MgOH and CaOH, suggesting a less anharmonic contribution to the bending potential in CaOD and MgOD. These measurements also indicate a shorter O-H bond in MgOH than the other alkaline earth hydroxide radicals, which likely results because this species is quasilinear. © 1995 American Institute of Physics.
• Nuccio, B. P., Apponi, A. J., & Ziurys, L. M. (1995). The millimeter-wave spectrum of SrCCH(X²Σ⁺): chemical trends in metal monoacetylide species. Chemical Physics Letters, 247(3), 283-288.
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  Abstract: The pure rotational spectrum of the SrCCH radical (X2Σ+) has been recorded using millimeter/sub-mm direct absorption techniques. SrCCH was synthesized in a dc discharge by the reaction of strontium vapor, produced in a Broida-type oven, and acetylene. Seventeen rotational transitions of this molecule were recorded in the range 248-370 GHz and fine structure splittings resolved. Rotational and spin-rotation parameters were determined using a 2Σ Hamiltonian. SrCCH appears to be linear with an ionic structure, as previously suggested. Comparison of structural parameters with MgCCH and CaCCH suggest subtle differences in the bonding of these monoacetylide species. © 1995.
• Sage, L. J., & Ziurys, L. M. (1995). Toward extragalactic chemistry: Detections of N₂H⁺ and SiO in nearby galaxies. Astrophysical Journal Letters, 447(2), 625-629.
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  Abstract: Observations of N2H+ and SiO in a sample of nine nearby galaxies have been carried out. N2H+ was newly detected in two and confirmed in five. Four galaxies were newly detected in SiO, and emission from one other was confirmed. In addition, two galaxies showed evidence of HCO emission, a possible new extragalactic molecule. With the exception of M82, the abundance of N2H+ is fairly uniform in these sources, with [N2H+]/[H2] ∼ 6 × 10-11, close to concentrations typically found in Galactic clouds. The SiO abundances of 1-4 × 10-11, on the other hand, seem more sensitive to the star formation rate, possibly reflecting the differing fractions of molecular gas that are currently forming massive stars. However, the abundance of this species seems low in M82, a starburst galaxy. In addition, the behavior of the molecules, when compared to CS - which traces dense gas without regard to temperature - is not what was naively expected. These observations suggest that while extragalactic chemistry may be similar to that in the Milky Way, there are substantial differences which have yet to be analyzed.
• Ziurys, L. M., & Apponi, A. J. (1995). Confirmation of interstellar HOC⁺: Reevaluating the [HCO⁺]/[HOC⁺] abundance ratio. Astrophysical Journal Letters, 455(1 PART 2), L73-L76.
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  Abstract: The identification of interstellar HOC+ has been confirmed through new observations of this species at 3, 2, and 1.2 mm using the NRAO 12 m telescope. Toward Sgr B2 (OH), the J = 2 → 1 and J = 3 → 2 lines of this ion at 179 and 268 GHz were detected for the first time. In addition, the J = 1 → 0 line of HOC+ at 89 GHz was observed toward several new sources, including Orion-KL. In conjunction with past observations of the J = 1 → 0 transition toward Sgr B2 (OH), these data clearly establish the presence of this species in the interstellar medium. The column density toward Sgr B2 (OH) is estimated to be Ntot ∼ 3 × 1012 cm-2, which corresponds to a fractional abundance relative to H2 of f ∼ 10-12. Measurements of HCO+ were also carried out toward Sgr B2 (OH), resulting in an abundance ratio of [HCO+]/[HOC+] ∼ 140-360 at gas densities of n(H2) > 105 cm-3. This ratio contradicts past predictions of ion-molecule models by several orders of magnitude and suggests that the reaction HOC+ + H2 → HCO+ + H2 is not as fast as previously thought.
• Ziurys, L. M., Apponi, A. J., Guélin, M., & Cernicharo, J. (1995). Detection of MgCN in IRC +10216: A new metal-bearing free radical. Astrophysical Journal Letters, 445(1 PART 2), L47-L50.
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  Abstract: A new metal-containing molecule, MgCN, has been detected toward the late-type star IRC +10216, using the NRAO 12 m and IRAM 30 m telescopes. The N = 11 → 10, 10 → 9, and 9 → 8 transitions of this species, which has a 2Σ+ ground state, have been observed in the outer envelope of this object at 3 mm. For the N = 11 → 10 transitions, the two spin-rotation components are clearly resolved and conclusively identify this new radical. These measurements imply a column density for MgCN of Ntot ∼ 1012 cm-2 in the outer shell, which corresponds to a fractional abundance of f ∼ 7 ×10-10. This molecule, the metastable isomer of MgNC, is the third metal-bearing species thus far identified in the outer shell of IRC +10216, and its detection implies a ratio of MgNC/MgCN ∼ 22/1. MgCN may be formed through a reaction scheme involving magnesium and HNC or CN, both prominent outer shell molecules, or through synthesis on grains.
• Anderson, M. A., & Ziurys, L. M. (1994). Metal hyperfine structure in magnesium chloride. The millimeter-wave spectrum of ²⁵MgCl and ²⁶MgCl. Chemical Physics Letters, 224(3-4), 381-390.
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  Abstract: Rotational spectra of the magnesium and chlorine isotopomers of MgCl (X 2ε{lunate}+) have been measured in the frequency range 260-380 GHz using direct absorption techniques. The species studied (25Mg35Ml, 25Mg37Cl, and 26Mg37Cl) were created in a dc glow discharge by the reaction of magnesium vapor with CCl4. Several rotational transitions were recorded for each isotopomer, and fine structure, as well as hyperfine splittings due to the 25Mg nucleus, were observed. Rotational, spin-rotation and hyperfine constants were determined for these radicals. The average value of the Fermi contact terms was bF(25Mg) = -317.8 (4.9) MHz, indicating a large electron density at the magnesium nucleus. © 1994.
• Anderson, M. A., & Ziurys, L. M. (1994). The millimeter-wave spectrum of²⁵MgNC and ²⁶MgNC: bonding in magnesium isocyanides. Chemical Physics Letters, 231(2-3), 164-170.
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  Abstract: Rotational spectra of the 25Mg and 26Mg isotopomers of MgNC have been recorded in the frequency range 298-386 GHz using millimeter/sub-millimeter direct absorption spectroscopy. The species were created in their natural isotopic ratios in a dc discharge of cyanogen gas and magnesium vapor. Rotational and fine structure parameters were determined for these radicals, as well as magnesium 25 hyperfine constants for 25MgNC. For this isotopomer, bF ≈ -298(16), indicating a large electron density at the nucleus and an ionic type Mg+NC- structure, as expected for a linear configuration. R0 bond lengths were also derived, which are in good agreement with theoretical calculations. © 1994.
• Anderson, M. A., Allen, M. D., & Ziurys, L. M. (1994). Millimeter and submillimeter rest frequencies for the MgF radical. Astrophysical Journal Letters, 425(1 PART 2), L53-L57.
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  Abstract: The pure rotational spectrum of the MgF radical in its ground X 2Σ++ electronic state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Rotational transitions arising from the υ = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, 24MgF, have been recorded, as well as those arising from the υ = 0 state of the 25Mg and 26Mg isotopomers. Rotational and fine-structure constants have been determined for these molecules, as well as hyperfine parameters for both the 19F (I = 1/2) and 25Mg (I = 5/2) nuclei. The rest frequencies presented here for MgF have an estimated accuracy of ±200 kHz, and will enable astronomical searches to be carried out for this fluoride radical. Magnesium fluoride may be present in the late-type carbon star IRC + 10216, where AlF appears to be abundant.
• Anderson, M. A., Allen, M. D., & Ziurys, L. M. (1994). Millimeter-wave spectroscopy of MgF: Structure and bonding in alkaline-earth monofluoride radicals. The Journal of Chemical Physics, 100(2), 824-830.
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  Abstract: The pure rotational spectrum of the MgF radical in its ground electronic state (X2∑+) has been recorded using millimeter/submillimeter direct absorption techniques. Transitions arising from the v = 0, 1, 2, and 3 vibrational modes of the main magnesium isotopic species, 24MgF, have been observed. In addition, spectra of the isotopomers 26MgF and 25MgF in the natural abundances of magnesium have been detected. Rotational and fine structure constants have been determined for these species, as well as hyperfine parameters for the fluorine nucleus (I = 1/2). For 25MgF, the hyperfine structure was also resolved arising from the magnesium nucleus, which has I=5/2, yielding the 25Mg hyperfine and quadrupole constants. Comparison of these hyperfine parameters with those of the heavier alkaline-earth monofluorides and the free 25Mg+ atom suggests that there is an increase in covalent bonding in MgF vs its heavier fluoride counterparts. This behavior is also apparent in the hybridization of the wave function of the unpaired electron in MgF, which appears to consist of almost equal s and p character. © 1994 American Institute of Physics.
• Anderson, M. A., Allen, M. D., & Ziurys, L. M. (1994). The millimeter-wave spectrum of the CaF radical (X ²∑⁺). Astrophysical Journal Letters, 424(1), 503-506.
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  Abstract: The pure rotational spectrum of the CaF radical has been measured in the laboratory using millimeter/sub-mm direct absorption specstroscopy. Fourteen rotational transitions have been detected originating in the v = 0 mode of the species. Rotational lines of the vibrationally excited v = 1, 2, and 3 states have also been observed. Spin-rotation splittings, as well as hyperfine interactions arising from the nuclear spin of the fluorine atom, were resolved in the CaF spectra. Rotational, fine-structure, and in some cases, hyperfine parameters were determined for the various vibrational modes of the molecule from a nonlinear least-squares fit to the data, using a 2∑ Hamiltonian, and are in agreement with past measurements. The newly measured rest frequencies for CaF, which are accurate to at least ± 100 kHz, will enable astronomical searches to be conducted for the molecule in interstellar and circumstellar gas. Given the recent detection of AlF in IRC + 10216, metal fluoride species may be more abundant than previously thought.
• Tauber, J. A., Snell, R. L., Dickman, R. L., & Ziurys, L. M. (1994). High-resolution images of shocked molecular clumps in the supernova remnant IC 443. Astrophysical Journal Letters, 421(2), 570-580.
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  Abstract: We present high angular resolution interferometric observations of HCO+ J = 1 → 0 line emission from two molecular clumps which are being shocked by the blast wave from the supernova which formed the remnant IC 443. Our observations show that a range of gas densities exist within these clumps; this fact may explain the mixture of shock velocities inferred from other observations. Previous studies have shown evidence that molecular material is being accelerated by the blast wave in a systematic fashion around one of the clumps that we study. We show that this phenomenon also occurs at the small spatial scales that we observe. In addition, we present evidence that suggests that the velocity field may correspond to ablation from or a bow shock around the denser cores present within the clumps.
• Ziurys, L. M., Apponi, A. J., & Phillips, T. G. (1994). Exotic fluoride molecules in IRC +10216: Confirmation of AlF and searches for MgF and CaF. Astrophysical Journal Letters, 433(2), 729-732.
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  Abstract: Three new rotational transitions of aluminum fluoride (AlF) at 0.8 and 1.2 mm have been observed. The J = 10 → 9, J = 8 → 7, and J = 7 → 6 lines of AlF at 230, 263, and 329 GHz, respectively, were seen toward IRC +10216 using the Caltech Submillimeter Observatory (CSO). Combined with the earlier data obtained for this species at IRAM at 2 and 3 mm, these measurements confirm the presence of the metal halide in this carbon-rich circumstellar shell. Analysis of the CSO and IRAM data suggests that AlF arises from a source with a diameter of θs ∼ 5″-10″ and hence is present chiefly in the inner envelope of IRC +10216. In this region, the molecule has a column density of (0.3-1.1) × 1015 cm-2, which indicates a fractional abundance of at least ∼10-9, relative to H2. Searches for the metal fluoride species CaF and MgF have also been conducted toward IRC +10216, but with negative results. The column density upper limits for MgF and CaF are Ntot < (1-4) × 1014 cm-2. Relative abundances of these metal fluoride molecules can be understood in terms of chemical thermodynamic equilibrium. The presence of AlF in IRC +10216 also indicates that large quantities of fluorine must be present in the inner stellar envelope, suggesting that this element may be produced not primarily in explosive nucleosynthesis but rather in helium shell flashes, as indicated also by HF spectroscopy of red giant stars.
• Ziurys, L. M., Apponi, A. J., Hollis, J. M., & Snyder, L. E. (1994). Detection of interstellar N₂O: A new molecule containing an N-O bond. Astrophysical Journal Letters, 436(2 PART 2), L181-L184.
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  Abstract: A new interstellar molecule, N2O, known as nitrous oxide or "laughing gas," has been detected using the NRAO 12 m telescope. The J = 3 → 2, 4 → 3, 5 → 4, and 6 → 5 rotational transitions of this species at 75, 100, 125, and 150 GHz, respectively, were observed toward Sgr B2(M). The column density derived for N2O in this source is Ntot ∼ 1015 cm-2, which corresponds to a fractional abundance of ∼ 10-9, relative to H2. This value implies abundance ratios of N2O/NO ∼ 0.1 and N2O/HNO ∼ 3 in the Galactic center. Such ratios are in excellent agreement with predictions of ion-molecule models of interstellar chemistry using early-time calculations and primarily neutral-neutral reactions. N2O is the third interstellar molecule detected thus far containing an N-O bond. Such bonds cannot be so rare as previously thought.
• Ziurys, L. M., Barclay Jr., W. L., Anderson, M. A., Fletcher, D. A., & Lamb, J. W. (1994). Millimeter/submillimeter spectrometer for high resolution studies of transient molecules. Review of Scientific Instruments, 65(5), 1517-1522.
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  Abstract: A millimeter/sub-mm spectrometer was used to study metal bearing free radicals. Gun oscillators were utilized as the tunable source of radiation from 65-140 6Hz. Higher source frequencies were provided by Schottky diode multipliers. Gaussian beam optics were utilized in the design of gas and cell optics. Scalar feedhoms and PTFe lenses propagated the source signal. The gas cell was a cylindrical tube .5 m is length with detachable even. The spectrometer operated in the frequency range of 65-550 GHz. The instrumental resolution was 200-1000 kHz. It had an absorption sensitivity of a few ppm. Pure rotational spectra of metal hydroxide, fluoride and metal hydride were measured. Measurement was also done on multiple rotational transitions. The frequencies of 23 rotational transitions of BaOH were measured over the range of 77-376 GHz. 19 transitions of SrOH were observed in the region 89-370 GHz. Linewidths observed for radicals and closed shell spaces ranged from 200-900 kHz. Fine and hyperfine structures were also resolved. Rare isotopomers were also detected. They included BaOH with the 137Ba and 136Ba nuclei. These results demonstrated the versatility and sensitivity of the instrument.
• Ziurys, L. M., Hollis, J. M., & Snyder, L. E. (1994). New detections of interstellar HNO at 2 and 1.2 millimeters: More N-O bonds. Astrophysical Journal Letters, 430(2), 706-712.
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  Abstract: The 202-101 and 303-202 transitions of HNO at 163 and 244 GHz have been detected toward several molecular clouds. In conjunction with previous measurements of the 101-000 line at 81 GHz, these observations secure the identification of interstellar HNO. The 202-101 transition of this species has been detected toward NGC 2024, Sgr B2 (NW), W51M, and DR 21 (OH), while the 303-202 line at 1.2 mm was observed only in NGC 2024. Typical column densities of HNO observed toward these sources are Ntot ∼ 1012-1014 cm-2, corresponding to fractional abundances of fHNO ∼ 10-11 to 10-10. These values imply NO/HNO ratios of ∼ 100-800. Both the HNO fractional abundances and NO/HNO ratios are in reasonable agreement with predictions of ion-molecule-type models of interstellar chemistry, provided early-time calculations are used. Such behavior contrasts with that of other nitrogen compounds, whose observed abundances are best duplicated by steady-state calculations. The chemistries of HNO and NO are thus likely to be related. These observations also suggest that interstellar N-O bonds may be more common than previously thought.
• Anderson, M. A., & Ziurys, L. M. (1993). Laboratory detection and millimeter spectrum of the MgCCH radical. Astrophysical Journal Letters, 439(1 PART 2), L25-L28.
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  Abstract: The pure rotational spectrum of the magnesium monoacetylide radical, MgCCH, has been recorded in the laboratory using millimeter/sub-mm direct absorption spectroscopy. These measurements constitute the first time this molecule has been observed in the laboratory by any spectroscopic method. Seventeen rotational transitions were observed in the frequency range 210-370 GHz for MgCCH, which appears to be a linear molecule with a 2Σ ground electronic state. Rotational and fine structure constants were determined for this radical from a nonlinear least squares fit to the data. The rotational rest frequencies measured here will enable astronomical observations to be carried out for MgCCH towards IRC +10216, where the magnesium compounds MgCN and MgNC, as well as many acetylide species, are present.
• Anderson, M. A., & Ziurys, L. M. (1993). The millimeter/submillimeter spectrum and rotational rest frequencies of MgCH₃(X̃ ²A₁). Astrophysical Journal Letters, 452(2 PART 2), L157-L160.
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  Abstract: The pure rotational spectrum of the free radical MgCH3(X̃ 2A1) has been measured in the laboratory for the first time using millimeter/submillimeter direct absorption spectroscopy. The molecule was made in a DC discharge by the reaction of magnesium vapor and dimethyl mercury. Ten rotational transitions of this species were observed in the range 176-374 GHz. MgCH3 is a symmetric top molecule with net spin angular momentum. Consequently, both K structure and spin-rotation interactions were observed in every rotational transition. The data were analyzed with a 2A1 Hamiltonian and rotational, centrifugal distortion, and tine-structure parameters were accurately determined. These measurements will now enable a search for this radical in interstellar and 1 circumstellar sources to be conducted using millimeter/submillimeter telescopes.
• Anderson, M. A., Allen, M. D., Barcaly Jr., W. L., & Ziurys, L. M. (1993). The millimeter and sub-millimeter spectrum of the BaOH radical. Chemical Physics Letters, 205(4-5), 415-422.
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  Abstract: The pure rotational spectrum of the X2Σ+ ground electronic states of the BaOH and BaOD radicals has been observed using millimeter/sub-millimeter direct absorption spectroscopy. The lesser abundant isotopically substituted species, 136BaOH and 137BaOH, have been detected as well. The radicals were created by reacting barium metal vapor, produced in a Broida-type oven, with either H2O2 or D2O2. The rotational and spin-rotation constants were determined for the molecules from a nonlinear leastsquares fit to the data, using a 2Σ Hamiltonian. Hyperfine constants were also derived for 137BaOH, the one species where hyperfine structure was resolved. These measurements confirm a linear structure for BaOh. © 1993.
• Apponi, A. J., Barclay Jr., W. L., & Ziurys, L. M. (1993). The millimeter-wave spectrum of AlOH. Astrophysical Journal Letters, 414(2 PART 2), L129-L132.
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  Abstract: The pure rotational spectrum of the AlOH and AlOD molecules in their X1Σ+ (v = 0) ground electric states has been measured in the laboratory using direct absorption millimeter/sub-millimeter spectroscopy. The species were produced by the reaction of aluminum vapor, created in a Broida-type oven, with hydrogen peroxide or D2O2. Eight rotational transitions of AlOH and five transitions for AlOD were measured in the frequency range of 157-378 GHz to an accuracy better than ±75 kHz. Electric quadrupole interactions, arising from the aluminum nuclear spin of 5/2, were observed in the J = 4 → 5 and the J = 5 → 6 transitions of AlOH. The rotational constants of these molecules have been determined from a nonlinear least-squares fit to the data. The electric quadrupole coupling constant, eqQ, has been measured as well, and was found to have a value of -42.4 ± 4.3 MHz. The spectra are consistent with quasi-linear ground states for AlOH and AlOD, as predicted by theory. AlOH is of astrophysical interest because of the relatively high cosmic abundance of aluminum.
• Barclay Jr., W. L., Anderson, M. A., & Ziurys, L. M. (1993). The millimeter-wave spectrum of CaH (X²Σ⁺). Astrophysical Journal Letters, 408(1 PART 2), L65-L67.
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  Abstract: The millimeter-wave spectrum of the CaH and CaD radicals (X2Σ+) has been observed in the laboratory via direct absorption spectroscopy. The species were generated by the reaction of calcium vapor, produced in a Broida-type oven, with hydrogen atoms created in a microwave discharge. The six hyperfine components of the N = 0 → 1 rotational transition of CaH near 254 GHz were resolved and their frequencies determined to an accuracy of ± 100 kHz. The main hyperfine lines originating in the N = 0 → 1, 1 → 2, and 2 → 3 rotational transitions of CaD were also detected. Spectroscopic constants were determined for both radicals from a nonlinear least squares fit to the data, using a 2Σ Hamiltonian. These measurements constitute the first laboratory observation of CaH at high spectral resolution, and are essential to the detection of this radical in interstellar space.
• Barclay Jr., W. L., Anderson, M. A., Ziurys, L. M., Kleiner, I., & Hougen, J. T. (1993). The laboratory spectrum of acetaedehyde at 1 millimeter (230-325 GHz). Astrophysical Journal, Supplement Series, 89(1), 221-226.
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  Abstract: The rotational spectrum of acetaldehyde (CH3CHO) in the frequency range 230-325 GHz has been measured in the laboratory using millimeter/submillimeter direct absorption spectroscopy. Over 250 transition frequencies are presented for this molecule for both A and E symmetry species in its ground (vt = 0) and first excited (vt = 1) torsional state, with experimental uncertainties of ±50 kHz. The data were fitted with a model involving an internal rotation potential function, which typically reproduces the measured frequencies to vobs - vcalc ≲ 50 kHz for both ground and vt = 1 state. These newly measured rest frequencies should aid in the identification of interstellar CH3CHO and in spectral line assignments for millimeter-band scans.
• Womack, M., Ziurys, L. M., & Sage, L. J. (1993). N₂H⁺ in the Orion ambient ridge: Cloud clumping versus rotation. Astrophysical Journal Letters, 406(1 PART 2), L29-L33.
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  Abstract: Spectra of the J = 1 → 0 transition of N2H+ have been obtained over a 2′ × 2′ area toward the Orion-KL/ IRc2 star-forming region with 26″ angular resolution using the IRAM 30 m telescope. The N2H+ emission, which exclusively traces the ridge gas, exhibits multiple radial velocities which appear to arise from the presence of at least four clouds of quiescent material. One cloud, ∼75″ in extent, lies to the N and NE of OrionKL, with a velocity of KLSR ∼ 9.5 km s-1. A second cloud, ∼60″ in extent, lies to the NW and W, with an average velocity of VLSR ∼ 7.2 km s-1. There appears to be such a sharp velocity discontinuity between these two clouds that both velocity components are present within a 15″ region centered near IRc2 and other infrared sources. A third region, ∼35″ in extent, with KLSR ∼ 8.1 km s-1, is seen ∼ 15″ S of IRc2 and is likely to arise from the compact ridge. A fourth velocity component of VLSR ∼ 6.4 km s-1 lies 15″-30″ SW of IRc2 and is attributed to Orion-S. The velocity structure of N2H+ , therefore, does not uniformly change across OMC-1 and, consequently, is inconsistent with the presence of large-scale (∼ 1′-2′) differential rotation of the extended ridge along the SW-NE axis about IRc2. The coincidence of the two larger clouds with star-forming activity in Orion-KL suggests that either the quiescent gas is being pushed apart or that the star formation may have been triggered by a cloud-cloud interaction.
• Ziurys, L. M., & McGonagle, D. (1993). The spectrum of Orion-KL at 2 millimeters (150-160 GHz).. The Astrophysical journal. Supplement series, 89(1), 155-187.
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  PMID: 11539839;Abstract: A spectral survey of Orion-KL has been carried out in the 2 mm atmospheric window in the frequency range 149.6-159.6 GHz, using the FCRAO 14 m telescope. Typical sensitivities achieved were T*A approximately 0.03-0.1 K, peak-to-peak. Over 180 spectral lines were detected, including approximately 45 unidentified features. The spectra were measured with a single-sideband receiver and, even at levels of T*A approximately 30 mK, are far from being confusion-limited. Fifteen known species were conclusively identified in Orion in this spectral region, with the largest numbers of lines arising from methyl formate, ethyl cyanide, methanol, and dimethyl ether. These species have beam-averaged column densities of N(tot) approximately 0.5-8 x 10(15) cm-2. Several other species have been tentatively observed, including acetaldehyde, C2S, and possibly EtOH. The large organic species, however, appear to arise from different regions. For example, CH3CCH and (CH3)2O come primarily from the extended ridge, while EtCN and VyCN exclusively arise in the hot core. This survey clearly demonstrates that the 2 mm window is rich in spectral lines. It also suggests there is much chemical selectivity in the formation of large organic interstellar molecules.
• Ziurys, L. M., & Mcgonagle, D. (1993). The spectrum of Orion-KL at 2 millimeters (150-160 GHz). Astrophysical Journal, Supplement Series, 89(1), 155-187.
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  Abstract: A spectral survey of Orion-KL has been carried out in the 2 mm atmospheric window in the frequency range 149.6-159.6 GHz, using the FCRAO 14 m telescope. Typical sensitivities achieved were TA* ∼ 0.03-0.1 K, peak-to-peak. Over 180 spectral lines were detected, including ∼45 unidentified features. The spectra were measured with a single-sideband receiver and, even at levels of TA* ∼ 30 mK, are far from being confusion-limited. Fifteen known species were conclusively identified in Orion in this spectral region, with the largest numbers of lines arising from methyl formate, ethyl cyanide, methanol, and dimethyl ether. These species have beam-averaged column densities of Ntot ∼ 0.5-8 × 1015 cm-2. Several other species have been tentatively observed, including acetaldehyde, C2S, and possibly EtOH. The large organic species, however, appear to arise from different regions. For example, CH3CCH and (CH3)2O come primarily from the extended ridge, while EtCN and VyCN exclusively arise in the hot core. This survey clearly demonstrates that the 2 mm window is rich in spectral lines. It also suggests there is much chemical selectivity in the formation of large organic interstellar molecules.
• Ziurys, L. M., Barclay Jr., W. L., & Anderson, M. A. (1993). The millimeter-wave spectrum of the MgH and MgD radicals. Astrophysical Journal Letters, 402(1 PART 2), L21-L24.
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  Abstract: The pure rotational spectrum of the MgH radical (X 2Σ+) in its ground state v = 0 and v = 1 vibrational modes has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. The rotational spectra of two isotopically substituted species, MgD and 26MgH, have been detected as well. These free radicals were produced by the reaction of magnesium, vaporized in a Broida-type oven, with hydrogen atoms generated in a microwave discharge. All six hyperfine components of the N = 0 → 1 transition of MgH in its v = 0 and v = 1 states have been directly measured to an accuracy of ± 50 kHz, and five components have been observed for 26MgH. The N = 0 → 1 and N = 1 → 2 transitions of MgD have also been detected. Rotational, fine structure, and hyperfine constants were determined for all species from a nonlinear least-squares fit to the data using a 2Σ Hamiltonian. Measurement of these frequencies for MgH should greatly aid in establishing its presence in interstellar space.
• Anderson, M. A., Barclay Jr., W. L., & Ziurys, L. M. (1992). The millimeter-wave spectrum of the SrOH and SrOD radicals. Chemical Physics Letters, 196(1-2), 166-172.
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  Abstract: The pure rotational spectra of the X 2Σ+ ground states of the SrOH and SrOD radicals have been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. The lesser abundant isotopically substituted species, 86SrOH, has been observed as well. The molecules were produced in a Broida-type oven by the reaction of Sr metal vapor with either H2O2 or D2O2. The rotational and spin-rotation constants were determined for the radicals from a nonlinear least-squares fit to the data using a 2Σ Hamiltonian. The millimeter-wave measurements support the picture that strontium hydroxide is linear in its ground electronic and vibrational state. © 1992.
• Barclay Jr., W. L., Anderson, M. A., & Ziurys, L. M. (1992). The millimeter-wave spectrum of the MgOH radical (X ²Σ⁺). Chemical Physics Letters, 196(3-4), 225-232.
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  Abstract: The pure rotational spectrum of the ground electronic state (X 2Σ+) of the MgOH radical has been observed using millimeter/sub-millimeter direct absorption spectroscopy, as well as that of MgOD, and the less abundant magnesium isotopically-substituted species 25MgOH and 26MgOH. The free radicals were created in a Broida-type oven by the reaction of metal vapor with hydrogen peroxide. The spin-rotation splitting was readily observed in these data; however, the hyperfine structure was only resolved for 25MgOH. The rotational and spin-rotation constants of the radicals have been determined from a non-linear least-squares fit using a 2Σ Hamiltonian. The 25Mg hyperfine constants are also estimated. © 1992.
• Dickman, R. L., Snell, R. L., Ziurys, L. M., & Huang, Y. (1992). Structure and kinematics of dense gas associated with the supernova remnant IC 443. Astrophysical Journal Letters, 400(1), 203-213.
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  Abstract: We present the results of systematic, high-resolution J = 1 → 0 CO and HCO+ mapping observations of IC 443 carried out with the FCRAO 14 m radio telescope. Five new clumps of perturbed molecular gas have been identified and their relationship to one another clarified. Together with three previously known perturbed regions, the clumps outline a roughly elliptical ring whose major axis is ∼9 pc across. There is a surprisingly systematic variation in the distribution of the high-velocity molecular gas associated with the clumps, which suggests that the clumps are distributed along the periphery of a tilted, expanding ring. The clumpiness of this ring may be a byproduct of the supernova blast wave's interaction with a more homogeneous confining structure or the clumps may have existed prior to the supernova event; in that case, their distribution may reflect the distribution of pre-existing dense cores in the ambient molecular gas, whose geometry has been revealed by the supernova stripping off overlying cloud material. High-resolution 1.3 mm CO maps of several clumps were also made. The most prominent clump in the supernova remnant possesses a velocity field with a strong systematic component, which we interpret as an indication that some of the high-velocity gas is ablated clump material accelerated at a shock interface between the clump and hot, outflowing gas within the supernova cavity. Assuming all the shocked CO emission in the SNR to be optically thin (an assumption which receives some support from 13CO observations made toward the center of one clump), we estimate the total mass of molecular gas perturbed by the SNR to be at least 500 M⊙. A similar estimate based on the HCO+ observations - an estimate which is unaffected by optical depth ambiguities and by the necessity of avoiding the spurious inclusion of quiescent foreground material in the mass estimate - yields a mass of ∼2000 M⊙. Together with the expansion velocity of the clumps, ∼25 km s-1, this leads to an expansion energy of ∼1049 ergs, ∼5%-10% of the total estimated blast wave-energy of the supernova event. The large value of the total clump mass and the lower limit to the [12C/13C] isotope ratio suggested by our observations establish that the shocked gas associated with IC 443 represents preexisting molecular cloud material now interacting with the supernova remnant.
• Womack, M., Wyckoff, S., & Ziurys, L. M. (1992). Observational constraints on solar nebula nitrogen chemistry: N₂/NH₃. Astrophysical Journal Letters, 401(2), 728-735.
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  Abstract: The abundance ratio N2/NH3 in comets and dense molecular clouds is predicted by chemical models to be critical diagnostic of physical and chemical conditions of the solar nebula. Observations of N+2 and NH2 in comet Halley and N2H+ and NH3 in nine Galactic star-forming regions are used to determine the average N2/NH3 abundance ratio in these objects. For comet Halley we find N2/NH3 ∼ 0.1, and for the quiescent gas in a sample of star-forming regions, N2/NH3 ∼ 170 ± 100. The cometary N2/NH3 ratio corrected for gasphase elemental nitrogen depletion in comet Halley indicates that the gas component in the comet-forming region of the solar nebula was N2/NH3 ∼4. Correcting the dense cloud value for depletion of ammonia onto grains yields a total (gas and grain) ratio, N2/NH3 ∼ 4. However, the depletion correction is highly uncertain because the N2 and NH3 abundances are not correlated with cloud temperature. We conclude that more realistic models which include condensation fractionation effects are required before the N2 and NH3 abundances in comet volatiles can be related to star-forming regions. We point out that the assumption N2 ≫ NH3 used as an initial condition in most models of solar nebula chemistry is consistent with the observations of dense molecular clouds but is not justified by observations of comet Halley.
• Womack, M., Ziurys, L. M., & Wyckoff, S. (1992). A survey of N₂H⁺ in dense clouds: Implications for interstellar nitrogen and ion-molecule chemistry. Astrophysical Journal Letters, 387(1), 417-429.
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  Abstract: Spectra of the N2H+ J = 1 → 0, J = 3 → 2 and 15NNH+ and N15NH+ J = 1 → 0 rotational transitions have been obtained toward a sample of star-forming and cold dark clouds in the Galaxy. Toward the starforming regions, line profiles are relatively narrow (typically 1-5 km s-1) and show no evidence of line wings, in contrast to the spectra of HCO+. The apparent absence of N2H+ in hot, shocked gas suggests that this ion may be a selective tracer of extended, quiescent material. Column densities of N2H+ were found to be Ntot ∼ 5 × 1012 cm-2 toward cold clouds and Ntot ∼ 1014 cm-2 toward warm clouds. These values correspond to fractional abundances, relative to H2, of f ∼ 4 × 10-10 toward both the warm and cold clouds. Such abundances agree well with predictions of quiescent cloud ion-molecule chemistry models, provided "steady state," not "early time" values are used. Thus, the abundance and distribution of N2H+ is well-explained by ion-molecule chemistry, provided it has reached steady state, as is found for interstellar NH3. In contrast, most abundances of simple interstellar molecules are better reproduced by models calculated for early times. The N2H+ results thus are further evidence that interstellar nitrogen chemistry is anomalous.
• Womack, M., Ziurys, L. M., & Wyckoff, S. (1992). Estimates of N₂ abundances in dense molecular clouds. Astrophysical Journal Letters, 393(1), 188-192.
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  Abstract: Interstellar N2 abundances toward 13 dark clouds and warm star-forming regions are derived from column densities measured for N2H+. The N2H+ abundances were determined from a millimeter-wavelength study of the molecule's J = 1 → 0 and J = 3 → 2 rotational transitions, as well as from observations of the 2NNH+ and N15NH+ isotopic spectra. Abundances of N2 were estimated from N2H+ assuming the chemistry had achieved steady state. Fractional abundances of N2 with respect to H2 are typically f ∼ 3 × 10-6 for eight warm clouds and f ∼ 6 × 10-6 for four cold clouds, with an average value of f ∼ 4 × 10-6 These abundances are in good agreement with predictions of ion-molecule models of interstellar chemistry in quiescent clouds which have reached steady state. The relatively high N2 concentrations suggest that the most of the nitrogen in dense clouds is in the form of molecular nitrogen. Given that the N2 abundances are comparable in both warm and cold clouds, condensation onto grains may not play a large role in the nitrogen chemistry of dense gas.
• Ziurys, L. M., Apponi, A. J., & Yoder, J. T. (1992). Detection of the quadrupole hyperfine structure in HCNH. Astrophysical Journal Letters, 397(2 PART 2), L123-L126.
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  Abstract: We report the first measurement of the electric quadrupole hyperfine structure of HCNH+ . The J = 1 → 0 transition of this interstellar molecular ion was observed toward the cold, dark cloud TMC-1, using the NRAO 12m telescope at 74 GHz. The three hyperfine components of this transition were clearly detected and resolved, enabling the first experimental determination of the quadrupole coupling constant eqQ of HCNH+. The value of this constant is calculated to be eqQ = -0.49 ± 0.07 MHz. The column density of HCNH+ toward TMC-1 was found to be Ntot, ∼ 2.8 × 1013 cm-2, corresponding to a fractional abundance relative to H2 of f ∼ 3 × 10-9. This abundance is at least one order of magnitude higher than the predictions of ionmolecule chemistry. Detection of the hyperfine structure clearly establishes the presence of HCNH+ in interstellar space.
• Ziurys, L. M., Barclay Jr., W. L., & Anderson, M. A. (1992). The millimeter-wave spectrum of the CaOH radical (X ²Σ⁺). Astrophysical Journal Letters, 384(2 PART 2), L63-L66.
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  Abstract: The pure rotational spectrum of the calcium hydroxide radical (CaOH) in its X 2Σ+(v = 0) ground state has been observed in the laboratory using millimeter/submillimeter direct absorption spectroscopy. CaOH was generated by the reaction of hydrogen peroxide with calcium vapor, produced in a Broida-type oven. Eleven rotational transitions of the species were measured in the range 80-320 GHz to an accuracy of ± 50 kHz. The spin-rotation splitting was readily observed in these data. The magnetic hyperfine structure due to the proton spin however was sufficiently small that it could not be resolved. The rotational and spin-rotation constants of CaOH were determined from a nonlinear least-squares fit to the data, using a 2Σ Hamiltonian. These laboratory measurements will now allow for an in-depth radio astronomical search for CaOH in interstellar clouds and circumstellar envelopes of late-type stars.
• Minh, Y. C., Ziurys, L. M., Irvine, W. M., & Mcgonagle, D. (1991). Abundances of hydrogen sulfide in star-forming regions. Astrophysical Journal Letters, 366(1), 192-197.
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  PMID: 11538287;Abstract: Interstellar hydrogen sulfide (H2S) and its isotopic variant H234S have been observed toward several star-forming regions via their 110-101 transitions at 2 mm, using the FCRAO telescope. In sources where both isotopic species H2S and H234S were observed, column densities of ∼1016 cm-2 were measured. Column density lower limits of ∼1014 cm-2 for H2S were found for other sources, where only the main isotopic line was observed. The fractional abundances of H2S relative to molecular hydrogen appear to be enhanced by at least an order of magnitude relative to quiescent cloud values (- 10-9) for many of the observed sources. Such enhancement toward star-forming clouds suggests that some process involving elevated temperature aids in producing this species; this could be gas-phase reactions, grain-related processes, or both.
• Shirley, J. E., Barclay Jr., W. L., Ziurys, L. M., & Steimle, T. C. (1991). A molecular beam millimeter-wave optical pump/probe study of the X ¹Σ⁺ state of yttrium monofluoride. Chemical Physics Letters, 183(5), 363-366.
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  Abstract: The J=4-3,J=5-4, andJ=6-5 pure rotational transitions in the ground X 1Σ+ state of yttrium monofluoride, YF, have been recorded by molecular beam millimeter-wave optical pump/probe spectroscopy. This study demonstrates that high resolution (
• Womack, M., Ziurys, L. M., & Wyckoff, S. (1991). N₂H⁺ in Orion: Chemical clues to the dynamics of the quiescent gas. Astrophysical Journal Letters, 370(2 PART 2), L99-L102.
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  Abstract: Measurements of the J = 1 → 0 transition of N2H+ have been obtained toward OMC-1 with high spectral resolution, using the NRAO 12 m telescope. In contrast with HCO+, N2H+ spectra exclusively exhibit the quiescent extended ridge gas toward Orion-KL. In fact, N2H+ appears to diminish in column density near the KL/IRc2 region, where many other molecules are quite abundant. Toward KL, the spectrum of N2H+ exhibits two narrow velocity components. One component lies to the northeast of Orion-KL with VLSR ∼9.5 km s-1, and the other lies southwest of KL with VLSR ∼7.2 km s-1. These data suggest that two clouds may be present in the region. Thus, N2H+ appears to be an excellent tracer of ambient, quiescent material. The velocity structure observed in this molecule toward KL may be related to the star formation observed in the Orion region.
• Ziurys, L. M., Mcgonagle, D., Minh, Y., & Irvine, W. M. (1991). Nitric oxide in star-forming regions: Further evidence for interstellar N-O bonds. Astrophysical Journal Letters, 373(2), 535-542.
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  PMID: 11538086;Abstract: Nitric oxide has been newly detected towards several star-forming clouds, including Orion-KL, Sgr B2(N), W33A, W51M, and DR21(OH) via its J = 3/2 → 1/2 transitions near 150 GHz, using the FCRAO 14 m telescope. Both λ-doubling components of NO were observed towards all sources. Column densities derived for nitric oxide in these clouds are N ∼ 1015-1016 cm-2, corresponding to fractional abundances of f∼ 0.5-1.0 × 10-8, relative to H2. Towards Orion-KL, the NO line profile suggests that the species arises primarily from hot, dense gas. Nitric oxide may arise from warm material toward the other clouds as well. Nitric oxide in star-forming regions could be synthesized by high-temperature reactions, although the observed abundances do not disagree with values predicted from low-temperature, ion-molecule chemistry by more than one order of magnitude. The abundance of NO, unlike other simple interstellar nitrogen compounds, does appear to be reproduced by chemical models, at least to a good approximation. Regardless of the nature of formation of NO, it appears to be a common constituent of warm, dense molecular clouds. N-O bonds may therefore be more prevalent than previously thought.
• McGonagle, D., Ziurys, L. M., Irvine, W. M., & Minh, Y. C. (1990). Detection of nitric oxide in the dark cloud L134N. Astrophysical Journal, 359(1), 121-124.
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  Abstract: We report the first detection of interstellar nitric oxide (NO) in a cold dark cloud, L134N. Nitric oxide was observed by means of its two 2Π1/2, J = 3/2 → 1/2, rotational transitions at 150.2 and 150.5 GHz, which occur because of Λ-doubling. The inferred column density for L134N is NNO ∼ 5 × 1014 cm-2 toward the SO peak in that cloud. This value corresponds to a fractional abundance relative to molecular hydrogen of fN0 ∼ 6 × 10-8 and is in good agreement with predictions of quiescent cloud ion-molecule chemistry. NO was not detected toward the dark cloud TMC-1 at an upper limit of fNO ≤ 3 ×10-8.
• McGonagle, D., Ziurys, L. M., Irvine, W. M., & Minh, Y. C. (1990). Detection of nitric oxide in the dark cloud L134N.. The Astrophysical journal, 359(1 Pt 1), 121-124.
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  PMID: 11538685;Abstract: We report the first detection of interstellar nitric oxide (NO) in a cold dark cloud, L134N. Nitric oxide was observed by means of its two 2 pi 1/2, J = 3/2 --> 1/2, rotational transitions at 150.2 and 150.5 GHz, which occur because of lambda-doubling. The inferred column density for L134N is N(NO) approximately 5 x 10(14) cm-2 toward the SO peak in that cloud. This value corresponds to a fractional abundance relative to molecular hydrogen of f(NO) approximately 6 x 10(-8) and is in good agreement with predictions of quiescent cloud ion-molecule chemistry. NO was not detected toward the dark cloud TMC-1 at an upper limit of f(NO) < or = 3 x 10(-8).
• Minh, Y. C., Ziurys, L. M., Irvine, W. M., & McGonagle, D. (1990). Observations of H2S toward OMC-1.. The Astrophysical journal, 360(1), 136-141.
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  PMID: 11538684;Abstract: Interstellar hydrogen sulfide (H2S) and its isotopic variant (H2(34)S) have been observed toward several positions in OMC-1 via their 1(10)-1(01) transitions near 168 GHz using the FCRAO 14 m telescope. We derive total column densities toward Orion(KL) for the extended ridge, for the plateau, and for the hot core, in addition to values for other positions in OMC-1. The fractional abundance of H2S (approximately 10(-9)) in the quiescent regions of OMC-1 seems to be difficult to explain by currently known ion-molecule reactions. The fractional abundance of H2S relative to H2 is enhanced by a factor of 1000 in the hot core and the plateau relative to the quiescent clouds. This enhancement may be a result of grain surface chemistry and/or of high-temperature gas-phase chemistry. From the nondetection of HDS in its 2(11)-2(12) transition, we estimate the abundance ratio [HDS]/H2S] < or = 0.02 in the hot core.
• Minh, Y. C., Ziurys, L. M., Irvine, W. M., & McGonagle, D. (1990). Observations of H₂S toward OMC-1. Astrophysical Journal, 360(1), 136-141.
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  Abstract: Interstellar hydrogen sulfide (H2S) and its isotopic variant (H234S) have been observed toward several positions in OMC-1 via their 110-101 transitions near 168 GHz using the FCRAO 14 m telescope. We derive total column densities toward Orion(KL) for the extended ridge, for the plateau, and for the hot core, in addition to values for other positions in OMC-1. The fractional abundance of H2S (∼ 10-9) in the quiescent regions of OMC-1 seems to be difficult to explain by currently known ion-molecule reactions. The fractional abundance of H2S relative to H2 is enhanced by a factor of 1000 in the hot core and the plateau relative to the quiescent clouds. This enhancement may be a result of grain surface chemistry and/or of high-temperature gas-phase chemistry. From the nondetection of HDS in its 211-212 transition, we estimate the abundance ratio [HDS]/[H2S] ≤ 0.02 in the hot core.
• Ziurys, L. M., Wilson, T. L., & Mauersberger, R. (1990). A new bipolar outflow source in OMC-1. Astrophysical Journal, 356(1 PART 2), L25-L29.
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  Abstract: Observations of the J = 2 → 1 and J = 5 → 4 transitions of SiO have been made toward the outflow source ∼1′.5 south of Orion-KL, using the IRAM 30 m telescope, with 25″ and 13″ resolution, respectively. Additional measurements of the J = 2 → 1, 3 → 2, and 5 → 4 lines of C34S and observations of J = 5 → 4 and J = 13 → 12 transitions of CH3CN have been made with the 30 m telescope. The SiO data clearly indicate that a separate outflow source exists ∼ 100″ S and 20″ W of the Orion-KL/IRc2 position, centered at α= 5h32m45s.4, δ= -5°26′5″.0 (1950.0). The outflow region has a FWHP size of ∼ 25″ and is bipolar in nature, the redshifted emission peaking ∼ 10″ S of the center and the blueshifted emission peaking 5″ N of center. The direction of the Orion-S flow is therefore NS, in contrast to Orion-KL, where the flow is oriented EW. The maximum outflow velocity (FWZP) is ∼ 25 km s-1. An LVG analysis of the SiO and CS data indicate that densities in the outflow are at least 3 × 105 cm-3. Kinetic temperatures derived from CH3CN are consistent with T ∼ 100 K. The Orion-S flow may be driven by a young, highly obscured star.
• Minh, Y. C., Irvine, W. M., & Ziurys, L. M. (1989). Detection of interstellar hydrogen sulfide in cold, dark clouds.. The Astrophysical journal, 345(1), L63-66.
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  PMID: 11538326;Abstract: We have detected interstellar hydrogen sulfide (H2S) toward the cold, dark clouds L134N and TMC 1. We derive total column densities of approximately 2.6 x 10(13) cm-2 and approximately 7.0 x 10(12) cm-2 at the SO peak of L134N and at the NH3 peak of TMC 1, respectively. Since the expected gas phase reactions leading to the formation of H2S are thought to be endothermic, grain surface reactions may play a major role in the synthesis of this species in cold, dark clouds. If the carbon abundance is high and grain surface reactions are the dominant formation route, H2CS would be expected to form instead of H2S, and the abundances of H2CS have been observed to be high where those of H2S are low in L134N and TMC 1.
• Ziurys, L. M., Friberg, P., & Irvine, W. M. (1989). Interstellar SiO as a tracer of high-temperature chemistry.. The Astrophysical journal, 343(1), 201-207.
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  PMID: 11538345;Abstract: The J = 2-1 transition of SiO has been searched for toward both hot and cold molecular gas. SiO was not detected toward the dark clouds TMC-1, L134 N, and B335, down to column density upper limits of N < 2-4 x 10(10) cm-2. The species, however, has been observed toward all sources with a kinetic temperature greater than or equal to 30 K, with the largest column densities (N approximately 10(13)-10(17) cm-2) measured in the warmest (TK > or = 100 K) material. The abundance of SiO, relative to HCN, is found to be approximately 0.1-1 in the massive star-forming regions toward Orion and NGC 7538; toward the dark clouds, the upper limits to this ratio is less than 0.0002-0.004. A similar enhancement in the warmer regions is reflected in the SiO/H2 ratio as well. A linear relation was found between the natural log of the SiO concentration and 1/TK, suggesting that the species' formation involves a chemically specific process that contains an activation barrier of approximately 90 K. SiO was also found to be underabundant with respect to SO in cold clouds, with SiO/SO < 1/1000, versus SiO/SO > or =, measured in Orion-KL. The formation of SiO is therefore linked closely to the local gas kinetic temperature, rather than the oxygen abundance, and its synthesis is likely to involve high-temperature gas-phase reactions. The species thus may serve as an unambiguous indicator of high-temperature or "shock" chemistry.
• Ziurys, L. M., Snell, R. L., & Dickman, R. L. (1989). Shock chemistry in the molecular clouds associated with SNR IC 443.. The Astrophysical journal, 341(2), 857-866.
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  PMID: 11538348;Abstract: Several interstellar molecules have been detected toward the highly perturbed B and G clouds associated with the supernova remnant IC 443 via their 3 mm transitions, including N2H+, SiO, SO, CN, HNC, and H13CO+. The (J, K) = (1, 1) and (2, 2) inversion lines of metastable ammonia have also been observed, as well as the J = 3-2 transition of HCO+ at 1.2 mm. Analysis of the (1, 1) and (2, 2) inversion lines of NH3 indicates minimum gas kinetic temperatures of TK = 70 K toward cloud B, and TK = 33 K in cloud G. Modeling of the J = 1-0 and J = 3-2 transitions of HCO+ implies densities greater than 10(5) cm-3 toward both positions. These data clearly show that hot and dense material is present in IC 443, and they suggest the presence of shocks in both regions. A careful analysis of the HCO+ lines indicates that the HCO+ abundance is at most enhanced by factors of a few over that found in cold, quiescent gas. This conclusion contradicts past claims of HCO+ abundance enhancements of several orders of magnitude in the perturbed regions. The N2H+ abundance was also found to be similar to that in cold gas, suggesting that there is no increase in ionization in the clouds. The abundances of SO and CS, as well as CN and NH3, do not appear to differ significantly from those found in cold dark clouds, although chemistry models predict sulfur-containing species to undergo high-temperature enhancements. SiO, however, is found to have an abundance in the perturbed gas 100 times larger than the upper limits observed in the dark cloud TMC 1, a result in agreement with high temperature chemistry models. In addition, the HNC/HCN ratio in both IC 443 B and G was found to be approximately 0.1--far from the ratio of 1 predicted by low-temperature ion-molecule chemistry, but similar to the values observed in clouds where elevated temperatures are present.
• Irvine, W. M., Avery, L. W., Friberg, P., Matthews, H. E., & Ziurys, L. M. (1988). Newly detected molecules in dense interstellar clouds.. Astrophysical letters & communications, 26, 167-180.
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  PMID: 11538461;Abstract: The last year or so has seen the identification of several new interstellar molecules, including C2S, C3S, C5H, C6H, and (probably) HC2CHO in the cold, dark cloud TMC-1; and the discovery of the first interstellar phosphorous-containing molecule, PN, in the Orion "plateau" source. Further interesting results include the observations of 13C3H2 and C3HD, and the first detection of HCOOH (formic acid) in a cold cloud.
• Irvine, W. M., Friberg, P., Hjalmarson, A., Ishikawa, S., Kaifu, N., Kawaguchi, K., Madden, S. C., Matthews, H. E., Ohishi, M., Saito, S., Suzuki, H., Thaddeus, P., Turner, B. E., Yamamoto, S., & Ziurys, L. M. (1988). Identification of the interstellar cyanomethyl radical (CH2CN) in the molecular clouds TMC-1 and Sagittarius B2.. The Astrophysical journal, 334(2), L107-111.
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  PMID: 11538463;Abstract: We report the astronomical identification of the cyanomethyl radical, CH2CN, the heaviest nonlinear molecular radical to be identified in interstellar clouds. The complex fine and hyperfine structures of the lowest rotational transitions at about 20.12 and 40.24 GHz are resolved in TMC-1, where the abundance appears to be about 5 x 10(-9) relative to that of H2. This is significantly greater than the observed abundance of CH3CN (methyl cyanide) in TMC-1. In Sgr B2 the hyperfine structure is blended in the higher frequency transitions at 40, 80, and 100 GHz, although the spin-rotation doubling is clearly evident. Preliminary searches in other sources indicate that the distribution of CH2CN is similar to that for such carbon chain species as HC3N or C4H.
• Minh, Y. C., Irvine, W. M., & Ziurys, L. M. (1988). Observations of interstellar HOCO+: abundance enhancements toward the galactic center.. The Astrophysical journal, 334(1), 175-181.
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  PMID: 11538465;Abstract: A survey of the 4(04)-3(03) and 1(01)-0(00) transitions of HOCO+ has been made toward several molecular clouds. The HOCO+ molecule was not observed in any sources except Sgr B2 and Sgr A. The 5(05)-4(04) and 4(14)-3(13) transitions were also detected toward Sgr B2. The results indicate that gas phase CO2 is not a major carbon reservoir in typical molecular clouds. In Sgr B2, the HOCO+ antenna temperature exhibits a peak approximately 2' north of the Sgr B2 central position (Sgr B2[M]) and the 4(04)-3(03) line emission is extended over a approximately 10' x 10' region. The column density of HOCO+ at the northern peak in Sgr B2 is approximately 3 x 10(14) cm-2, and the fractional abundance relative to H2 > or = 3 x 10(-10), which is about 2 orders of magnitude greater than recent predictions of quiescent cloud ion-molecule chemistry.
• Saito, S., Yamamoto, S., Irvine, W. M., Ziurys, L. M., Suzuki, H., Ohishi, M., & Kaifu, N. (1988). Laboratory detection of a new interstellar free radical CH2CN(2B1).. The Astrophysical journal, 334(2), L113-116.
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  PMID: 11538464;Abstract: An asymmetric-top free radical CH2CN, which as a 2B1 ground state, was detected for the first time by laboratory microwave spectroscopy. The radical was produced in a free-space absorption cell by a DC glow discharge in pure CH3CN gas. About 60 fine-structure components were observed for the N = 11-10 to 14-13 a-type rotational transitions in the frequency region of 220-260 GHz, and many hyperfine resolved components for the N = 4-3 and 5-4 transitions in the 80 and 100 GHz regions, respectively. The molecular constants, including the rotational constants, centrifugal distortion constants, and spin-rotation coupling constants with centrifugal distortion correction terms were determined from the fine-structure resolved transitions, and the hyperfine coupling constants due to the hydrogen and nitrogen nuclei were obtained from the low-N transitions. As a result we assigned U100602 and U80484 from Sgr B2, and U40240 and U20120 from TMC-1, to the N = 5-4, 4-3, 2-1, and 1-0 transitions with K-1 = 0 of the CH2CN radical.
• Schenewerk, M. S., Snyder, L. E., Hollis, J. M., Jewell, P. R., & Ziurys, L. M. (1988). HCO emission from H II-molecular cloud interface regions.. The Astrophysical journal, 328(2), 785-796.
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  PMID: 11538466;Abstract: A survey of well-known molecular clouds in the four strongest HCO NK-,K+ = 1(01)-0(00) hyperfine transitions has been carried out to determine the prevalence of HCO and to study its chemistry. HCO emission was observed in seven molecular clouds. Three of these, NGC 2264, W49, and NGC 7538, were not previously known sources of HCO. In addition, NGC 2024 and Sgr B2 were mapped and shown to have extensive HCO emission. The survey results show the HCO abundance to be enhanced in H II-molecular cloud interface regions and support a correlation between C+ and HCO emission. The strength of the HCO emission in NGC 2024 is interpreted in terms of this enhancement and the source structure and proximity to Earth.
• Ziurys, L. M. (1988). SiS in Orion-KL: evidence for "outflow" chemistry.. The Astrophysical journal, 324(1), 544-552.
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  PMID: 11538468;Abstract: SiS has been conclusively detected toward Orion-KL via its J = 6-5 and J = 5-4 rotational transitions at 91 and 109 GHz. Line profiles indicate that the species is present at an LSR velocity of 7.5 km s-1 with a half-width at zero power of 36 km s-1. Such characteristics associate SiS with the moderate velocity outflow (V approximately 18 km s-1) centered on IRc2 and observed in thermal SiO, the NH3 "plateau," and OH, H2O, and SiO masers. The column density estimated for SiS in this region is Ntot = 4 x 10(15) cm-2, corresponding to a fractional abundance of f approximately 4 x 10(-9). Such an abundance implies an SiO/SiS ratio of approximately 60 in the outflow material, remarkably close to the cosmic O/S ratio of approximately 40 and contrasting with the SiO/SiS value of > approximately 10(3) predicted by ion-molecule models. This difference is probably a result of the high temperatures and densities present in the outflow, which favor thermal equilibrium abundances similar to those observed in the circumstellar shells of late-type stars rather than "ion-molecule"-type concentrations. In addition to SiS, some twenty new unidentified lines near 91 and 109 GHz were detected toward KL, as well as transitions arising from HC5N, HC13CCN, HCC13CN, O13CS, and, possibly, CH3CH2OH, CH3CHO, and CH3OD.
• Ziurys, L. M. (1987). Detection of interstellar PN: the first phosphorus-bearing species observed in molecular clouds.. The Astrophysical journal, 321(1 Pt 2), L81-85.
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  PMID: 11542218;Abstract: Phosphorus nitride (PN) has been detected in the interstellar medium. The J = 2-1, 3-2, 5-4, and 6-5 rotational lines of this species have been observed toward Orion-KL, and the J = 2-1 transition in Sgr B2 and W51. The PN line profiles in Orion indicate that the molecule's emission arises from the "plateau" or "doughnut" region associated with the outflow from IRc2. The species is thus primarily present in hot, dense gas. Column densities derived for PN toward Orion-KL are 3-4 X 10(13) cm-2, but may be as high as 10(14) cm-2, if the species is located in a 10" region. These column densities imply a fractional abundance for PN in the Orion "plateau" of approximately 1-4 X 10(-10). Such a large abundance for phosphorus nitride is not predicted by quiescent cloud ion-molecule chemistry and suggests that high-temperature processes are responsible for the synthesis of PN in the KL outflow.
• Wootten, A., Boulanger, F., Bogey, M., Combes, F., Encrenaz, P. J., Gerin, M., & Ziurys, L. (1986). A search for interstellar H3O+.. Astronomy and astrophysics, 166, L15-18.
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  PMID: 11542067;Abstract: The P (2,1) line of H3O+, the hydroxonium ion, a key species in ion-molecule chemistry, has been sought in the interstellar medium and in Halley's Comet. In OMC1 and SgrB2, a line was detected which may possibly be attributed to H3O+. Verification of this identification must be accomplished through observation of the P(3,2) line at 364 GHz, or detection of isotopic variants. If we were to assume that the detected line arises from H3O+, we can deduce a fractional abundance X(H3O+) in OMC1 and SgrB2 of approximately 10(-9) and a production rate in Comet Halley of Q(H3O+) 10(28)s-1. These results would place H3O+ among the more abundant molecular ions in the interstellar gas in agreement with theoretical predictions.
• Ziurys, L. M., & Turner, B. E. (1986). Detection of interstellar vibrationally excited HCN.. The Astrophysical journal, 300(1), L19-23.
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  PMID: 11542068;Abstract: Vibrationally excited HCN has been observed for the first time in the interstellar medium. The J = 3-2 rotational transitions of the l-doubled (0,1(1d,1c), 0) bending mode of HCN have been detected toward Orion-KL and IRC +10216. In Orion, the overall column density in the (0,1,0) mode, which exclusively samples the "hot core", is 1.7 x 10(16) cm-2 and can be understood in terms of the "doughnut" model for Orion. The ground-state HCN column density implied by the excited-state observations is 2.3 x 10(18) cm-2 in the hot core, at least one order of magnitude greater than the column densities derived for HCN in its spike and plateau/doughnut components. Radiative excitation by 14 micrometers flux from IRc2 accounts for the (0,1,0) population, provided the hot core is approximately 6-7 x 10(16) cm distant from IRc2, in agreement with the "cavity" model for KL. Toward IRC +10216 we have detected J = 3-2 transitions of both (0,1(1c),(1d), 0) and (0, 2(0), 0) excited states. The spectral profiles have been modeled to yield abundances and excitation conditions throughout the expanding envelope.
• Ziurys, L. M., & Turner, B. E. (1986). HCNH+: a new interstellar molecular ion.. The Astrophysical journal, 302, L31-36.
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  PMID: 11542069;Abstract: A new molecular ion, HCNH+, or protonated HCN, has been detected in the interstellar medium. The J = 1-0, 2-1, and 3-2 rotational transitions of this species have been observed toward Sgr B2. Using a large velocity gradient model calculation, the column density of HCNH+ is found to be approximately 4 x 10(14) cm-2, about one order of magnitude less than that estimated for HCO+ and HCN in this source. Such a column density implies a fractional abundance for HCNH+ in Sgr B2 of approximately 3 x 10(-10), one to several orders of magnitude greater than the values predicted by ion-molecule models of interstellar chemistry. The high observed abundance of this species, relative to theoretical calculations, suggests that the destruction of HCNH+ by dissociative recombination is slower than expected, or that the formation rate of the ion has been underestimated.
• Lewis, E. S., Walker, B. J., & Ziurys, L. M. (1978). Methyltriphenoxyphosphonium trifluoromethanesulphonate: A new, versatile synthetic reagent. Journal of the Chemical Society, Chemical Communications, 424-425.
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  Abstract: Methyltriphenoxyphosphonium trifluoromethanesulphonate is used to synthesise a variety of compound types including ethers, esters, nitriles, and diols and in a novel reduction of alkenes to alkanes.
• Monts, D. L., Ziurys, L. M., Beck, S. M., Liverman, M. G., & Smalley, R. E. (1976). Rotational and vibrational analysis of the B̃←X̃ system of XeF as observed in a supersonic free jet. The Journal of Chemical Physics, 71(10), 4057-4065.
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  Abstract: The fluorescence excitation spectrum of XeF cooled in a supersonic expansion with helium has been observed for the wavelength region 2860 to 3205 Å. The cold spectrum displays well-resolved rotational structure for seven of the XeF isotopic species. Analysis of this rotational structure is reported for υ′ = 16-21 in the B̃ (Ω = 1/2) state and for υ″ = 0 and 1 in the X̃ 2∑+ state. Vibrational intervals have been measured for individual XeF isotopes with an accuracy of ±0.50 cm-1 for vibrational levels υ′ = 11-22 and ±0.37 cm-1 for υ″ = 0-2. © 1979 American Institute of Physics.

Proceedings Publications

• Ziurys, L. M., & Halfen, D. T. (2015, june). The Sub-millimeter/THz Spectrum of AlH (X1Σ+), CrH (X1Σ+), and SH+( X3Σ-). In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., & Schmidt, D. R. (2015, june). CCH and HNC in Planetary Nebulae. In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., & Schmidt, D. R. (2015, june). First Scientific Observations with the New ALMA Prototype Antenna of the Arizona Radio Observatory: HCN and CCH in the Helix Nebula. In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Burkhardt, A., Booth, S., Remijan, A., & Carroll, B. (2015, june). Mapping the Spatial Distribution of Metal-Bearing Oxides in VY Canis Majoris. In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Emerson, N., Folkers, T., Freund, R., Reiland, G., & Forbes, D. (2015, june). The New ALMA Prototype 12 m Telescope of the Arizona Radio Observatory: Transport, Commissioning, and First Light. In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Lincowski, A. P., & Halfen, D. T. (2015, june). Pure Rotational Spectra of the Rare Isotopologues of TiO (X3Δr). In 70h International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Zack, L. N., Bucchino, M. P., Young, J., Binns, M., & Sheridan, P. M. (2015, june). Hyperfine-Resolved Pure Rotational Spectroscopy of ScN (X1Σ+), YN (X1Σ+), and BaNH (X1Σ+): Insight into Metal-Nitrogen Bonding. In 70h International Symposium on Molecular Spectroscopy.
• Contreras, C., Velilla, L., Alcolea, J., Quintana-Lacaci, G., Cernicharo, J., Agundez, M., Teyssier, D., Bujarrabal, V., Castro-Carrizo, A., Daniel, F., Fonfria, J. P., Garcia-Lario, P., Goicoechea, J. R., Herpin, F., Barlow, M., Cherchneff, I., Comito, C., Cordiner, M., Decin, L., , Halfen, D. .., et al. (2014, apr). Mm-wave and far-IR Molecular line survey of OH 231.8+4.2: Hard-boiled rotten eggs. In Asymmetrical Planetary Nebulae VI conference, Proceedings of the conference held 4-8 November, 2013. Edited by C. Morisset, G. Delgado-Inglada and S. Torres-Peimbert. Online at http://www.astroscu.unam.mx/apn6/PROCEEDINGS/, id.88.
• Freund, R. W., Ziurys, L. M., Lauria, E. F., & Reiland, G. P. (2014, 2014). The Arizona Radio Observatory: A New 12-M Telescope and Other Developments. In 2014 XXXITH URSI GENERAL ASSEMBLY AND SCIENTIFIC SYMPOSIUM (URSI GASS).
• Ziurys, L. M. (2014, March). Exotic Chemistry in Circumstellar Environments: Laboratory and Astronomical Studies. In 247th American Chemical Society National Meeting, Symposium Chemistry in the Interstellar Medium (PHYS008).
• Ziurys, L. M., & Bucchino, M. P. (2014, june). Laboratory Detection of ClZnCH3 (X1A1): Further Evidence for Zinc Insertion. In 69th International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., & Bucchino, M. P. (2014, june). Laboratory Spectroscopy of Metal Hydride Molecules: A Window on Diffuse Cloud Chemistry. In 97th Canadian Chemistry Conference and Exhibition, Symposium Chemistry at Cold Temperatures and Interstellar Chemistry.
• Ziurys, L. M., & Edwards, J. (2014, june). Comparative Chemistry in Planetary Nebulae: The Role of the Carbon to Oxygen Ratio. In 69th International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., & Edwards, J. (2014, june). Molecular Abundances in the Circumstellar Envelope of the Oxygen-Rich Supergiant VY Canis Majoris. In 69th International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Bucchino, M. P., Sheridan, P. M., & Young, J. P. (2014, june). Millimeter-Wave Studies of the Isotopologues of IZnCH3 (X1A1): Geometric Parameters and Evidence for Zinc Insertion. In 69th International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., Dattini, N. S., Zack, L. N., Johnson, E. R., & LeRoy, R. (2014, june). Analytical Empirical Potentials for All Stable Isotopolgues of the Ground (X1Σ+) State of ZnO from Purely Rotational Measurements. In 69th International Symposium on Molecular Spectroscopy.
• Adande, G., & Ziurys, L. M. (2013, jun). Distribution of SO2 and SO in the Envelope of Vy-Canis Majoris: Insight Into Circumstellar Sulfur Chemistry. In 68th International Symposium on Molecular Spectroscopy.
• Adande, G., & Ziurys, L. M. (2013, jun). The Millimeter Direct Absorption and Fourier Transform Microwave Spectrum of Vanadium Sulfide (X ^$ $4$ $$ Sigma$ ^$ $-$ $). In 68th International Symposium on Molecular Spectroscopy.
• Anderson, J. K., & Ziurys, L. M. (2013, jun). Exploring Shock Chemistry in Orion-Kl with Mid-J Molecular Transitions. In 68th International Symposium on Molecular Spectroscopy.
• Anderson, J. K., Ziurys, L. M., & Herpin, F. (2013, jun). Formation of CH ^$ $+$ $: Shock Chemistry in NGC 7027. In 68th International Symposium on Molecular Spectroscopy.
• Bucchino, M. P., & Ziurys, L. M. (2013, jun). Terahertz Spectroscopy of CaH (X ^$ $2$ $$ Sigma$ ^$ $+$ $), MgH (X ^$ $2$ $$ Sigma$ ^$ $+$ $), and ZnH (X ^$ $2$ $$ Sigma$ ^$ $+$ $) : Extreme Hydride Synthesis. In 68th International Symposium on Molecular Spectroscopy.
• Bucchino, M. P., Young, J. P., Sheridan, P. M., & Ziurys, L. M. (2013, jun). Laboratory Detection of IZnCH _$ $3$ $ (X ^$ $1$ $A _$ $1$ $) : Further Evidence for Zinc Insertion. In 68th International Symposium on Molecular Spectroscopy.
• Bucchino, M. P., Young, J. P., Sheridan, P. M., Ewing, D., & Ziurys, L. M. (2013, jun). Further Studies of Potassium-Bearing Molecules : the Millimeter-Wave Spectrum of KSH (X ^$ $1$ $A ^'). In 68th International Symposium on Molecular Spectroscopy.
• Doeleman, S., Fish, V. L., Schenck, D., Beaudoin, C., Blundell, R., Bower, G. C., Broderick, A. E., Chamberlin, R., Freund, R., Friberg, P., Gurwell, M. A., Ho, P. T., Honma, M., Inoue, M., Krichbaum, T., Lamb, J. W., Loeb, A., Lonsdale, C. J., Marrone, D. P., , Moran, J. M., et al. (2013, jan). Jet-Launching Structure Resolved Near the Supermassive Black Hole in M87. In American Astronomical Society Meeting Abstracts, 221, #123.07.
• Edwards, J. L., & Ziurys, L. M. (2013, June). Mapping the Molecular Outflows of the High Excitation Red SPIDER Nebula (ngc 6537). In 68th International Symposium on Molecular Spectroscopy.
• Edwards, J. L., & Ziurys, L. M. (2013, June). The First Extensive Molecular Study of AN Oxygen-Rich Planetary Nebula: Observations of SiO, SO _2, and SO. In 68th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., & Ziurys, L. M. (2013, jun). A New E-Band (60 - 90 GHz) Fourier Transform Millimeter-Wave Spectrometer. In 68th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., & Ziurys, L. M. (2013, jun). New Results from a Spectral-Line Survey of Sgr B2(N): Insight Into Gas-Phase Processes. In 68th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2013, jun). The Fourier Transform Microwave/millimeter Spectrum of ScO (X ^2$ Sigma$ ^+). In 68th International Symposium on Molecular Spectroscopy.
• Lu, R., Fish, V. L., Weintroub, J., Doeleman, S., Bower, G. C., Freund, R., Friberg, P., Ho, P. T., Honma, M., Inoue, M., Jorstad, S. G., Krichbaum, T., Marrone, D. P., Marscher, A. P., Moran, J. M., Oyama, T., Plambeck, R. L., Primiani, R., Shen, Z., , Tilanus, R., et al. (2013, jan). Fine Scale Structure of AGN Jets with 1.3 mm VLBI. In American Astronomical Society Meeting Abstracts, 221, #143.05.
• Min, J., & Ziurys, L. M. (2013, jun). Millimeter and Sub-Millimeter Spectroscopy of CrCCH (X ^$ $6$ $$ Sigma$ ^+). In 68th International Symposium on Molecular Spectroscopy.
• Schmidt, D. R., & Ziurys, L. M. (2013, jun). A Search for HCO+ and HCN Emission in Planetary Nebulae. In 68th International Symposium on Molecular Spectroscopy.
• Zeigler, N. R., Ziurys, L. M., & Zack, L. N. (2013, jun). Structure of the Dense Molecular Gas in the Helix Nebula: Large Scale Mapping of HCO+. In 68th International Symposium on Molecular Spectroscopy.
• Anderson, J. K., Halfen, D. T., & Ziurys, L. M. (2012, jun). The CCN (tilde$ $X$ $$^2$$ pi$$_1/2$) Radical Revisited: New Fourier Transform Microwave Measurements. In 67th International Symposium on Molecular Spectroscopy.
• Bucchino, M. P., & Ziurys, L. M. (2012, jun). Sub-Millimeter Spectroscopy of FeH and FeD (X$^4$$ Delta$$_i$). In 67th International Symposium on Molecular Spectroscopy.
• Edwards, J. L., Ziurys, L. M., Cox, E. G., & Woolf, N. J. (2012, jun). The Molecular Content of Planetary Nebulae: the Dumbbell and the Red SPIDER. In 67th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., & Ziurys, L. M. (2012, jun). The Fourier Transform Microwave Spectrum of Yoh and Yod ( $ $X$ $ ^1$ Sigma$ ^ +). In 67th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2012, jun). Fourier Transform Microwave Spectrum of the AlC _2 ( $ $X$ $ ^2A _1) Radical. In 67th International Symposium on Molecular Spectroscopy.
• Halfen, D. T., Min, J., & Ziurys, L. M. (2012, jun). a New U-Band (40 - 60 GHz) Fourier Transform Microwave Spectrometer. In 67th International Symposium on Molecular Spectroscopy.
• Min, J., Halfen, D. T., & Ziurys, L. M. (2012, jun). Laboratory Detection and Microwave Spectrum of ScC _2 Radical (X ^2A _1). In 67th International Symposium on Molecular Spectroscopy.
• Sheridan, P. M., Binns, M. K., Young, J. P., Bucchino, M. P., & Ziurys, L. M. (2012, jun). Fourier Transform Microwave Spectroscopy of Alkali Metal Hydrosulfides: Detection of Ksh. In 67th International Symposium on Molecular Spectroscopy.
• Zack, L. N., Zeigler, N. R., & Ziurys, L. M. (2012, jun). Molecular Content of the Helix Nebula. In 67th International Symposium on Molecular Spectroscopy.
• Ziurys, L. M., & Gilles, A. (2012, April). New Measurements of the 14N/15N Ratios in Interstellar Clouds, Circumstellar Gas, and Supernova Remnants Using Millimeter Astronomy. In Astrobiology Science Conference 2012: Exploring Life: Past, Past, Near and Far.
• Ziurys, L. M., & Halfen, D. T. (2012, April). Establishing the Complete Inventory of Complex Organic Molecules in an Interstellar Cloud. In Astrobiology Science Conference 2012: Exploring Life: Past, Past, Near and Far.
• Ziurys, L. M., Adande, G. R., & Halfen, D. T. (2012, jun). Fourier Transform Microwave Spectroscopy of ScS (X$^2$$ Sigma$), YS (X$^2$$ Sigma$) and VS (X$^4$$ Sigma$). In 67th International Symposium on Molecular Spectroscopy.

Presentations

• Schmidt, D. R., Ziurys, L. M., Egan, S., & Sinclair, A. (2020, June). The Amazing Molecular Content of Planetary Nebulae: Detections of HCN and HCO+ in Nine New Sources. 236th Meeting of the American Astronomical Society.
• Singh, A. P., Ziurys, L. M., & Edwards, J. L. (2020, June). Complex Chemistry and Dynamics the Circumstellar Envelope of the Supergiant NML Cygnus. 236th Meeting of the American Astronomical Society.
• Zega, T. J., & Ziurys, L. M. (2020, June). Phosphorous in Chondritic Meteorites: Beyond Schreibersite. 236th Meeting of the American Astronomical Society.
• Ziurys, L. M. (2020, December). The Unexpected Chemistry in Planetary Nebulae: From CO to C60. American Chemical Society AstroCheminar Series.
• Ziurys, L. M. (2020, February). The Unexpected Chemistry in Planetary Nebulae. Institute for Theoretical Atomic, Molecular, and Optical Physics Winter School Astrochemistry.
• Ziurys, L. M. (2020, February). The Unique Chemistry of Dying Stars: Refractory Elements, Grains, and Isotopes. Institute for Theoretical Atomic, Molecular, and Optical Physics Winter School Astrochemistry.
• Ziurys, L. M. (2020, June). Chemistry Between the Stars: The Emerging Field of Astrochemistry. U.S. National Chemistry Olympiad, ACS Summer Study Camp.
• Ziurys, L. M., Burton, M. A., & Zega, T. J. (2020, June). Laboratory Detection of the SiP Radical and Astronomical Search. 236th Meeting of the American Astronomical Society.
• Bernal, J. J., Ziurys, L. M., & Humphreys, R. M. (2019, June). Identification of VO (X4Σ-) in the Envelope of VY CMa: A New Circumstellar Molecule. 74th International Symposium on Molecular Spectroscopy.
• Bernal, J. J., Ziurys, L. M., Haenecour, P., Howe, J., & et al, . (2019, June). Formation of Interstellar C60 from Silicon Carbide Circumstellar Grains. 234th Meeting of the American Astronomical Society.
• Bernal, J. J., Ziurys, L. M., Haenecour, P., Howe, J., & et al, . (2019, June). Formation of Interstellar C60 from Silicon Carbide Circumstellar Grains. 74th International Symposium on Molecular Spectroscopy.
• Burton, M. A., Russ, B. T., Bucchino, M. P., Ziurys, L. M., & et al, . (2019, June). Fourier Transform Microwave Spectroscopy of LiNH2 and NaNH2 (X1A1): Comparing Quadrupole Interactions. 74th International Symposium on Molecular Spectroscopy.
• Herman, T. J., & Ziurys, L. M. (2019, June). The 3d Bromine Series: The Pure Rotational Spectrum of CrBr (X6Σ+). 74th International Symposium on Molecular Spectroscopy.
• Humphreys, R., Ziurys, L. M., Helton, L. A., Gordon, M. S., & et al, . (2019, January). Recent High Mass Loss Events in the Extreme Red Supergiant VY CMa. 233rd Meeting of the American Astronomical Society.
• Zega, T. J., Bernal, J. J., Howe, J. Y., Ziurys, L. M., & et al, . (2019, August). Putting Stars in the Gap: In Situ Irradiation and Heating of Synthetic SiC and Implications for the Origins of C-Rich Circumstellar Materials. Microscopy and Microanalyis 2019.
• Zega, T. J., Bernal, J. J., Howe, J. Y., Ziurys, L. M., & et al, . (2019, March). In Situ Irradiation and Heating of Synthetic SiC and Implications for the Origins of C-rich Circumstellar Materials. 50th Lunar and Planetary Science Conference.
• Ziurys, L. M. (2019, June). Cold Molecules and the Chemistry in Space. Gordon Research Conference on Atomic Physics.
• Ziurys, L. M. (2019, October). The Unique Chemistry of Dying Stars: Organics, Metals, and Fullerenes. Colloquium, Dept. of Chemistry, University of Virginia.
• Ziurys, L. M. (2019, September). Molecules, Nanotubes and Materials in the Extreme Environment of Interstellar Space. Materials Science and Technology Conference 2019.
• Bernal, J. J., Bose, M., & Ziurys, L. M. (2018, June). Constraining Sulfur Isotope Abundances in Molecular Clouds: A Meteoritic Perspective. 73rd International Symposium on Molecular Spectroscopy.
• Burton, M. A., & Ziurys, L. M. (2018, June). Rotational and Isotopic Study of the ZnBr Radical (X2Σ+). 73rd International Symposium on Molecular Spectroscopy.
• Burton, M. A., Halfen, D. T., & Ziurys, L. M. (2018, June). Millimeter/Submillimeter Spectroscopy of the CrP Radical (X4Σ-). 73rd International Symposium on Molecular Spectroscopy.
• Burton, M. A., Russ, B., Sheridan, P. M., Bucchino, M., & Ziurys, L. M. (2018, June). Millimeter-Wave Spectroscopy of KO: Establishing the Electronic Ground State. 73rd International Symposium on Molecular Spectroscopy.
• Halfen, D. T., & Ziurys, L. M. (2018, June). The Pure Rotational Spectrum of the T-Shaped AlC2 Radical (X2A1). 73rd International Symposium on Molecular Spectroscopy.
• Halfen, D. T., Burton, M. A., DeYonker, N., Clouthier, D. J., & Ziurys, L. M. (2018, March). Quantum Mechanical Calculations on Metal-Bearing Dicarbides and Experimental Verification. 255th National Meeting of the American Chemical Society.
• Keogh, J. p., Halfen, D. T., & Ziurys, L. M. (2018, June). The Millimeter/Submillimeter Spectrum of F2SO (X1A′). 73rd International Symposium on Molecular Spectroscopy.
• Schmidt, D. R., & Ziurys, L. M. (2018, July). The Surprising Molecular and Isotopic Content of Planetary Nebulae. XIII Rencontres Du Vietnam: The Cosmic Cycle of Dust and Gas in the Galaxy.
• Schmidt, D. R., Adande, G. R., & Ziurys, L. M. (2018, March). Modeling of the Chemistry in the Complex Outflows of Supergiant Stars. 255th National Meeting of the American Chemical Society.
• Schmidt, D. R., Zack, L. N., & Ziurys, L. M. (2018, June). Hydrocarbon Chemistry in Planetary Nebulae: Observations of CCH and c-C3H2. 232nd Meeting of the American Astronomical Society.
• Ziurys, L. M. (2018, April). Chemistry Among the Stars: The Unexpected Molecular Environment Beyond Earth. 21st Annual Robert W. Murray Lecture, University of Missouri-St. Louis.
• Ziurys, L. M. (2018, August). New Instrumental and Synthetic Developments in Rotational Spectroscopy: A Focus on Metal-Bearing Radicals. 256th National Meeting of the American Chemical Society.
• Ziurys, L. M. (2018, March). High Resolution Spectroscopy of Metal-Containing Free Radicals: Gaining Insight into Metal-Ligand Bonding. 27th Austin Symposium on Molecular Structure and Dynamics.
• Ziurys, L. M. (2018, May). Probing the Molecular Universe with Rotational Spectroscopy: A Laboratory and Observational Perspective. 49th Meeting of the American Physical Society Division of Atomic, Molecular, and Optical Physics.
• Ziurys, L. M. (2018, October). A Molecular View of the Late Stages of Stellar Evolution: Millimeter Observations of Supergiants and Planetary Nebulae. Colloquium, Dept. of Physics and Astronomy, University of Minnesota, Minneapolis/St. Paul.
• Ziurys, L. M. (2018, September). Following the Chemical History of Stellar Ejecta through Molecular Observations and Laboratory Spectroscopy. Joint NASA/NSF Lab Astrophysics PI Meeting.
• Ziurys, L. M., Halfen, D. T., Burton, M. A., McCarthy, M. C., Gottlieb, C. A., Lee, K., & Stancil, P. (2018, June). Laboratory Rotational Spectroscopy in the Era of ALMA: Applications to Disks and Circumstellar Flows. 232nd Meeting of the American Astronomical Society.
• Ziurys, L. M., Schmidt, D. R., Woolf, N. J., & Zega, T. J. (2018, August). Observational Constraints for Pre-Solar Grains: Carbon and Nitrogen Isotope Ratios in Dying Stars. Goldschmidt Conference, Session: Presolar Grains, Nucleosynthesis and Isotope Anomalies as Cosmic Fingerprint.
• Ziurys, L. M., Schmidt, D. R., Zack, L. N., & Woolf, N. J. (2018, March). The Unusual Dynamics and Chemistry in Planetary Nebulae. 255th National Meeting of the American Chemical Society.
• Bernal, J. J., Schmidt, D. R., & Ziurys, L. M. (2017, June). Phosphorus Chemistry in Oxygen-Rich Stars. 72nd International Symposium on Molecular Spectroscopy.
• Burton, M., Kilchenstein, K. M., & Ziurys, L. M. (2017, June). The Millimeter-Wave Spectrum of MgI (X2Σ+). 72nd International Symposium on Molecular Spectroscopy.
• Burton, M., Russ, B., Sheridan, P. M., Bucchino, M. P., & Ziurys, L. M. (2017, June). The Pure Rotational Spectrum of KO. 72nd International Symposium on Molecular Spectroscopy.
• Freund, R. W., Ziurys, L. M., Forbes, D. C., Folkers, T. W., & Lauria, E. F. (2017, August). Capability Improvements at the Arizona Radio Observatory. XXXII URSI General Assembly and Scientific Symposium.
• Halfen, D. T., & Ziurys, L. M. (2017, June). The 12C/13C Ratio in the Galactic Center: Implications for Galactic Chemical Evolution and Isotope Chemistry. 72nd International Symposium on Molecular Spectroscopy.
• Halfen, D. T., Bernal, J. J., & Ziurys, L. M. (2017, April). Comparison of Gas Phase and Condensed Phase Species: SgrB2(N) vs. Comet 67P. 253rd National Meeting of the American Chemical Society.
• Ziurys, L. M. (2017, June). Connecting the Interstellar Medium to the Solar System: Carbon, Molecules and Isotopes. Colloquium, Lowell Observatory.
• Ziurys, L. M. (2017, November). The Primordial Carbon Cycle: Carriers, Pathways and Assembly Leading to Prebiotic Molecules. IAU Symposium of Astrobiology.
• Ziurys, L. M. (2017, October). Our Increasingly Molecular Universe: Using Microwave, Millimeter and Terahertz Spectroscopy to Probe Interstellar Chemistry. Colloquium, Dept. of Chemistry, Rhodes College.
• Ziurys, L. M. (2017, October). Our Increasingly Molecular Universe: Using Microwave, Millimeter and Terahertz Spectroscopy to Probe Interstellar Chemistry. Colloquium, Dept. of Chemistry, University of Memphis.
• Ziurys, L. M., Halfen, D. T., & Zega, T. (2017, April). Extreme Isotope Ratios in Meteoritic Material: A Gas-Phase Interstellar Origin?. 253rd National Meeting of the American Chemical Society.
• Ziurys, L. M., Woolf, N. J., Schmidt, D. R., Zack, L. N., & Zega, T. J. (2017, July). C and N Isotope Ratios in Dying Stars: Implications for Pre-solar Grains. 80th Annual Meeting of The Meteoritical Society.
• Ziurys, L. M. (2015, Aug). Pursuing Free Radicals with Big Trucks, Large Cranes… And Some Sanity: The Arizona APA Project. 33rd International Symposium of Free Radicals.
• Ziurys, L. M. (2015, Feb). Following the Chemical History of Stellar Ejecta through Astronomical Observations and Laboratory Spectroscopy. Second Workshop on Experimental Laboratory Astrophysics.
• Ziurys, L. M. (2015, May). Arizona Radio Observatory: Current Status and New Developments. Special Colloquium, Radio Group, Dept. of Astronomy, University of Maryland.
• Ziurys, L. M. (2015, Oct). Heavenly (and Earthly) Rotational Spectroscopy of Transient Molecules: from the Microwave to THz Regimes. Modern Optics and Spectroscopy Seminar Series, MIT.
• Ziurys, L. M. (2015, Sept). Interstellar Chemistry in the Astrobiological Context. Meeting of the Astronomische Gesellschaft (AG): From the First Quasars to Life-Bearing Planets: From Accretion Physics to Astrobiology,.
• Ziurys, L. M. (2014, Aug). Linking the Molecular History of the Interstellar Medium to the Solar System through Radio Astronomy. Lunar and Planetary Lab Conference.
• Ziurys, L. M. (2014, July). Prebiotic Chemical Evolution in the Astrophysical Context. International Society for the Studies of the Origins of Life (ISSOL) and IAU Commission 51 Bioastronomy Joint Conference: Origins 2014.
• Ziurys, L. M. (2014, June). Molecules Hiding in Dying Stars: The Rich Chemistry Associated with Planetary Nebulae. 97th Canadian Chemistry Conference and Exhibition, Symposium Chemistry at Cold Temperatures and Interstellar Chemistry.
• Ziurys, L. M. (2014, May). Tracing the Molecular History of the Interstellar Medium through Millimeter Astronomy and Laboratory Spectroscopy. Astrochemistry Colloquium, Radboud University.
• Ziurys, L. M. (2014, Nov). Status of the ALMA Prototype Antenna: Arizona Radio Observatory. Special Report, ALMA Group, European Southern Observatory (ESO).
• Ziurys, L. M. (2014, sept). Status Report: APA Project, Arizona Radio Observatory. Special Report, National Science Foundation.
• Ziurys, L. M. (2013, April). Chemistry Beyond the Solar System: Spectroscopic Studies of Interstellar Molecules. Chemistry Colloquium, Dept. of Chemistry, Swarthmore College.
• Ziurys, L. M. (2013, May). ALMA Band 2: Future Prospects for Scientific Studies. ALMA Band 2 Science Workshop.
• Ziurys, L. M. (2013, May). The 14N/15N Ratio Across the Galaxy. Nordic Astrobiology Network Conference: Isotopes as Diagnostic Tools in Astronomy, Geology, and Biology.
• Ziurys, L. M. (2013, October). The Molecular Content of Planetary Nebulae. International Space Studies Institute Workshop: The Methane Balance – Formation and Destruction Processes on Planets, Their Satellites, and the Interstellar Medium.
• Ziurys, L. M. (2012, April). Organic Molecules in Planetary Nebulae: Linking Circumstellar Ejecta to the ISM. Astrobiology Science Conference 2012: Exploring Life Past, Past, Near and Far, Session: Organic Continuum from the ISM to Early Earth.
• Ziurys, L. M. (2012, Jan). Event Horizon Telescope Site Developments: Arizona Radio Observatory. Scientific Workshop :Bringing Black Holes into Focus: The Event Horizon Telescope.
• Ziurys, L. M. (2012, June). Molecules in Evolved Planetary Nebulae. Nordic Astrobiology Network and EU COST Joint Conference: The Warm Universe: Astrochemistry at Intermediate and Elevated Temperatures.

Poster Presentations

• Ziurys, L. M., Bernal, J. J., Schmidt, D. R., & Zega, T. J. (2018, September). Unexpected Molecules in Planetary Nebulae: Implications for C60 and C60+ in Diffuse Clouds. 2nd International Workshop on Cosmic Fullerenes.
• Ziurys, L. M., & Schmidt, D. R. (2015, Aug). Carbon Chemistry in Planetary Nebulae: Observations of the CCH Radical. IAU Symposium 315: From Interstellar Clouds to Star-forming Galaxies: Universal Processes, Focus Meeting 4: Planetary Nebulae as Probes of Galactic Structure and Evolution.
• Ziurys, L. M., & Schmidt, D. R. (2015, Aug). Polyatomic Molecules in Planetary Nebulae: A Survey of HCN and HCO+. IAU Symposium 315: From Interstellar Clouds to Star-forming Galaxies: Universal Processes, Focus Meeting 4: Planetary Nebulae as Probes of Galactic Structure and Evolution.
• Ziurys, L. M., Halfen, D. T., & Bucchino, M. P. (2015, Aug). Submillimeter/THz Spectroscopy of Molecular Hydride Radicals. 33rd International Symposium of Free Radicals.
• DeYonker, N. J., Halfen, D. T., Ziurys, L. M., & Allen, W. D. (2014, MAR 16). Electronic structure of vanadium monochloride cation (VCl+): At the crossroads of experimental and computational astrochemistry. ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY.
• Ziurys, L. M., & Min, J. (2013, July). Pure Rotational Spectroscopy of Chromium-Containing Radicals. 32nd International Symposium on Free Radicals.
• Ziurys, L. M., Halfen, D. T., & Min, J. (2013, July). Fourier Transform Microwave/Millimeter-Wave Spectroscopy of Metal-Containing Dicarbide Radicals. 32nd International Symposium on Free Radicals.
• Ziurys, L. M., Zack, L. N., Bucchino, M. P., & Maier, J. P. (2012, sept). Hyperfine Structure in Transition Metal Nitrides: ScN (X1Σ+) and YN (X1Σ+). 22nd International Conference on High Resolution Molecular Spectroscopy.