Stephen G Kukolich

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• Tanjaroon, C., Zhou, Z., Mills, D., Keck, K., & Kukolich, S. G. (2021). Corrections and Additions to "Microwave Spectra and Theoretical Calculations for Two Structural Isomers of Methylmanganese Pentacarbonyl". Inorganic chemistry, 60(2), 1274-1275.
• Tanjaroon, C., Zhou, Z., Mills, D., Keck, K., & Kukolich, S. G. (2020). Microwave Spectra and Theoretical Calculations for Two Structural Isomers of Methylmanganese Pentacarbonyl. Inorganic chemistry, 59(9), 6432-6438.
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  The first microwave rotational spectra for two structural isomers of methylmanganese pentacarbonyl were measured in the 4-9 GHz range using a pulsed-beam Fourier transform microwave spectrometer. The spectra for the two isomers, a symmetric-top structure and an asymmetric-top acyl isomeric structure, were fit to obtain rotational and centrifugal distortion constants and Mn quadrupole coupling parameters. The rotational constants, the manganese (Mn) nuclear quadrupole coupling constant, the centrifugal distortion constants, and the spin-rotation constant were determined for the symmetric CHMn(CO) and have the following values: = = 793.153(3) MHz, = 0.00040(4) MHz, = 0.0018(2) MHz, = 0.183(6) MHz, and eQq= -87.4(3) MHz. Rotational constants and Mn quadruple coupling constants were determined for the isomeric acyl-CHC(O)Mn(CO) and have the following values: = 839.96(4) MHz, = 774.20(7) MHz, = 625.63(1) MHz, and 1.5 eQq= 44.9(47) MHz and 0.25(eQq - eQq) = 11.9(12) MHz. The measured rotational constants from the isomeric acyl-CHC(O)Mn(CO) were compared with various theoretical computations. The calculated rotational constants for the dihapto-acyl and the agostic-acyl structures are reasonably close to the experimental values. We note that the calculated dihapto-acyl structure most closely matches the experimental data, as the calculation for the dihapto structure using the B3LYP functional with the aug-cc-pVDZ basis set closely reproduced the experimental values for , , and .
• Kukolich, S. G. (2019). Synthesis, microwave spectra, x-ray structure and high-level theoretical calculations for formamidinium formate. J. Chem. Phys., 150, 094305. doi:10.1063/1.5081683
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  Research paper
• Zhou, Z., Aitken, R. A., Cardinaud, C., Slawin, A. M., Wang, H., Daly, A. M., Palmer, M. H., & Kukolich, S. G. (2019). Synthesis, microwave spectra, x-ray structure, and high-level theoretical calculations for formamidinium formate. The Journal of chemical physics, 150(9), 094305.
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  An efficient synthesis of formamidinium formate is described. The experimental x-ray structure shows both internal and external H-bonding to surrounding molecules. However, in the gas phase, this compound occurs as a doubly hydrogen bonded dimer between formamidine and formic acid. This doubly hydrogen-bonded structure is quite different from the solid state structure. Microwave spectra were measured in the 6-14 GHz range using a pulsed-beam Fourier transform microwave (MW) spectrometer. The two nonequivalent N-atoms exhibit distinct quadrupole coupling. The rotational, centrifugal distortion, and quadrupole coupling constants determined from the spectra have the following values: A = 5880.05(2), B = 2148.7710(2), C = 1575.23473(13), 1.5 χaa (N1) = 1.715(3), 0.5(χbb-χcc) (N1) = -1.333(4), 1.5 χaa (N2) = 0.381(2), 0.25(χbb-χcc) (N2) = -0.0324(2), and D = 0.002145(5) MHz. The experimental inertial defect, Δ = -0.243 amu Å, is consistent with a planar structure. Accurate and precise rotational constants (A, B, and C), obtained from the MW measurements, were closely reproduced, within 1%-2% of the measured values, with the M11 DFT theoretical calculations. Detailed comparison of the measured and calculated A, B, and C rotational constants confirms the planar doubly hydrogen bonded structure. The calculated nitrogen quadrupole coupling strengths of the monomer are quite different from either of the two nitrogen sites of the dimer. The poor agreement between measured and calculated quadrupole coupling strengths shows that the dimer is not locked in the equilibrium structure but is likely undergoing large amplitude vibrational motion of the hydrogen atoms moving between the N and O atoms involved in the hydrogen bonding.
• Pejlovas, A. M., Zhou, Z., Ashe, A. J., & Kukolich, S. G. (2018). Microwave Spectra, Structure, and the Aromatic Character of 1-Chloroborepin. The journal of physical chemistry. A, 122(6), 1542-1549.
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  High resolution microwave spectra for the somewhat unstable compound 1-chloroborepin were measured in the 5-10 GHz range using a pulsed beam Fourier transform microwave spectrometer. Transitions were assigned and measured for three isotopologues, which include the most abundant isotopologue,BCl, and the less abundantBCl andBCl isotopologues. The molecular parameters (MHz) determined for theBCl isotopologue are A = 3490.905(35), B = 1159.38520(79), C = 870.59492(56), 1.5χ(B) = -0.220(22), 0.25(χ- χ) (B) = -1.5300(99), 1.5χ(Cl) = -54.572(33), and 0.25(χ- χ) (Cl) = 4.7740(79). The inertial defect is calculated to be Δ = -0.174 amu Åfrom the experimental rotational constants, indicating a planar structure with some out of plane vibrational motion. An extended Townes-Dailey analysis was performed on theB andCl nuclei to determine the electron occupations in the valence hybridized orbitals using the experimental quadrupole coupling strengths. From the analysis it was determined that Cl is sharing some electron density with the empty p-orbital on B. The B-Cl bond length determined from the data is 1.798(1) Å, and the B-C bond lengths are 1.533(10) Å. The structural parameters and electronic structure properties of 1-chloroborepin are consistent with an aromatic boron-containing molecule.
• Kukolich, S. G. (2017). Rotational spectrum and structure of the T-shaped cyanoacetylene carbon dioxide complex, HCCCN•••CO2. J. Mol. Spectrosc., 342, 62-72. doi:http://dx.doi.org/10.1016/j.jms.2017.07.001
• Kukolich, S. G. (2017). The microwave spectrum of ferrocenecarboxylic acid. J. Mol. Spectrosc, 338, 77-80. doi:https://doi.org/10.1016/j.jms.2017.06.011
• Kukolich, S. G. (2016). Microwave measurements of the rotational spectrum and gas phase structural parameters of the maleimide – formic acid dimer. J. Mol. Spectrosc, 321, 1-4. doi:http://dx.doi.org/10.1016/j.jms.2016.01.011
• Kukolich, S. G. (2016). Microwave rotational spectrum and gas phase structural parameters of maleimide. J. Mol. Spectrosc., 319, 26-29. doi:http://dx.doi.org/10.1016/j.jms.2015.12.004
• Kukolich, S. G. (2016). Microwave rotational spectrum and gas phase structural parameters of maleimide. J. Mol. Spectrosc, 319, 26-29. doi:http://dx.doi.org/10.1016/j.jms.2015.12.004
• Kukolich, S. G. (2016). Rotational spectra and nitrogen nuclear quadrupole coupling for the cyanoacetylene dimer. J. Mol. Spectrosc, 321, 5-12. doi:http://dx.doi.org/10.1016/j.jms.2016.01.008
• Pejlovas, A. M., Daly, A. M., Ashe, A. J., & Kukolich, S. G. (2016). Microwave spectra, molecular structure, and aromatic character of 4a,8a-azaboranaphthalene. The Journal of chemical physics, 144(11), 114303.
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  The microwave spectra for seven unique isotopologues of 4a,8a-azaboranaphthalene [hereafter referred to as BN-naphthalene] were measured using a pulsed-beam Fourier transform microwave spectrometer. Spectra were obtained for the normal isotopologues with (10)B, (11)B, and all unique single (13)C and the (15)N isotopologue (with (11)B), in natural abundance. The rotational, centrifugal distortion and quadrupole coupling constants determined for the (11)B(14)N isotopologue are A = 3042.712 75(43) MHz, B = 1202.706 57(35) MHz, C = 862.220 13(35) MHz, DJ = 0.06(1) kHz, 1.5χaa ((14)N) = 2.5781(61) MHz, 0.25(χbb - χcc) ((14)N) = - 0.1185(17) MHz, 1.5χaa (11B) = - 3.9221(75) MHz, and 0.25(χbb - χcc) ((11)B) = - 0.9069(24) MHz. The experimental inertial defect is Δ = - 0.159 amu Å(2), which is consistent with a planar structure for the molecule. The B-N bond length from the experimentally determined structure is 1.47 Å, which indicates π-bonding character between the B and N. The measured quadrupole coupling strengths provide important and useful information about the bonding, orbital occupancy, and aromatic character for this aromatic molecule. Extended Townes-Dailey analyses were used to determine the B and N electron sp(2)-hybridized and p-orbital occupations. These results are compared with electron orbital occupations from the natural bond orbital option in theoretical calculations. From the analyses, it was determined that BN-naphthalene has aromatic character similar to that of other N-containing aromatics. The results are compared with similar results for B-N bonding in 1,2-dihydro-1,2-azaborine and BN-cyclohexene. Accurate and precise structural parameters were obtained from the microwave measurements on seven isotopologues and from high-level G09 calculations.
• Pejlovas, A. M., Serrato, A., Lin, W., & Kukolich, S. G. (2016). Microwave measurements of the tropolone-formic acid doubly hydrogen bonded dimer. The Journal of chemical physics, 144(4), 044306.
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  The microwave spectrum was measured for the doubly hydrogen bonded dimer formed between tropolone and formic acid. The predicted symmetry of this dimer was C2v(M), and it was expected that the concerted proton tunneling motion would be observed. After measuring 25 a- and b-type rotational transitions, no splittings which could be associated with a concerted double proton tunneling motion were observed. The calculated barrier to the proton tunneling motion is near 15 000 cm(-1), which would likely make the tunneling frequencies too small to observe in the microwave spectra. The rotational and centrifugal distortion constants determined from the measured transitions were A = 2180.7186(98) MHz, B = 470.873 90(25) MHz, C = 387.689 84(22) MHz, DJ = 0.0100(14) kHz, DJK = 0.102(28) kHz, and DK = 13.2(81) kHz. The B3LYP/aug-cc-pVTZ calculated rotational constants were within 1% of the experimentally determined values.
• Daly, A. M., Carey, S. J., Pejlovas, A. M., Li, K., Kang, L., & Kukolich, S. G. (2015). Gas phase measurements of mono-fluoro-benzoic acids and the dimer of 3-fluoro-benzoic acid. The Journal of chemical physics, 142(14), 144303.
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  The microwave spectrum of the mono-fluoro-benzoic acids, 2-fluoro-, 3-fluoro-, and 4-fluoro-benzoic acid have been measured in the frequency range of 4-14 GHz using a pulsed beam Fourier transform microwave spectrometer. Measured rotational transition lines were assigned and fit using a rigid rotor Hamiltonian. Assignments were made for 3 conformers of 2-fluorobenzoic acid, 2 conformers of 3-fluorobenzoic acid, and 1 conformer of 4-fluorobenzoic acid. Additionally, the gas phase homodimer of 3-fluorobenzoic acid was detected, and the spectra showed evidence of proton tunneling. Experimental rotational constants are A(0(+)) = 1151.8(5), B(0(+)) = 100.3(5), C(0(+)) = 87.64(3) MHz and A(0(-)) = 1152.2(5), B(0(-)) = 100.7(5), C(0(-)) = 88.85(3) MHz for the two ground vibrational states split by the proton tunneling motion. The tunneling splitting (ΔE) is approximately 560 MHz. This homodimer appears to be the largest carboxylic acid dimer observed with F-T microwave spectroscopy.
• Pejlovas, A. M., Barfield, M., & Kukolich, S. G. (2015). Microwave measurements of the spectra and molecular structure for the monoenolic tautomer of 1,2- cyclohexanedione. The journal of physical chemistry. A, 119(9), 1464-8.
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  The microwave spectrum for the monoenolic tautomer of 1,2-cyclohexanedione was measured in the 4-14 GHz regime using a pulsed-beam Fourier transform (PBFT), Flygare-Balle-type microwave spectrometer. The molecular structure and moments of inertia were initially calculated using Gaussian 09 using MP2 and 6-311++G** basis sets, and these calculations were used to predict the rotational constants and microwave spectra. Rotational transition frequencies were measured and used to determine rotational constants (A, B, and C) and centrifugal distortion constants (DJ and DK). The rotational constants for the parent isotopologue, one singly substituted deuterium and six singly substituted (13)C isotopologues, were used in a least-squares fit to determine gas-phase structural parameters for this molecule. All hydrogen atoms were held fixed to the calculated positions, as well as the carbon atoms at positions 1 and 10 and the oxygen atoms at positions 6 and 7. The rotational constants for the parent isotopologue are A = 3161.6006(12), B = 2101.5426(3), and C = 1320.7976(4) MHz. The distortion constants obtained from the fit are DJ = 0.0436 and DK = 0.436 kHz. Structural parameters from the MP2 calculations are in fair agreement with the measured parameters.
• Pejlovas, A. M., Lin, W., & Kukolich, S. G. (2015). Microwave Spectrum for a Second Higher Energy Conformer of Cyclopropanecarboxylic Acid and Determination of the Gas Phase Structure of the Ground State. The journal of physical chemistry. A, 119(39), 10016-21.
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  Microwave spectra for a higher-energy conformer of cyclopropanecarboxylic acid (CPCA) were measured using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer. The rotational constants (in megahertz) and centrifugal distortion constants (in kilohertz) for this higher-energy conformer are A = 7452.3132(57), B = 2789.8602(43), C = 2415.0725(40), DJ = 0.29(53), and DJK = 2.5(12). Differences between rotational constants for this excited-state conformation and the ground state are primarily due to the acidic OH bond moving from a position cis relative to the cyclopropyl group about the C1-C9 bond to the more stable trans conformation. Calculations indicate that the relative abundance of the higher-energy state should be 15% to 17% at room temperature, but the observed relative abundance for the supersonic expansion conditions is about 1%. The measurements of rotational transitions for the trans form of CPCA were extended to include all of the unique (13)C singly substituted positions. These measurements, along with previously measured transitions of the parent and -OD isotopologues, were used to determine a best-fit gas-phase structure.
• Pejlovas, A. M., Lin, W., & Kukolich, S. G. (2015). Microwave spectra and structure of the cyclopropanecarboxylic acid-formic acid dimer. The Journal of chemical physics, 143(12), 124311.
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  The rotational spectrum of the cyclopropanecarboxylic acid-formic acid doubly hydrogen bonded dimer has been measured in the 4-11 GHz region using a Flygare-Balle type pulsed-beam Fourier transform microwave spectrometer. Rotational transitions were measured for the parent, four unique singly substituted (13)C isotopologues, and a singly deuterated isotopologue. Splittings due to a possible concerted double proton tunneling motion were not observed. Rotational constants (A, B, and C) and centrifugal distortion constants (DJ and DJK) were determined from the measured transitions for the dimer. The values of the rotational (in MHz) and centrifugal distortion constants (in kHz) for the parent isotopologue are A = 4045.4193(16), B = 740.583 80(14), C = 658.567 60(23), DJ = 0.0499(16), and DJK = 0.108(14). A partial gas phase structure of the dimer was derived from the rotational constants of the measured isotopologues, previous structural work on each monomer units and results of the calculations.
• Sun, M., Sargus, B. A., Carey, S. J., & Kukolich, S. G. (2015). Measurements of deuterium quadrupole coupling in propiolic acid and fluorobenzenes using pulsed-beam Fourier transform microwave spectrometers. The Journal of chemical physics, 142(15), 154306.
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  The pure rotational spectra of deuterated propiolic acids (HCCCOOD and DCCCOOH), 1-fluorobenzene (4-d1), and 1,2-difluorobenzene (4-d1) in their ground states have been measured using two Fourier transform microwave (FTMW) spectrometers at the University of Arizona. For 1-fluorobenzene (4-d1), nine hyperfine lines of three different ΔJ = 0 and 1 transitions were measured to check the synthesis method and resolution. For 1,2-difluorobenzene (4-d1), we obtained 44 hyperfine transitions from 1 to 12 GHz, including 14 different ΔJ = 0, 1 transitions. Deuterium quadrupole coupling constants along the three principal inertia axes were well determined. For deuterated propiolic acids, 37 hyperfine lines of Pro-OD and 59 hyperfine lines of Pro-CD, covering 11 and 12 different ΔJ = - 1, 0, 1 transitions, respectively, were obtained from 5 to 16 GHz. Deuterium quadrupole coupling constants along the three inertia axes were well resolved for Pro-OD. For Pro-CD, only eQq(aa) was determined due to the near coincidence of the CD bond and the least principal inertia axis. Some measurements were made using a newer FTMW spectrometer employing multiple free induction decays as well as background subtraction. For 1-fluorobenzene (4-d1) and 1,2-difluorobenzene (4-d1), a very large-cavity (1.2 m mirror dia.) spectrometer yielded very high resolution (2 kHz) spectra.
• Daly, A., Cossairt, B., Southwood, G., Carey, S., Cummins, C., & Kukolich, S. (2012). Microwave spectrum of arsenic triphosphide. J. Mol. Spectroscopy, 211(1), 82-85.
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  DOI:10.1016/j.jms.2012.03.007
• Kukolich, S. G., Mitchell, E. G., Carey, S. J., Sun, M., & Sargus, B. A. (2013). Microwave structure for the propiolic acid-formic acid complex. Journal of Physical Chemistry A, 117(39), 9525-9530.
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  Abstract: New microwave spectra were measured to obtain rotational constants and centrifugal distortion constants for the DCCCOOH⋯HOOCH and HCCCOOD⋯DOOCH isotopologues. Rotational transitions were measured in the frequency range of 4.9-15.4 GHz, providing accurate rotational constants, which, combined with previous rotational constants, allowed an improved structural fit for the propiolic acid-formic acid complex. The new structural fit yields reasonably accurate orientations for both the propiolic and formic acid monomers in the complex and more accurate structural parameters describing the hydrogen bonding. The structure is planar, with a positive inertial defect of Δ = 1.33 amu Å2. The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations. The best-fit hydrogen bond lengths have an r(O1-H1⋯O4) of 1.64 Å and an r(O3-H2⋯O2) of 1.87 Å. The average of the two hydrogen bond lengths is rav(exp) = 1.76 Å, in good agreement with rav(theory) = 1.72 Å. The center of mass separation of the monomers is RCM = 3.864 Å. Other structural parameters from the least-squares fit using the experimental rotational constants are compared with theoretical values. The spectra were obtained using two different pulsed beam Fourier transform microwave spectrometers. © 2013 American Chemical Society.
• Kukolich, S. G., Mitchell, E. G., Carey, S. J., Sun, M., & Sargus, B. A. (2013). Microwave structure for the propiolic acid-formic acid complex. The journal of physical chemistry. A, 117(39), 9525-30.
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  New microwave spectra were measured to obtain rotational constants and centrifugal distortion constants for the DCCCOOH···HOOCH and HCCCOOD···DOOCH isotopologues. Rotational transitions were measured in the frequency range of 4.9-15.4 GHz, providing accurate rotational constants, which, combined with previous rotational constants, allowed an improved structural fit for the propiolic acid-formic acid complex. The new structural fit yields reasonably accurate orientations for both the propiolic and formic acid monomers in the complex and more accurate structural parameters describing the hydrogen bonding. The structure is planar, with a positive inertial defect of Δ = 1.33 amu Å(2). The experimental structure exhibits a greater asymmetry for the two hydrogen bond lengths than was obtained from the ab initio mp2 calculations. The best-fit hydrogen bond lengths have an r(O1-H1···O4) of 1.64 Å and an r(O3-H2···O2) of 1.87 Å. The average of the two hydrogen bond lengths is r(av)(exp) = 1.76 Å, in good agreement with r(av)(theory) = 1.72 Å. The center of mass separation of the monomers is R(CM) = 3.864 Å. Other structural parameters from the least-squares fit using the experimental rotational constants are compared with theoretical values. The spectra were obtained using two different pulsed beam Fourier transform microwave spectrometers.
• Kukolich, S., Sun, M., Wang, Y., Carey, S. J., Mitchell, E. G., Bowman, J., & Kukolich, S. G. (2013). Calculations and measurements of the deuterium tunneling frequency in the propiolic acid-formic acid dimer and description of a newly constructed Fourier transform microwave spectrometer. The Journal of chemical physics, 139(8).
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  The concerted proton tunneling frequency for the propiolic acid-formic acid dimer was calculated using a relaxed ab initio double-well potential in the imaginary-frequency mode of the saddle point, and new measurements were made for the deuterated propiolic acid-formic acid (ProOD-FAOD) isotopologue. It is important to have consistent calculated tunneling frequency values between normal and deuterated isotopologues since parameters can be readily adjusted to get good agreement with one isotopologue. High-resolution rotational spectra of deuterated (ProOD-FAOD) dimer were measured using a newly constructed Fourier Transform microwave spectrometer. The new spectrometer has mirror size: 30 cm in diameter with a radius of curvature of 59 cm and is equipped with multiple-FID data collection (5-10 FID's for each gas pulse). For the deuterated (ProOD-FAOD) isotopologue, 45 rotational lines (a type: 34; b type: 11) were measured in the lowest tunneling states range between 6.5 GHz and 15.5 GHz. With the new high-resolution measurements of the tunneling doublets (b-dipole transitions), the double potential well responsible for the deuterium tunneling was depicted much more precisely. The two tunneling states are separated by 3.48 MHz. The rotational constants obtained in this work are quite helpful for further structure analysis as well.
• Sun, M., Wang, Y., Carey, S. J., Mitchell, E. G., Bowman, J., & Kukolich, S. G. (2013). Calculations and measurements of the deuterium tunneling frequency in the propiolic acid-formic acid dimer and description of a newly constructed Fourier transform microwave spectrometer. Journal of Chemical Physics, 139(8).
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  PMID: 24007006;Abstract: The concerted proton tunneling frequency for the propiolic acid-formic acid dimer was calculated using a relaxed ab initio double-well potential in the imaginary-frequency mode of the saddle point, and new measurements were made for the deuterated propiolic acid-formic acid (ProOD-FAOD) isotopologue. It is important to have consistent calculated tunneling frequency values between normal and deuterated isotopologues since parameters can be readily adjusted to get good agreement with one isotopologue. High-resolution rotational spectra of deuterated (ProOD-FAOD) dimer were measured using a newly constructed Fourier Transform microwave spectrometer. The new spectrometer has mirror size: 30 cm in diameter with a radius of curvature of 59 cm and is equipped with multiple-FID data collection (5-10 FID's for each gas pulse). For the deuterated (ProOD-FAOD) isotopologue, 45 rotational lines (a type: 34; b type: 11) were measured in the lowest tunneling states range between 6.5 GHz and 15.5 GHz. With the new high-resolution measurements of the tunneling doublets (b-dipole transitions), the double potential well responsible for the deuterium tunneling was depicted much more precisely. The two tunneling states are separated by 3.48 MHz. The rotational constants obtained in this work are quite helpful for further structure analysis as well. © 2013 AIP Publishing LLC.
• Daly, A. M., Cossairt, B. M., Southwood, G., Carey, S. J., Cummins, C. C., & Kukolich, S. G. (2012). Microwave spectrum of arsenic triphosphide. Journal of Molecular Spectroscopy, 278(1), 68-71.
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  Abstract: The microwave spectrum of AsP 3 has been measured and assignments for three different vibrational states have been made. The symmetric top ΔJ = +1 transitions have been fit to obtain rotational constants, centrifugal distortion constants and quadrupole coupling strengths for the three vibrational states (I-III), B I = 2201.394(1) MHz, eQqaaI = 48.728(5) MHz, DJI = 0.2(3) kHz, DJKI = 0.5(1) kHz and σ I = 4 kHz, B II = 2192.26(1) MHz, eQqaaII = 48.62(4) MHz, B III = 2183.93(2) MHz, eQqaaIII = 48.53(4) MHz. The experimental vibration-rotation coupling constant, α(ν 4) = 9.20(3) MHz is compared with results from MP2/6-311G calculations. The excited states (II and III) are tentatively assigned to the ν 4 and 2ν 4 excited vibrational states. © 2012 Elsevier Inc. All rights reserved.
• Daly, A. M., Douglass, K. O., Sarkozy, L. C., Neill, J. L., Muckle, M. T., Zaleski, D. P., Pate, B. H., & Kukolich, S. G. (2011). Microwave measurements of proton tunneling and structural parameters for the propiolic acid-formic acid dimer. Journal of Chemical Physics, 135(15).
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  PMID: 22029310;Abstract: Microwave spectra of the propiolic acid-formic acid doubly hydrogen bonded complex were measured in the 1 GHz to 21 GHz range using four different Fourier transform spectrometers. Rotational spectra for seven isotopologues were obtained. For the parent isotopologue, a total of 138 a-dipole transitions and 28 b-dipole transitions were measured for which the a-dipole transitions exhibited splittings of a few MHz into pairs of lines and the b-type dipole transitions were split by ∼580 MHz. The transitions assigned to this complex were fit to obtain rotational and distortion constants for both tunneling levels: A0 = 6005.289(8), B0+ = 930.553(8), C0+ = 803.9948(6) MHz, Δ0+J = 0.075(1), Δ0+JK = 0.71(1), and δ0+j = -0.010(1) kHz and A0- = 6005.275(8), B0- = 930.546(8), C0- = 803.9907(5) MHz, δ0-J = 0.076(1), Δ0-JK 0.70(2), and δ0-j = -0.008(1) kHz. Double resonance experiments were used on some transitions to verify assignments and to obtain splittings for cases when the b-dipole transitions were difficult to measure. The experimental difference in energy between the two tunneling states is 291.428(5) MHz for proton-proton exchange and 3.35(2) MHz for the deuterium-deuterium exchange. The vibration-rotation coupling constant between the two levels, Fab, is 120.7(2) MHz for the proton-proton exchange. With one deuterium atom substituted in either of the hydrogen-bonding protons, the tunneling splittings were not observed for a-dipole transitions, supporting the assignment of the splitting to the concerted proton tunneling motion. The spectra were obtained using three Flygare-Balle type spectrometers and one chirped-pulse machine at the University of Virginia. Rotational constants and centrifugal distortion constants were obtained for HCOOH⋯HOOCCCH, H13COOH⋯HOOCCCH, HCOOD⋯HOOCCCH, HCOOH⋯DOOCCCH, HCOOD⋯DOOCCCH, DCOOH⋯HOOCCCH, and DCOOD⋯HOOCCCH. High-level ab initio calculations provided initial rotational constants for the complex, structural parameters, and some details of the proton tunneling potential energy surface. A least squares fit to the isotopic data reveals a planar structure that is slightly asymmetric in the OH distances. The formic OH⋯O propiolic hydrogen bond length is 1.8Å and the propiolic OH⋯O formic hydrogen bond length is 1.6Å, for the equilibrium configuration. The magnitude of the dipole moment was experimentally determined to be 1.95(3) × 10 -30 C m (0.584(8) D) for the 0+ states and 1.92(5)×10-30 C m (0.576(14) D) for the 0- states. © 2011 American Institute of Physics.
• Daly, A. M., Lavin, C. M., Weidenschilling, E. S., Holden, A. M., & Kukolich, S. G. (2011). Microwave spectra, ab initio and DFT calculations and molecular structure for (η⁷-cycloheptatriene)Ti(η⁵-cyclopentadienyl) and (η⁷-cycloheptatriene)Cr(η⁵-cyclopentadienyl). Journal of Molecular Spectroscopy, 267(1-2), 172-177.
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  Abstract: Microwave spectra of 1-d-(η7-cycloheptatriene) 48Ti(η5-cyclopentadienyl) (CHT-Ti-Cp) and two singly substituted 13C isotopomers were measured and gas phase structural parameters were determined. Rotational transitions were also measured for (η7-cycloheptatriene)52Cr(η5- cyclopentadienyl). Rotational constants for the Ti complex were found to be A = 1720(4) MHz, B = 769.269(1) MHz and C = 766.131(1) MHz and for [ 13CC6H7-48Ti-C5H 5], A = 1773(2) MHz, B = 769.6931(4) MHz and C = 761.1789(5) MHz and for [1-d-C7H648TiC5H5] and A = 1270(5) MHz, B = 767.0142(9) MHz and C = 765.323(1) MHz for [C 7H748Ti13CC4H 5]. A structural analysis for the (CHT-Ti-Cp) data showed that the cycloheptatriene ring protons droop towards titanium as predicted by DFT and MP2 calculations. The droop of the protons toward the metal was experimentally determined to be 8.0(2)°out of the plane of the cycloheptatriene ring. The ring center distance to titanium was found to be 2.01(3) for Ti-Cp and 1.48(3) for Ti-CHT using a least squares fit to the measured rotational constants and fixing many of the structural parameters to the calculated values. The spectrum of the normal isotopomer (η7-cycloheptatriene) Ti(η5-cyclopentadienyl) was re-measured and a discussion of the possible 47Ti quadrupole coupling constants is presented. The chromium analog K = 0 spectrum was analyzed to obtain B = 851.229 MHz, and DJ = 0.028(6) kHz. Results from structure calculations are reported and discussed for (CHT-M-Cp) complexes with M = Ti, Cr, Zr, Hf, Mo, W using MP2, B3PW91 and B3LYP methods. © 2011 Elsevier Inc. All rights reserved.
• Daly, A. M., Mitchell, E. G., Sanchez, D. A., Block, E., & Kukolich, S. G. (2011). Microwave spectra and gas phase structural parameters for N-hydroxypyridine-2(1H)-thione. Journal of Physical Chemistry A, 115(50), 14526-14530.
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  PMID: 22070758;Abstract: The microwave spectrum for N-hydroxypyri-dine-2(1H)-thione (pyrithione) was measured in the frequency range 6 - 18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C 5H 432 S 14NOH, C 5H 432S 14NOD, and C 5H 434 SNOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ 0 = - 0.023 amu · Å 2 for the C 5H 432 S 14NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O - H) = 0.93(2) Å, R(C - S) = 1.66(2) Å, and angle ∠ (N - O - H) = 105(4)° for the ground state structure. (Figure presented) © 2011 American Chemical Society.
• FRY, H., & KUKOLICH, S. (2011). BEAM MASER MEASUREMENTS OF HDO HYPERFINE-STRUCTURE. JOURNAL OF CHEMICAL PHYSICS, 76(9), 4387-4391.
• Kukolich, S. G., & Sarkozy, L. C. (2011). Design, construction, and testing of a large-cavity, 1-10 GHz Flygare-Balle spectrometer. Review of Scientific Instruments, 82(9).
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  PMID: 21974602;Abstract: A large pulsed-beam, Fourier transform microwave spectrometer employing 48 in. diameter mirrors and 35″ (NHS-35) diffusion pump has been constructed at the University of Arizona. The Fabry-Perot-type cavity, using the large mirrors provides Q-values in the 15 000 to 40 000 range. Test spectra were obtained using transverse and coaxial injection of the pulsed-nozzle molecular beams. The measured molecular resonance linewidths were 8 kHz for the transverse injection and 2 kHz for coaxial molecular beam injection. Good signal to noise ratios were obtained for the test signals. Strong lines for butadiene iron tricarbonyl were seen with a single beam pulse (SN 51). Transitions were measured as low as 900 MHz and some previously unresolved hyperfine structure is now resolved for the butadiene iron tricarbonyl spectra. The spectrometer is operated using a personal computer with LABVIEW programs, with provisions for automatic frequency scanning. The extended, low-frequency range of this spectrometer should make it very useful for making measurements on significantly larger molecules and complexes than have been previously studied. The improved resolution, in the coaxial beam mode, will allow better resolution of hyperfine structure. The large diffusion pump allows a higher beam pulse frequency to compensate for the generally lower sensitivity at lower frequencies. © 2011 American Institute of Physics.
• Kukolich, S. G., & Sarkozy, L. C. (2011). Design, construction, and testing of a large-cavity, 1-10 GHz Flygare-Balle spectrometer. The Review of scientific instruments, 82(9), 094103.
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  A large pulsed-beam, Fourier transform microwave spectrometer employing 48 in. diameter mirrors and 35(") (NHS-35) diffusion pump has been constructed at the University of Arizona. The Fabry-Perot-type cavity, using the large mirrors provides Q-values in the 15,000 to 40,000 range. Test spectra were obtained using transverse and coaxial injection of the pulsed-nozzle molecular beams. The measured molecular resonance linewidths were 8 kHz for the transverse injection and 2 kHz for coaxial molecular beam injection. Good signal to noise ratios were obtained for the test signals. Strong lines for butadiene iron tricarbonyl were seen with a single beam pulse (S/N = 5/1). Transitions were measured as low as 900 MHz and some previously unresolved hyperfine structure is now resolved for the butadiene iron tricarbonyl spectra. The spectrometer is operated using a personal computer with LABVIEW programs, with provisions for automatic frequency scanning. The extended, low-frequency range of this spectrometer should make it very useful for making measurements on significantly larger molecules and complexes than have been previously studied. The improved resolution, in the coaxial beam mode, will allow better resolution of hyperfine structure. The large diffusion pump allows a higher beam pulse frequency to compensate for the generally lower sensitivity at lower frequencies.
• Kukolich, S., Daly, A. M., Douglass, K. O., Sarkozy, L. C., Neill, J. L., Muckle, M. T., Zaleski, D. P., Pate, B. H., & Kukolich, S. G. (2011). Microwave measurements of proton tunneling and structural parameters for the propiolic acid-formic acid dimer. The Journal of chemical physics, 135(15).
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  Microwave spectra of the propiolic acid-formic acid doubly hydrogen bonded complex were measured in the 1 GHz to 21 GHz range using four different Fourier transform spectrometers. Rotational spectra for seven isotopologues were obtained. For the parent isotopologue, a total of 138 a-dipole transitions and 28 b-dipole transitions were measured for which the a-dipole transitions exhibited splittings of a few MHz into pairs of lines and the b-type dipole transitions were split by ~580 MHz. The transitions assigned to this complex were fit to obtain rotational and distortion constants for both tunneling levels: A(0+) = 6005.289(8), B(0+) = 930.553(8), C(0+) = 803.9948(6) MHz, Δ(0+)(J) = 0.075(1), Δ(0+)(JK) = 0.71(1), and δ(0+)(j) = -0.010(1) kHz and A(0-) = 6005.275(8), B(0-) = 930.546(8), C(0-) = 803.9907(5) MHz, Δ(0-)(J) = 0.076(1), Δ(0-)(JK) = 0.70(2), and δ(0-)(j) = -0.008(1) kHz. Double resonance experiments were used on some transitions to verify assignments and to obtain splittings for cases when the b-dipole transitions were difficult to measure. The experimental difference in energy between the two tunneling states is 291.428(5) MHz for proton-proton exchange and 3.35(2) MHz for the deuterium-deuterium exchange. The vibration-rotation coupling constant between the two levels, F(ab), is 120.7(2) MHz for the proton-proton exchange. With one deuterium atom substituted in either of the hydrogen-bonding protons, the tunneling splittings were not observed for a-dipole transitions, supporting the assignment of the splitting to the concerted proton tunneling motion. The spectra were obtained using three Flygare-Balle type spectrometers and one chirped-pulse machine at the University of Virginia. Rotational constants and centrifugal distortion constants were obtained for HCOOH···HOOCCCH, H(13)COOH···HOOCCCH, HCOOD···HOOCCCH, HCOOH···DOOCCCH, HCOOD···DOOCCCH, DCOOH···HOOCCCH, and DCOOD···HOOCCCH. High-level ab initio calculations provided initial rotational constants for the complex, structural parameters, and some details of the proton tunneling potential energy surface. A least squares fit to the isotopic data reveals a planar structure that is slightly asymmetric in the OH distances. The formic OH···O propiolic hydrogen bond length is 1.8 Å and the propiolic OH···O formic hydrogen bond length is 1.6 Å, for the equilibrium configuration. The magnitude of the dipole moment was experimentally determined to be 1.95(3) × 10(-30) C m (0.584(8) D) for the 0(+) states and 1.92(5) × 10(-30) C m (0.576(14) D) for the 0(-) states.
• Kukolich, S., Daly, A. M., Mitchell, E. G., Sanchez, D. A., Block, E., & Kukolich, S. G. (2011). Microwave spectra and gas phase structural parameters for N-hydroxypyridine-2(1H)-thione. The journal of physical chemistry. A, 115(50).
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  The microwave spectrum for N-hydroxypyridine-2(1H)-thione (pyrithione) was measured in the frequency range 6-18 GHz, providing accurate rotational constants and nitrogen quadrupole coupling strengths for three isotopologues, C(5)H(4)(32)S(14)NOH, C(5)H(4)(32)S(14)NOD, and C(5)H(4)(34)S(14)NOH. Pyrithione was found to be in a higher concentration in the gas phase than the other tautomer, 2-mercaptopyridine-N-oxide (MPO). Microwave spectroscopy is best suited to determine which structure predominates in the gas phase. The measured rotational constants were used to accurately determine the coordinates of the substituted atoms and provided sufficient data to determine some of the important structural parameters for pyrithione, the only tautomer observed in the present work. The spectra were obtained using a pulsed-beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of the (14)N nuclear quadrupole hyperfine interactions. Ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The experimental rotational constants for the parent compound are A = 3212.10(1), B = 1609.328(7), and C = 1072.208(6) MHz, yielding the inertial defect Δ(0) = -0.023 amu·Å(2) for the C(5)H(4)(32)S(14)NOH isotopologue. The observed near zero inertial defect clearly indicates a planar structure. The least-squares fit structural analysis yielded the experimental bond lengths R(O-H) = 0.93(2) Å, R(C-S) = 1.66(2) Å, and angle (N-O-H) = 105(4)° for the ground state structure.
• Daly, A. M., Bunker, P. R., & Kukolich, S. G. (2010). Communications: Evidence for proton tunneling from the microwave spectrum of the formic acid-propriolic acid dimer. Journal of Chemical Physics, 132(20).
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  PMID: 20515081;Abstract: The microwave spectrum of the formic acid-propriolic acid dimer was measured in the 5-13 GHz range using a pulsed-beam, Fourier transform spectrometer. 22 a-dipole rotational transitions and 3 b-dipole rovibrational transitions were measured for the normal isotopomer. All of these observed transitions were split into doublets by the effects of the concerted tunneling of the two acid protons. The smaller splittings of 1-1.5 MHz for the a-dipole transitions are due to the differences in rotational constants for the upper and lower tunneling states. The b-dipole transitions are rovibrational (combination) transitions with a change in rotational state and tunneling state and provide direct information on the tunneling splittings since these observed splittings are the sum of the tunneling level splittings for the two rotational states involved in the transition. The b-dipole splittings are 55.16 (0 00 - 111), 58.58 (101 - 212), and 71.24 MHz (202 - 313). No similar splittings were observed when deuterium was substituted for either or both of the hydrogen bonding protons. For the lower tunneling state (ν0+), A=5988.7 (7), B=927.782 (7), and C=803.720 (7) MHz. For the upper tunneling state (ν0-), A=5988 (1), B=927.78 (1), and C=804.06 (1) MHz. Using a simple model with potential function V= ax4 - bx2 the splittings could be reproduced reasonably well with a barrier height of He =3800cm-1. © 2010 American Institute of Physics.
• Daly, A. M., Bunker, P. R., & Kukolich, S. G. (2010). Erratum: Communications: Evidence for proton tunneling from the microwave spectrum of the formic acid: Propriolic acid dimer (J. Chem. Phys. (2010) 132 (201101)). Journal of Chemical Physics, 133(7).
• Daly, A. M., Sargus, B. A., & Kukolich, S. G. (2010). Microwave spectrum and structural parameters for the formamide-formic acid dimer. Journal of Chemical Physics, 133(17).
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  PMID: 21054029;Abstract: The rotational spectra for six isotopologues of the complex formed between formamide and formic acid have been measured using a pulsed-beam Fourier transform microwave spectrometer and analyzed to obtain rotational constants and quadrupole coupling parameters. The rotational constants and quadrupole coupling strengths obtained for H C 12OOH- H214NCOH are A=5889.465 (2), B=2148.7409 (7), 1575.1234(6), eQq aa =1.014 (5), eQqbb =1.99 (1), and eQqcc =-3.00 (1) MHz. Using the 15 rotational constants obtained for the H 13COOH, HCOOD, DCOOH, and H215NCHO isotopologues, key structural parameters were obtained from a least-squares structure fit. Hydrogen bond distances of 1.78 Å for R (O3⋯H) and 1.79 Å for R (H4⋯O1) were obtained. The "best fit" value for the (C-O-H) of formic acid is significantly larger than the monomer value of 106.9° with an optimum value of 121.7(3)°. The complex is nearly planar with inertial defect Δ=-0.158 amu Å2. The formamide proton is moved out of the molecular plane by 15(3)° for the best fit structure. Density functional theory using B3PW91, HCTH407, and TPSS as well as MP2 and CCSD calculations were performed using 6-1++G (d,p) and the results were compared to experimentally determined parameters. © 2010 American Institute of Physics.
• Daly, A. M., Tanjaroon, C., J., A., Liu, S., & Kukolich, S. G. (2010). Microwave spectrum, structural parameters, and quadrupole coupling for 1,2-dihydro-1,2-azaborine. Journal of the American Chemical Society, 132(15), 5501-5506.
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  PMID: 20349985;Abstract: The first microwave spectrum for 1,2-dihydro-1,2-azaborine has been measured in the frequency range 7-18 GHz, providing accurate rotational constants and nitrogen and boron quadrupole coupling strengths for three isotopomers, H6C411B14N, H 6C410B14N, and H5DC 411B14N. The measured rotational constants were used to accurately determine coordinates for the substituted atoms and provide sufficient data to determine most of the important structural parameters for this molecule. The spectra were obtained using a pulsed beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of 14N, 11B, and 10B nuclear quadrupole hyperfine interactions. High-level ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The rotational constants for the parent compound are A = 5657.335(1), B = 5349.2807(5), and C = 2749.1281(4) MHz, yielding the inertial defect δ0 = 0.02 amua å2 for the ground-state structure. The observed near-zero and positive inertial defect clearly indicates that the molecular structure of 1,2-dihydro-1,2-azaborine is planar. The least-squares fit analysis to determine the azaborine ring structure yielded the experimental bond lengths and 2σ errors R(B-N) = 1.45(3) å, R(B-C) = 1.51(1) å, and R(N-C) = 1.37(3) å for the ground-state structure. Interbond angles for the ring were also determined. An extended Townes-Dailey population analysis of the boron and nitrogen quadrupole coupling constants provided the valence p-electron occupancy pc = 0.3e for boron and pc = 1.3e for nitrogen. © 2010 American Chemical Society.
• KUKOLICH, S., & CAMPBELL, E. (2010). MICROWAVE MEASUREMENTS OF BROMINE QUADRUPOLE COUPLING-CONSTANTS AND THE MOLECULAR-STRUCTURE OF XEHBR. CHEMICAL PHYSICS LETTERS, 94(1), 73-76.
• Kukolich, S., Daly, A. M., Bunker, P. R., & Kukolich, S. G. (2010). Communications: Evidence for proton tunneling from the microwave spectrum of the formic acid-propriolic acid dimer. The Journal of chemical physics, 132(20).
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  The microwave spectrum of the formic acid-propriolic acid dimer was measured in the 5-13 GHz range using a pulsed-beam, Fourier transform spectrometer. 22 a-dipole rotational transitions and 3 b-dipole rovibrational transitions were measured for the normal isotopomer. All of these observed transitions were split into doublets by the effects of the concerted tunneling of the two acid protons. The smaller splittings of 1-1.5 MHz for the a-dipole transitions are due to the differences in rotational constants for the upper and lower tunneling states. The b-dipole transitions are rovibrational (combination) transitions with a change in rotational state and tunneling state and provide direct information on the tunneling splittings since these observed splittings are the sum of the tunneling level splittings for the two rotational states involved in the transition. The b-dipole splittings are 55.16(0(00)-1(11)), 58.58(1(01)-2(12)), and 71.24 MHz(2(02)-3(13)). No similar splittings were observed when deuterium was substituted for either or both of the hydrogen bonding protons. For the lower tunneling state (nu(0) (+)), A=5988.7(7), B=927.782(7), and C=803.720(7) MHz. For the upper tunneling state (nu(0) (-)), A=5988(1), B=927.78(1), and C=804.06(1) MHz. Using a simple model with potential function V=ax(4)-bx(2) the splittings could be reproduced reasonably well with a barrier height of H(e)=3800 cm(-1).
• Kukolich, S., Daly, A. M., Sargus, B. A., & Kukolich, S. G. (2010). Microwave spectrum and structural parameters for the formamide-formic acid dimer. The Journal of chemical physics, 133(17).
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  The rotational spectra for six isotopologues of the complex formed between formamide and formic acid have been measured using a pulsed-beam Fourier transform microwave spectrometer and analyzed to obtain rotational constants and quadrupole coupling parameters. The rotational constants and quadrupole coupling strengths obtained for H  (12)COOH-H(2)  (14)NCOH are A = 5889.465(2), B = 2148.7409(7), 1575.1234(6), eQq(aa) = 1.014(5), eQq(bb) = 1.99(1), and eQq(cc) = -3.00(1) MHz. Using the 15 rotational constants obtained for the H  (13)COOH, HCOOD, DCOOH, and H(2)  (15)NCHO isotopologues, key structural parameters were obtained from a least-squares structure fit. Hydrogen bond distances of 1.78 Å for R(O3⋯H1) and 1.79 Å for R(H4⋯O1) were obtained. The "best fit" value for the angle(C-O-H) of formic acid is significantly larger than the monomer value of 106.9° with an optimum value of 121.7(3)°. The complex is nearly planar with inertial defect Δ = -0.158 amu  Å(2). The formamide proton is moved out of the molecular plane by 15(3)° for the best fit structure. Density functional theory using B3PW91, HCTH407, and TPSS as well as MP2 and CCSD calculations were performed using 6-311++G(d,p) and the results were compared to experimentally determined parameters.
• Kukolich, S., Daly, A. M., Tanjaroon, C., Marwitz, A. J., Liu, S., & Kukolich, S. G. (2010). Microwave spectrum, structural parameters, and quadrupole coupling for 1,2-dihydro-1,2-azaborine. Journal of the American Chemical Society, 132(15).
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  The first microwave spectrum for 1,2-dihydro-1,2-azaborine has been measured in the frequency range 7-18 GHz, providing accurate rotational constants and nitrogen and boron quadrupole coupling strengths for three isotopomers, H(6)C(4)(11)B(14)N, H(6)C(4)(10)B(14)N, and H(5)DC(4)(11)B(14)N. The measured rotational constants were used to accurately determine coordinates for the substituted atoms and provide sufficient data to determine most of the important structural parameters for this molecule. The spectra were obtained using a pulsed beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of (14)N, (11)B, and (10)B nuclear quadrupole hyperfine interactions. High-level ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The rotational constants for the parent compound are A = 5657.335(1), B = 5349.2807(5), and C = 2749.1281(4) MHz, yielding the inertial defect Delta(0) = 0.02 amu x A(2) for the ground-state structure. The observed near-zero and positive inertial defect clearly indicates that the molecular structure of 1,2-dihydro-1,2-azaborine is planar. The least-squares fit analysis to determine the azaborine ring structure yielded the experimental bond lengths and 2sigma errors R(B-N) = 1.45(3) A, R(B-C) = 1.51(1) A, and R(N-C) = 1.37(3) A for the ground-state structure. Interbond angles for the ring were also determined. An extended Townes-Dailey population analysis of the boron and nitrogen quadrupole coupling constants provided the valence p-electron occupancy p(c) = 0.3e for boron and p(c) = 1.3e for nitrogen.
• ROEHRIG, M., & KUKOLICH, S. (2010). THE MICROWAVE-SPECTRUM AND STRUCTURE FOR THE HCCH-CO COMPLEX. CHEMICAL PHYSICS LETTERS, 188(3-4), 232-236.
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  Rotational transitions were measured for five isotopomers of HCCH-CO using a Flygare-Balle type microwave spectrometer. The observed spectrum is consistent with a linear, hydrogen-bonded HCCH-CO structure. Measured rotational constants in MHz, are B = 1397.370(1) for HCCH-CO, 1394.963(1) for HCCD-CO, 1385.142(1) for HCCH-(CO)-C-13, 1331.23(1) for DCCH-CO and 1329.684(2) for DCCD-CO. The measured rotational constants were fit to obtain a center-of-mass separation for HCCH-CO of R(c.m.)* = 5.018 (7) angstrom. Distortion constants were obtained and analyzed to obtain a force constant and estimate the dissociation energy.
• Kukolich, S., Tanjaroon, C., & Kukolich, S. G. (2009). Measurements of the rotational spectra of phenol and 2-pyrone and computational studies of the H-bonded phenol-pyrone dimer. The journal of physical chemistry. A, 113(32).
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  Rotational spectra for the a-type transitions of phenol and a-type and b-type transitions of 2-pyrone in the ground vibrational states were measured using pulsed beam Fourier transform (PBFT) microwave spectroscopy. From the observed a-type spectrum of phenol, which exhibited no complicated tunneling doublet splittings, we obtained the following rotational constants: A0 = 5650.494(26), B0 = 2619.2323(7), C0 = 1789.8520(7) MHz. For 2-pyrone, the following rotational constants were obtained: A0 = 5677.6356(10), B0 = 2882.2458(11), C0 = 1912.13275(94) MHz. The centrifugal distortion constant, DeltaJ, for these molecules is less than 0.2 kHz, in good agreement with our predicted, theoretical Delta(J) values. Combined spectral fits using data from this work and previous data provided accurate information on the rotational and centrifugal distortion constants of these molecules. From the measured rotational constants we obtained the following inertial defects (Delta): Delta(2-pyrone) = -0.053 and Delta(phenol) = -0.031 amu A2. The observed negative inertial defect for these planar molecules (normally a small positive value for planar molecules) suggests that the out-of-plane vibrational potential due to the attached OH and O is highly anharmonic. From the measured inertial defect, we calculated the low frequency out-of-plane vibration to be approximately 110 cm(-1). Quantum chemical calculations were performed in combination with the experiments to determine the molecular and spectroscopic properties of phenol, 2-pyrone and the H-bonded, phenol-pyrone dimer. A well-defined theoretical structure was obtained for the phenol-pyrone dimer from the calculations with electron correlation. Structure optimization calculations using Møller-Plesset perturbation theory predicted a stable bent dimer structure with relatively strong interaction energy in the 28-32 kJ mol(-1) range. This novel, phenol-pyrone dimer forms a single O...HO hydrogen bond with length about 1.87-1.93 A, and is further stabilized by pi-pi and CH-pi interactions. Density functional theory (DFT) calculations predicted that a planar nontransition state structure would be stable, but failed to predict a stable bent structure. Experimental searches for the rotational spectrum of phenol-pyrone stable were conducted in the 4-8 GHz range, but no transitions were detected in this study. A number of microwave transitions for the phenol-phenol dimer were detected in this study and used to estimate rotational constants.
• Kukolich, S., Tanjaroon, C., Daly, A., Marwitz, A. J., Liu, S., & Kukolich, S. G. (2009). Microwave measurements and ab initio calculations of structural and electronic properties of N-Et-1,2-azaborine. The Journal of chemical physics, 131(22).
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  Rotational transitions for N-Et-1,2-azaborine were measured in the 5-13 GHz range using a Flygare-Balle type Fourier transform spectrometer system. Twelve distinct rotational transitions with over 130 resolved hyperfine components, which included a-dipole and b-dipole transitions, were measured and analyzed to obtain rotational constants and (11)B and (14)N nuclear quadrupole coupling constants in the principal rotational axis system. Rotational constants obtained are A=4477.987(4), B=1490.5083(7), and C=1230.6728(6) MHz. The quadrupole coupling constants for (11)B are eQq(aa)=-1.82(1), (eQq(bb)-eQq(cc))=-3.398(4) MHz, and for (14)N, eQq(aa)=1.25(1), (eQq(bb)-eQq(cc))=0.662(4) MHz. Quantum electronic structure calculations predict a ground-state structure with the ethyl group perpendicular to the azaborine plane and rotational constants in very good agreement with the measured structure and rotational constants. The theoretical conformational analysis of the ethyl group rotation around the N[Single Bond]C bond in relation to the heterocyclic ring yielded an asymmetric torsional potential energy surface with barrier heights of about 900 and 1350 cm(-1) for the N-Et-1,2-azaborine. Results of the measurements and calculations indicate that the basic molecular structure of N-Et-1,2-azaborine is similar to ethylbenzene. Electrostatic potential calculations qualitatively show that pi-electron density is somewhat delocalized around the 1,2-azaborine ring.
• Tanjaroon, C., & Kukolich, S. G. (2009). Measurements of the rotational spectra of phenol and 2-pyrone and computational studies of the H-bonded phenol-pyrone dimer. Journal of Physical Chemistry A, 113(32), 9185-9192.
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  PMID: 19610662;Abstract: Rotational spectra for the a-type transitions of phenol and a-type and b-type transitions of 2-pyrone in the ground vibrational states were measured using pulsed beam Fourier transform (PBFT) microwave spectroscopy. From the observed a-type spectrum of phenol, which exhibited no complicated tunneling doublet splittings, we obtained the following rotational constants: A 0 = 5650.494(26), B0 = 2619.2323(7), C0 = 1789.8520(7) MHz. For 2-pyrone, the following rotational constants were obtained: A0 = 5677.6356(10), B0 = 2882.2458(11), C 0 = 1912.13275(94) MHz. The centrifugal distortion constant, Δj, for these molecules is less than 0.2 kHz, in good agreement with our predicted, theoretical Δj values. Combined spectral fits using data from this work and previous data provided accurate information on the rotational and centrifugal distortion constants of these molecules. From the measured rotational constants we obtained the following inertial defects (Δ): Δ(2-pyrone) = -0.053 and Δ(phenol) = -0.031 amu Å2. The observed negative inertial defect for these planar molecules (normally a small positive value for planar molecules) suggests that the out-of-plane vibrational potential due to the attached OH and O is highly anharmonic. From the measured inertial defect, we calculated the low frequency out-of-plane vibration to be approximately 110 cm-1. Quantum chemical calculations were performed in combination with the experiments to determine the molecular and spectroscopic properties of phenol, 2-pyrone and the H - bonded, phenol-pyrone dimer. A well-defined theoretical structure was obtained for the phenol-pyrone dimer from the calculations with electron correlation. Structure optimization calculations using Møller-Plesset perturbation theory predicted a stable bent dimer structure with relatively strong interaction energy in the 28-32 kJ mol-1 range. This novel, phenol-pyrone dimer forms a single O'-HO hydrogen bond with length about 1.87-1.93 Å, and is further stabilized by π-π and CH - π interactions. Density functional theory (DFT) calculations predicted that a planar nontransition state structure would be stable, but failed to predict a stable bent structure. Experimental searches for the rotational spectrum of phenol-pyrone stable were conducted in the 4-8 GHz range, but no transitions were detected in this study. A number of microwave transitions for the phenol-phenol dimer were detected in this study and used to estimate rotational constants. © 2009 American Chemical Society.
• Tanjaroon, C., Daly, A., J., A., Liu, S., & Kukolich, S. (2009). Microwave measurements and ab initio calculations of structural and electronic properties of N -Et-1,2-azaborine. Journal of Chemical Physics, 131(22).
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  PMID: 20001041;Abstract: Rotational transitions for N -Et-1,2-azaborine were measured in the 5-13 GHz range using a Flygare-Balle type Fourier transform spectrometer system. Twelve distinct rotational transitions with over 130 resolved hyperfine components, which included a-dipole and b-dipole transitions, were measured and analyzed to obtain rotational constants and 11B and 14N nuclear quadrupole coupling constants in the principal rotational axis system. Rotational constants obtained are A=4477.987(4), B=1490.5083(7), and C=1230.6728(6) MHz. The quadrupole coupling constants for 11B are eQqaa=-1.82(1), (eQqbb-eQqcc)=-3.398 (4) MHz, and for 14N, eQqaa=1.25(1), (eQqbb-eQq cc)=0.662(4) MHz. Quantum electronic structure calculations predict a ground-state structure with the ethyl group perpendicular to the azaborine plane and rotational constants in very good agreement with the measured structure and rotational constants. The theoretical conformational analysis of the ethyl group rotation around the N-C bond in relation to the heterocyclic ring yielded an asymmetric torsional potential energy surface with barrier heights of about 900 and 1350 cm-1 for the N-Et-1,2-zaborine. Results of the measurements and calculations indicate that the basic molecular structure of N-Et-1,2-azaborine is similar to ethylbenzene. Electrostatic potential calculations qualitatively show that π-electron density is somewhat delocalized around the 1,2-azaborine ring. © 2009 American Institute of Physics.
• Kukolich, S., Tanjaroon, C., Daly, A. M., & Kukolich, S. G. (2008). The rotational spectrum and structure for the argon-cyclopentadienyl thallium van der Waals complex: experimental and computational studies of noncovalent bonding in an organometallic pi-complex. The Journal of chemical physics, 129(5).
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  The rotational spectrum of a noble gas-organometallic complex was measured using a pulse molecular beam Fourier transform microwave spectrometer. Rotational transitions for the neutral argon-cyclopentadienyl thallium weakly bound complex were measured in the 4-9 GHz range. Analysis of the spectrum showed that the complex is a prolate symmetric-top rotor with C(5V) symmetry. The experimentally determined molecular parameters for Ar-C(5)H(5) (205)Tl are B=372.4479(3) MHz, D(J)=0.123(2) kHz, and D(JK)=0.45(2) kHz. For Ar-C(5)H(5) (203)Tl, B=373.3478(5) MHz, D(J)=0.113(3) kHz, and D(JK)=0.37(3) kHz. Using a pseudodiatomic model with Lennard-Jones potential yields an approximate binding energy of 339 cm(-1). The argon atom is located on the a-axis of the C(5)H(5)Tl monomer, directly opposite from the thallium metal atom. The measured separation distance between argon and the cyclopentadienyl ring is R=3.56 A. The overall size of the cluster is about 6 A, measuring from argon to thallium. Relatively small D(J) and D(JK) centrifugal distortion constants were observed for the complex, indicating that the structure of Ar-C(5)H(5)Tl is somewhat rigid. MP2 calculations were used to investigate the possible structures and binding energies of the argon-cyclopentadienyl thallium complex. Calculated, counterpoise corrected binding energies are evaluated at R=3.56 A for Ar-C(5)H(5)Tl range from 334 to 418 cm(-1). The experimental binding energy epsilon=339 cm(-1) for Ar-C(5)H(5)Tl falls within this range. The higher-level MP2/aug-cc-pVTZ-PP (thallium)/aug-cc-pVTZ(Ar, C, H) calculation with variable R yielded R(e)=3.46 A and binding energy of 535 cm(-1). Our estimated binding energy for argon-cyclopentadienyl thallium is very similar to the binding energy of argon-benzene. Calculations for the new van der Waals complexes, Ar(C(5)H(5)Tl)(2) and (C(5)H(5)Tl)(2), have been obtained, providing further information on the structures and bonding properties of previously observed cyclopentadienyl thallium polymer chains. The calculated intermolecular distance R(Tl-Cp)=3.05 A for the (CpTl)(2) chain subunit (Cp is cyclopentadienyl, C(5)H(5)) is slightly longer than the measured x-ray value R(M-Cp)(M=Tl)=2.75 A. The x-ray distance R(Tl-Tl)=5.5 A for the chain structure is almost identical to the calculated R(Tl-Tl)=5.51 A for the (C(5)H(5)Tl)(2) dimer.
• Tanjaroon, C., Daly, A. M., & Kukolich, S. G. (2008). The rotational spectrum and structure for the argon-cyclopentadienyl thallium van der Waals complex: Experimental and computational studies of noncovalent bonding in an organometallic π -complex. Journal of Chemical Physics, 129(5).
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  PMID: 18698898;Abstract: The rotational spectrum of a noble gas-organometallic complex was measured using a pulse molecular beam Fourier transform microwave spectrometer. Rotational transitions for the neutral argon-cyclopentadienyl thallium weakly bound complex were measured in the 4-9 GHz range. Analysis of the spectrum showed that the complex is a prolate symmetric-top rotor with C5V symmetry. The experimentally determined molecular parameters for Ar- C 5H5205Tl are B=372.4479 (3) MHz, D J=0.123 (2) kHz, and DJK =0.45 (2) kHz. For Ar-C 5H5 T 203 l, B=373.3478 (5) MHz, DJ=0.113 (3) kHz, and DJK=0.37 (3) kHz. Using a pseudodiatomic model with Lennard-Jones potential yields an approximate binding energy of 339 cm -1. The argon atom is located on the a -axis of the C 5H5Tl monomer, directly opposite from the thallium metal atom. The measured separation distance between argon and the cyclopentadienyl ring is R=3.56 Å. The overall size of the cluster is about 6 Å, measuring from argon to thallium. Relatively small DJ and DJK centrifugal distortion constants were observed for the complex, indicating that the structure of Ar- C5H5Tl is somewhat rigid. MP2 calculations were used to investigate the possible structures and binding energies of the argon-cyclopentadienyl thallium complex. Calculated, counterpoise corrected binding energies are evaluated at R=3.56 Å for Ar- C5H5Tl range from 334 to 418 cm-1. The experimental binding energy ε=339 cm-1 for Ar-C 5H5Tl falls within this range. The higher-level MP2/aug-cc-pVTZ-PP (thallium)/aug-cc-pVTZ(Ar, C, H) calculation with variable R yielded Re =3.46 Å and binding energy of 535 cm-1. Our estimated binding energy for argon-cyclopentadienyl thallium is very similar to the binding energy of argon-benzene. Calculations for the new van der Waals complexes, Ar (C5H5Tl)2 and (C 5H5Tl)2, have been obtained, providing further information on the structures and bonding properties of previously observed cyclopentadienyl thallium polymer chains. The calculated intermolecular distance RTl-Cp =3.05 Å for the (CpTl)2 chain subunit (Cp is cyclopentadienyl, C5H5) is slightly longer than the measured x-ray value RM-Cp (M=Tl) =2.75 Å. The x-ray distance RTl-Tl =5.5 Å for the chain structure is almost identical to the calculated R Tl-Tl =5.51 Å for the (C5H5Tl) 2 dimer. © 2008 American Institute of Physics.
• Tanjaroon, C., Sebonia, M., & Kukolich, S. G. (2008). The rotational spectrum of the cyclopentadienylallylnickel complex. Chemical Physics, 344(3), 209-212.
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  Abstract: The rotational spectrum of cyclopentadienylallylnickel, C3H5NiC5H5, has been studied using a pulsed molecular beam Fourier transform microwave spectrometer. Twelve a-type transitions were analyzed to obtain rotational and centrifugal distortion constants for the parent C3H558NiC5H5 complex. The measured rotational constant A = 3107.603(93) MHz is about 160.0 MHz larger than the predicted DFT value, providing evidence for possible fluxional motion in the complex. The large distortion constants, on the order of 100 kHz, provide further evidence for fluxional motion. The experimental constants B = 1302.38(22) and C = 1276.40(15) MHz are in good agreement with the DFT calculated values and confirm the η3-bonding of the allyl ligand to the Ni-C5H5 moiety. DFT calculations provide a V5 barrier for internal rotation about the Ni-C5H5 axis of 53 cm-1, with the lowest energy conformation having the central allyl c-atom eclipsed with respect to two C5H5 carbon atoms. Several additional rotational lines, possibly those of an exited torsional state, were observed but not assigned. © 2008 Elsevier B.V. All rights reserved.
• Daly, A. M., Daly, A. M., Bunker, P. R., Bunker, P. R., Kukolich, S. G., & Kukolich, S. G. (2007). Communications: Evidence for proton tunneling from the microwave spectrum of the formic acid-propriolic acid dimer. JOURNAL OF CHEMICAL PHYSICS, 132(20).
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  The microwave spectrum of the formic acid-propriolic acid dimer was measured in the 5-13 GHz range using a pulsed-beam, Fourier transform spectrometer. 22 a-dipole rotational transitions and 3 b-dipole rovibrational transitions were measured for the normal isotopomer. All of these observed transitions were split into doublets by the effects of the concerted tunneling of the two acid protons. The smaller splittings of 1-1.5 MHz for the a-dipole transitions are due to the differences in rotational constants for the upper and lower tunneling states. The b-dipole transitions are rovibrational (combination) transitions with a change in rotational state and tunneling state and provide direct information on the tunneling splittings since these observed splittings are the sum of the tunneling level splittings for the two rotational states involved in the transition. The b-dipole splittings are 55.16(0(00)-1(11)), 58.58(1(01)-2(12)), and 71.24 MHz(2(02)-3(13)). No similar splittings were observed when deuterium was substituted for either or both of the hydrogen bonding protons. For the lower tunneling state (nu(0)+), A=5988.7(7), B=927.782(7), and C=803.720(7) MHz. For the upper tunneling state (nu(0)-), A=5988(1), B=927.78(1), and C=804.06(1) MHz. Using a simple model with potential function V=ax(4)-bx(2) the splittings could be reproduced reasonably well with a barrier height of H(e)=3800 cm(-1). (C) 2010 American Institute of Physics. [doi: 10.1063/1.3443508]
• Karunatilaka, C., Subramanian, R., Pedroza, D., Idar, D. J., & Kukolich, S. G. (2007). High-resolution infrared spectrum of the v ₁ band of η ⁵-C ₅H ₅NiNO. Journal of Physical Chemistry A, 111(28), 6191-6196.
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  PMID: 17585744;Abstract: Gas-phase rotational constants and distortion constants have been determined for the v 1 (v = 1) excited vibrational state of cyclopentadienylnickel nitrosyl (C 5H 5NiNO) using a high-resolution Fourier transform spectrometer system at Kitt Peak, Arizona. The rotationally resolved lines have been measured for the C-H symmetric stretch vibration (v 1 = 3110 cm -1). In the present analysis, over 150 lines have been assigned and fitted using a rigid-rotor Hamiltonian with centrifugal distortion. The vibrational band center, excited-state rotational constants, and distortion constants derived from the measured spectrum for this prolate symmetric-top molecule are v o = 3110.4129(4) cm -1, A′ = 0.14328(8) cm -1, B′ = C′ = 0.041285(1) cm -1, D J′ = 0.078(1) kHz, D JK′ = 2.23(4) kHz, and D K′ = -2.63(2) kHz, respectively. Several different combination differences, with a common upper state, were calculated for different K stacks for the observed spectra, and the consistency of the lower state rotational constants obtained provided further support for the current assignment. The ground-state rotational constant (B″) derived from this combination differences analysis agrees with the previously obtained Fourier transform microwave value to within 0.15%. However, ground-state rotational constants, A″ and B″, have been fixed in the present analysis to avoid correlation effects and to get more accurate results. The new measured parameters are compared with the previously obtained results from Fourier transform microwave and infrared spectroscopy measurements. The C-H vibration stretching frequency and rotational constants were calculated using density functional theory calculations, and these were quite helpful in resolving ambiguities in the fitting procedure and for initial assignments of measured lines. © 2007 American Chemical Society.
• Karunatilaka, C., Tackett, B. S., Washington, J., & Kukolich, S. G. (2007). Structure of tetracarbonylethyleneosmium: Ethylene structure changes upon complex formation. Journal of the American Chemical Society, 129(34), 10522-10530.
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  PMID: 17676739;Abstract: Rotational spectra of seven isotopomers of tetracarbonylethyleneosmium, Os(CO)4(η2-C2H4), were measured in the 4-12 GHz range using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer system. Olefin-transition metal complexes of this type occur extensively in recent organic syntheses and serve as important models for transition states in the metal-mediated transformations of alkenes. Three osmium (192Os, 190Os, and 188Os) and three unique 13C isotopomers (13C in ethylene, axial, and equatorial positions) were observed in natural abundance. Additional spectra were measured for a perdeuterated sample, Os(CO)4(η2-C 2D4). The measured rotational constants for the main osmium isotopomer (192Os) are A = 929.3256(6), B = 755.1707(3), and C = 752.7446(3) MHz, indicating a near-prolate asymmetric top molecule. The ∼140 assigned b-type transitions were fit using a Watson S-reduced Hamiltonian including A, B, C, and five centrifugal distortion constants. A near-complete r0 gas-phase structure has been determined from a least-squares structural fit using eight adjustable structural parameters to fit the 21 measured rotational constants. Changes in the structure of ethylene on coordination to Os(CO)4 are large and well-determined. For the complex, the experimental ethylene C-C bond length is 1.432(5) Å, which falls between the free ethylene value of 1.3391 (13) Å and the ethane value of 1.534(2) Å. The angle between the plane of the CH2 group and the extended ethylene C-C bond (Zout-of-plane) is 26.0(3)°, indicating that this complex is better described as a metallacyclopropane than as a π-bonded olefin-metal complex. The Os-C-C-H dihedral angle is 106.7(2)°, indicating that the ethylene carbon atoms have near sp 3 character in the complex. Kraitchman analysis of the available rotational constants gave principal axis coordinates for the carbon and hydrogen atoms in excellent agreement with the least-squares fit results. The new results on this osmium complex are compared with earlier work on the similar complex, tetracarbonylethyleneiron (Fe(CO)4(η2-C 2H4)). The ethylene structural changes upon coordination to the metal are found to be larger for the ethylene-osmium complex than for the analogous ethylene-iron complex, consistent with the expected greater π donation for the osmium atom. © 2007 American Chemical Society.
• Kukolich, S., Karunatilaka, C., Subramanian, R., Pedroza, D., Idar, D. J., & Kukolich, S. G. (2007). High-resolution infrared spectrum of the nu1 Ba nd of eta5-C5H5NiNO. The journal of physical chemistry. A, 111(28).
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  Gas-phase rotational constants and distortion constants have been determined for the nu1 (v=1) excited vibrational state of cyclopentadienylnickel nitrosyl (C5H5NiNO) using a high-resolution Fourier transform spectrometer system at Kitt Peak, Arizona. The rotationally resolved lines have been measured for the C-H symmetric stretch vibration (nu1=3110 cm(-1)). In the present analysis, over 150 lines have been assigned and fitted using a rigid-rotor Hamiltonian with centrifugal distortion. The vibrational band center, excited-state rotational constants, and distortion constants derived from the measured spectrum for this prolate symmetric-top molecule are nuo=3110.4129(4) cm(-1), A'=0.14328(8) cm(-1), B'=C'=0.041285(1) cm(-1), DJ'=0.078(1) kHz, DJK'=2.23(4) kHz, and DK'=-2.63(2) kHz, respectively. Several different combination differences, with a common upper state, were calculated for different K stacks for the observed spectra, and the consistency of the lower state rotational constants obtained provided further support for the current assignment. The ground-state rotational constant (B'') derived from this combination differences analysis agrees with the previously obtained Fourier transform microwave value to within 0.15%. However, ground-state rotational constants, A'' and B'', have been fixed in the present analysis to avoid correlation effects and to get more accurate results. The new measured parameters are compared with the previously obtained results from Fourier transform microwave and infrared spectroscopy measurements. The C-H vibration stretching frequency and rotational constants were calculated using density functional theory calculations, and these were quite helpful in resolving ambiguities in the fitting procedure and for initial assignments of measured lines.
• Kukolich, S., Karunatilaka, C., Tackett, B. S., Washington, J., & Kukolich, S. G. (2007). Structure of tetracarbonylethyleneosmium: ethylene structure changes upon complex formation. Journal of the American Chemical Society, 129(34).
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  Rotational spectra of seven isotopomers of tetracarbonylethyleneosmium, Os(CO)4(eta2-C2H4), were measured in the 4-12 GHz range using a Flygare-Balle-type pulsed-beam Fourier transform microwave spectrometer system. Olefin-transition metal complexes of this type occur extensively in recent organic syntheses and serve as important models for transition states in the metal-mediated transformations of alkenes. Three osmium ((192)Os, (190)Os, and (188)Os) and three unique 13C isotopomers (13C in ethylene, axial, and equatorial positions) were observed in natural abundance. Additional spectra were measured for a perdeuterated sample, Os(CO)4(eta2-C2D4). The measured rotational constants for the main osmium isotopomer ((192)Os) are A = 929.3256(6), B = 755.1707(3), and C = 752.7446(3) MHz, indicating a near-prolate asymmetric top molecule. The approximately 140 assigned b-type transitions were fit using a Watson S-reduced Hamiltonian including A, B, C, and five centrifugal distortion constants. A near-complete r0 gas-phase structure has been determined from a least-squares structural fit using eight adjustable structural parameters to fit the 21 measured rotational constants. Changes in the structure of ethylene on coordination to Os(CO)4 are large and well-determined. For the complex, the experimental ethylene C-C bond length is 1.432(5) A, which falls between the free ethylene value of 1.3391(13) A and the ethane value of 1.534(2) A. The angle between the plane of the CH2 group and the extended ethylene C-C bond ( angleout-of-plane) is 26.0(3) degrees , indicating that this complex is better described as a metallacyclopropane than as a pi-bonded olefin-metal complex. The Os-C-C-H dihedral angle is 106.7(2) degrees , indicating that the ethylene carbon atoms have near sp3 character in the complex. Kraitchman analysis of the available rotational constants gave principal axis coordinates for the carbon and hydrogen atoms in excellent agreement with the least-squares fit results. The new results on this osmium complex are compared with earlier work on the similar complex, tetracarbonylethyleneiron (Fe(CO)4(eta2-C2H4)). The ethylene structural changes upon coordination to the metal are found to be larger for the ethylene-osmium complex than for the analogous ethylene-iron complex, consistent with the expected greater pi donation for the osmium atom.
• Tackett, B. S., Karunatilaka, C., Daly, A. M., & Kukolich, S. G. (2007). Microwave spectra and gas-phase structural parameters of bis(η⁵-cyclopentadienyl)tungsten dihydride. Organometallics, 26(8), 2070-2076.
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  Abstract: Microwave spectra for 11 isotopomers of bis(η5- cyclopentadienyl)tungsten dihydride ((C5H5) 2WH2) were recorded in the 5-14 GHz region using a Flygare-Balle-type pulsed beam spectrometer. Spectra arising from four tungsten isotopomers of both the (C5H5)2WH2 and (C5H5)2WHD species and three W isotopomers for the (C5H5)2WD2 complex have been measured. The ∼250 b-type transition frequencies assigned for these near-prolate asymmetric top molecules were accurately described (σfit; = 2-4 kHz) using the rotational parameters A, B, and C and one centrifugal distortion constant, ΔJ. The small value obtained for ΔJ indicates a fairly rigid structure. From a least-squares fit using the resulting 33 rotational constants to obtain the molecular structure, we were able to determine the W-H bond length, r(W-H) = 1.703(2) Å, the H-W-H bond angle, ∠(H-W-H) = 78.0(12)°, the W-Cp centroid distance, r(W-Cp) = 1.940(8) Å, the angle made by the Cp centroids with tungsten, ∠(Cp-W-Cp) = 155(2)°, and the average C-C bond length, r(C-C) = 1.429(8) Å. The hydrogen atom separation is r(H-H) = 2.14(2) Å, indicating that this is clearly a "classical dihydride" rather than an "η2-dihydrogen" complex. The WH2 moiety parameters determined from Kraitchman's equations (r(W-H) = 1.682(2) Å, ∠(H-W-H) = 78.6(2), r(H-H) = 2.130(2) Å) agree well with the least-squares' results. Furthermore, the re parameters obtained from DFT calculations agree well with the experimental r0 structural parameters. To our knowledge, this work marks the first microwave study of a bent-metallocene complex. The present measurements were made with a pulsed-beam Fourier transform spectrometer employing a homodyne-type detection system, and this configuration is described. This homodyne system greatly simplifies the microwave circuit, with no apparent loss in sensitivity. © 2007 American Chemical Society.
• Groner, P., & Kukolich, S. G. (2006). Equilibrium structure of gas phase o-benzyne. Journal of Molecular Structure, 780-781(SPEC. ISS.), 178-181.
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  Abstract: An equilibrium structure has been derived for o-benzyne from experimental rotational constants of seven isotopomers and vibration-rotation constants calculated from MP2 (full)/6-31G(d) quadratic and cubic force fields. In the case of benzene, this method yields results that are in excellent agreement with those obtained from high quality ab initio force fields. The ab initio-calculated vibrational averaging corrections were applied to the measured A0, B0 and C0 rotational constants and the resulting experimental, near-equilibrium, rotational constants were used in a least squares fit to determine the approximate equilibrium structural parameters. The C-C bond lengths for this equilibrium structure of o-benzyne are, beginning with the formal triple bond (C1-C2): 1.255, 1.383, 1.403 and 1.405 Å. The bond angles obtained are in good agreement with most of the recent ab initio predictions. © 2005 Elsevier B.V. All rights reserved.
• Keck, K. S., Tanjaroon, C., & Kukolich, S. G. (2005). Rotational and hyperfine spectra for a sandwich titanium complex, C ₅H₅TiC₇H₇. Journal of Molecular Spectroscopy, 232(1), 55-60.
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  Abstract: Microwave spectroscopy measurements and density functional theory calculations are reported for the cyclopentadienyl cycloheptatrienyl titanium complex, C5H5TiC7H7. Rotational transition frequencies for this symmetric-top complex were measured in the 4-13 GHz range using a Flygare-Balle-type pulsed beam spectrometer. The spectroscopic constants obtained for the normal C5H548TiC7H7 isotopomer are B = 771.78907(38), DJ = 0.0000295(41), and DJK = 0.001584(73) MHz. The quadrupole hyperfine splittings for C5H547TiC7H7 were clearly observed and the measured constants are B = 771.79024(32) MHz, DJ = 0.0000395(33), D JK = 0.001646(24), and eQqaa = 8.193(40) MHz. Analysis of the experimental and theoretical rotational constants indicates that the η7-C7H7Ti and η5-C 5H5Ti bond lengths in the gas phase are about 0.02 Å longer than those reported for the solid-state X-ray structure. The calculated Ti-C bond lengths are shorter for the C7H7 ligand (r(Ti-C) = 2.21 Å) than for the C5H5 ligand (r(Ti-C) = 2.34 Å), and the C7H7 H atoms are displaced 0.15 Å out of the C7 plane, toward the Ti atom. © 2005 Elsevier Inc. All rights reserved.
• Kukolich, S., Subramanian, R., Karunatilaka, C., Keck, K. S., & Kukolich, S. G. (2005). The gas phase structure of ethynylferrocene using microwave spectroscopy. Inorganic chemistry, 44(9).
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  Gas phase structural parameters for ethynylferrocene have been determined using microwave spectroscopy. Rotational transitions due to a- and b-type dipole moments were measured. Twenty four rotational constants have been determined by fitting the measured transitions of various isotopomers using a rigid rotor Hamiltonian with centrifugal distortion constants. Least-squares fits to determine structural parameters and Kraitchman analyses have been used to determine the gas phase structural parameters and the atomic coordinates from the rotational constants. The distance between the Fe atom and the C atoms of the cyclopentadienyl rings is r(Fe-C1) = 2.049(5) A, and the distance between the carbon atoms of the cyclopentadienyl ring is r(C-C) = 1.432(2) A. The ethynyl group is bent away from the Fe atom and out of the plane of the carbon atoms in the adjacent cyclopentadienyl ring by 2.75(6) degrees. Structural parameters were also obtained from DFT calculations and Kraitchman analyses, and the results are compared. Analysis of fit results for 13C isotopic substitution data indicates that the carbon atoms of the two cyclopentadienyl rings are in an eclipsed conformation in the ground vibrational state. Trends in microwave experimental values for the distance from the Fe atom to the center of the cyclopentadienyl ring for a series of substituted ferrocenes have been analyzed. This analysis provides an estimate of the gas phase distance from the Fe atom to the centers of the cyclopentadienyl rings for ferrocene of 1.65(1) A.
• Kukolich, S., Subramanian, R., Karunatilaka, C., Schock, R. O., Drouin, B. J., Cassak, P. A., & Kukolich, S. G. (2005). Determination of structural parameters for ferrocenecarboxaldehyde using Fourier transform microwave spectroscopy. The Journal of chemical physics, 123(5).
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  Gas-phase structural parameters for ferrocenecarboxaldehyde have been determined using Fourier transform microwave spectroscopy. Rotational transitions due to a-, b-, and c-type dipole moments were measured. Eighteen rotational constants were determined by fitting the measured transitions of various isotopomers using a rigid rotor Hamiltonian with centrifugal distortion constants. Least-squares fit and Kraitchman analyses have been used to determine the gas-phase structural parameters and the atomic coordinates of the molecule using the rotational constants for various isotopomers. Structural parameters determined from the least-squares fit are the Fe-C bond lengths to the cyclopentadienyl rings, r(Fe-C)=2.047(4) A, and the distance between the carbon atoms of the cyclopentadienyl rings, r(C-C)=1.430(2) A and r(C1-C1')=1.46(1) A of ring carbon and aldehyde carbon atom. Structural parameters were also obtained using density-functional theory calculations, and these were quite helpful in resolving ambiguities in the structural fit analysis, and providing some fixed parameters for the structural analysis. The results of the least squares and the calculations indicate that the carbon atoms of the Cp groups for ferrocenecarboxaldehyde are in an eclipsed conformation in the ground vibrational state.
• Subramanian, R., Karunatilaka, C., Schock, R. O., Drouin, B. J., Cassak, P. A., & Kukolich, S. G. (2005). Determination of structural parameters for ferrocenecarboxaldehyde using Fourier transform microwave spectroscopy. Journal of Chemical Physics, 123(5).
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  Abstract: Gas-phase structural parameters for ferrocenecarboxaldehyde have been determined using Fourier transform microwave spectroscopy. Rotational transitions due to a -, b -, and c -type dipole moments were measured. Eighteen rotational constants were determined by fitting the measured transitions of various isotopomers using a rigid rotor Hamiltonian with centrifugal distortion constants. Least-squares fit and Kraitchman analyses have been used to determine the gas-phase structural parameters and the atomic coordinates of the molecule using the rotational constants for various isotopomers. Structural parameters determined from the least-squares fit are the Fe-C bond lengths to the cyclopentadienyl rings, r (Fe-C) =2.047 (4) Å, and the distance between the carbon atoms of the cyclopentadienyl rings, r (C-C) =1.430 (2) Å and r (C1 - C 1′) =1.46 (1) Å of ring carbon and aldehyde carbon atom. Structural parameters were also obtained using density-functional theory calculations, and these were quite helpful in resolving ambiguities in the structural fit analysis, and providing some fixed parameters for the structural analysis. The results of the least squares and the calculations indicate that the carbon atoms of the Cp groups for ferrocenecarboxaldehyde are in an eclipsed conformation in the ground vibrational state. © 2005 American Institute of Physics.
• Subramanlan, R., Karunatilaka, C., Keck, K. S., & Kukolich, S. G. (2005). The gas phase structure of ethynylferrocene using microwave spectroscopy. Inorganic Chemistry, 44(9), 3137-3145.
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  PMID: 15847419;Abstract: Gas phase structural parameters for ethynylferrocene have been determined using microwave spectroscopy, Rotational transitions due to a- and b-type dipole moments were measured. Twenty four rotational constants have been determined by fitting the measured transitions of various isotopomers using a rigid rotor Hamiltonian with centrifugal distortion constants. Least-squares fits to determine structural parameters and Kraitchman analyses have been used to determine the gas phase structural parameters and the atomic coordinates from the rotational constants. The distance between the Fe atom and the C atoms of the cyclopentadienyl rings is r(Fe-C 1) = 2,049(5) Å, and the distance between the carbon atoms of the cyclopentadienyl ring is r(C-C) = 1.432(2) A. The ethynyl group is bent away from the Fe atom and out of the plane of the carbon atoms in the adjacent cyclopentadienyl ring by 2.75(6)°, Structural parameters were also obtained from DFT calculations and Kraitchman analyses, and the results are compared. Analysis of fit results for 13C isotopic substitution data indicates that the carbon atoms of the two cyclopentadienyl rings are in an eclipsed conformation in the ground vibrational state. Trends in microwave experimental values for the distance from the Fe atom to the center of the cyclopentadienyl ring for a series of substituted ferrocenes have been analyzed. This analysis provides an estimate of the gas phase distance from the Fe atom to the centers of the cyclopentadienyl rings for ferrocene of 1.65(1) Å. © 2005 American Chemical Society.
• Tanjaroon, C., Karunatilaka, C., Keck, K. S., & Kukolich, S. G. (2005). Microwave spectroscopy measurements of the gas-phase structure of cyclopentadienyltungsten tricarbonyl hydride. Organometallics, 24(12), 2848-2853.
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  Abstract: High-resolution microwave spectra for 13C isotopomers of cyclopentadienyltungsten tricarbonyl hydride were measured using a pulsed-beam Fourier transform microwave spectrometer system. The new rotational constants for the 13C isotopomers are combined with the previously obtained rotational constants for normal and deuterium isotopomers to obtain the gas-phase structure of cyclopentadienyltungsten tricarbonyl hydride. The new frequencies for the five unique 13C isotopomers were measured in the 5-7 GHz range for C 5H 5W(CO) 3H. Kraitchman analysis and least-squares structure-fitting procedures were used to determine the structural parameters. The results from the structural fit yielded the W-H bond length, r 0(W-H) = 1.79(2) Å, which agrees very well with the previously reported value, r s(W-H) = 1.79(4) Å, obtained with a much smaller data set. The present study also yielded the distance from tungsten to the C 5H 5 ring, r(W-Cp) = 2.03(1) Å, which corresponds to an average W-C (of Cp) bond length of 2.37(2) Å. The experimental ring radius for Cp of r(Cp) = 1.20(2) Å corresponds to an average cyclopentadienyl C-C bond length of 1.423(4) Å. Deviations of near 0.02 Å from C 5 symmetry for the W-C bond lengths for the Cp ligand and smaller deviations for the C-C bond lengths were obtained from the DFT calculations, and incorporating these deviations into the least-squares fit improved the standard deviation by a factor of 5. The average bond length from tungsten to the carbonyl carbons is r(W-CO) = 1.97(2) Å. Results obtained from the structural fit are in very close agreement with the experimental, Kraitchman analysis values. Results from new DFT calculations are given, with heavy-atom coordinates in very good agreement with experimental values, and a slightly shorter calculated W-H bond length, r e(W-H) = 1.73 Å. © 2005 American Chemical Society.
• Daly, A. M., Tanjaroon, C., Marwitz, A. J., Liu, S., & Kukolich, S. G. (2004). Microwave Spectrum, Structural Parameters, and Quadrupole Coupling for 1,2-Dihydro-1,2-azaborine. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 132(15), 5501-5506.
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  The first microwave spectrum for 1,2-dihydro-1,2-azaborine has been measured in the frequency range 7-18 GHz, providing accurate rotational constants and nitrogen and boron quadrupole coupling strengths for three isotopomers, H(6)C(4)(11)B(14)N, H(6)C(4)(10)B(14)N, and H(5)DC(4)(11)B(14)N. The measured rotational constants were used to accurately determine coordinates for the substituted atoms and provide sufficient data to determine most of the important structural parameters for this molecule. The spectra were obtained using a pulsed beam Fourier transform microwave spectrometer, with sufficient resolution to allow accurate measurements of (14)N, (11)B, and (10)B nuclear quadrupole hyperfine interactions. High-level ab initio calculations provided structural parameters and quadrupole coupling strengths that are in very good agreement with measured values. The rotational constants for the parent compound are A = 5657.335(1), B = 5349.2807(5), and C = 2749.1281(4) MHz, yielding the inertial defect Delta(0) = 0.02 amu center dot angstrom(2) for the ground-state structure. The observed near-zero and positive inertial defect clearly indicates that the molecular structure of 1,2-dihydro-1,2-azaborine is planar. The least-squares fit analysis to determine the azaborine ring structure yielded the experimental bond lengths and 2 sigma errors R(B-N) = 1.45(3) angstrom, R(B-C) = 1.51(1) angstrom, and R(N-C) = 1.37(3) angstrom for the ground-state structure. Interbond angles for the ring were also determined. An extended Townes-Dailey population analysis of the boron and nitrogen quadrupole coupling constants provided the valence p-electron occupancy p(c) = 0.3e for boron and p(c) = 1.3e for nitrogen.
• KUKOLICH, S., & SICKAFOOSE, S. (2004). MEASUREMENTS OF THE MICROWAVE-SPECTRUM, RE-H BOND-LENGTH, AND RE QUADRUPOLE COUPLING FOR HRE(CO)5. JOURNAL OF CHEMICAL PHYSICS, 99(9), 6465-6469.
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  Rotational transition frequencies for rhenium pentacarbonyl hydride were measured in the 4-10 GHz range using a Flygare-Balle type microwave spectrometer. The rotational constants and Re nuclear quadrupole coupling constants for the four isotopomers, (1) (HRe(CO)5)-Re-187, (2) (HRe(CO)5)-Re-185, (3) (DRe(CO)5)-Re-187, (4) (DRe(CO)5)-Re-185, were obtained from the spectra. For the most common isotopomer, B(1) = 818.5464(2) MHz and eq Q(Re-187) = -900.13(3) MHz. The Re-H bond length (r0) determined by fitting the rotational constants is 1.80(1) angstrom. Although the Re atom is located at a site of near-octahedral symmetry, the quadrupole coupling is large due to the large Re nuclear moments. A 2.7% increase in Re quadrupole coupling was observed for D-substituted isotopomers, giving a rather large isotope effect on the quadrupole coupling. The C(ax)-Re-C(eq) angle is 96(1)-degrees-, when all Re-C-O angles are constrained to 180-degrees.
• Kukolich, S. G., McCarthy, M. C., & Thaddeus, P. (2004). Molecular Structure of o-Benzyne from Microwave Measurements. Journal of Physical Chemistry A, 108(14), 2645-2651.
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  Abstract: The o-benzyne molecule has been known for many years to be an important, but short-lived, reaction intermediate in substitution reactions and more recently in cyclization reactions of enediynes. Although there has been widespread interest in this transient molecule, previous experimental structural data were very limited. In the present work, rotational transitions for o-benzyne were measured with a pulsed-beam, Fourier transform microwave spectrometer for all unique, singly substituted 13C and single-D isotopomers. The o-benzyne was efficiently produced by flowing a dilute mixture of isotopically enriched benzene in neon through a pulsed-DC discharge beam source. The new data, combined with previous data for the normal isotopomer, provide a complete set of structural parameters for this molecule. The r s substitution coordinates and the coordinates from a least-squares fit are reported and are in good agreement. When using the least-squares fit to obtain structural parameters, correction terms arising from harmonic terms in the vibrational averaging were subtracted from the measured rotational constants to obtain a better representation of the planar equilibrium structure. Further improvements in the fits were obtained by applying small, mass-dependent adjustments to the atom coordinates. Structural parameters obtained from the fit to these modified rotational constants are an acetylenic C 1≡C 2 bond length of 1.264(3) Å, and the other bond lengths C 2-C 33 = 1.390(3) Å, C 3-C 4 = 1.403(3) Å, C 4C 5 = 1.404(3) Å, C 3-H 1 = 1.095(9) Å, and C 4-H 2 = 1.099(4) Å. The C 1≡C 2 bond is only 0.057 Å longer than the free acetylene bond. The other C-C bond lengths are within 0.01 Å of those of benzene C-C bonds. New spectral data for the single-D isotopomers were used to obtain better values for the deuterium quadrupole coupling. Bond-axis deuterium quadrupole coupling constants are eQq zz(D 1) = 188(2) kHz, and eQq zz(D 2) = 185(10) kHz, which agree well with the value for benzene-D 1. The new structural parameters are compared here with theoretical parameters and with an NMR measurement of the C 1--C 2 bond length.
• Kukolich, S., Tanjaroon, C., Keck, K. S., & Kukolich, S. G. (2004). Microwave spectroscopy measurements of rotational spectra and DFT calculations for two distinct structural isomers of 1,1'-dimethylferrocene. Journal of the American Chemical Society, 126(3).
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  Microwave spectra were obtained for two distinct structural isomers of 1,1'-dimethylferrocene, an eclipsed synperiplanar isomer (phi = 0 degrees, the E0 isomer), with A = 1176.9003(2) MHz, B = 898.3343(2) MHz, C = 668.7469(2) MHz, and an eclipsed synclinal isomer (phi = 72 degrees, the E72 isomer) with A = 1208.7117(14) MHz, B = 806.4101(12) MHz, and C = 718.7179(8) MHz. The b-dipole, asymmetric-top spectra of both structural isomers were measured in the frequency range of 5-12 GHz using a Flygare-Balle type of spectrometer. A very good fit to observed transitions, with small distortion constants, was obtained for the E0 conformer, indicating that this conformer is nearly rigid. The deviations obtained in a similar least-squares fit for the E72 confomer are significantly larger, indicating possible fluxional behavior for this conformer. In addition, 7 out of the 26 transitions observed for the E72 isomer conformer clearly exhibit very small splittings, giving further evidence for internal motion. DFT calculations for the different possible conformations of 1,1'- dimethylferrocene arising from rotation of one methyl cyclopentadienyl ligand relative to the other about the nominal C5 axis by an angle phi (dihedral angle) were performed using the B3PW91 functional. The calculations converged and were optimized for five structures on this torsional potential energy surface corresponding to different dihedral angles phi; three yielded energy minima, and two gave energy maxima, corresponding to transition states. The experimental results are in very good agreement with the results of the DFT calculations.
• Kukolich, S., Tanjaroon, C., Keck, K. S., Sebonia, M. M., Karunatilaka, C., & Kukolich, S. G. (2004). Microwave spectra and the metal-hydrogen bond lengths for the C5H5Mo(CO)3H and C5H5W(CO)3H complexes. The Journal of chemical physics, 121(3).
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  The measurements of rotational spectra and metal-hydrogen bond lengths for molybdenum and tungsten hydride complexes were recently completed in our laboratory. The W-H and Mo-H bond lengths were obtained from high resolution rotational spectra of C5H5Mo(CO)3H, C5H5W(CO)3H, C5H5Mo(CO)3D, and C5H5W(CO)3D. Data for five molybdenum and four tungsten isotopomers were obtained for both the normal and deuterium-substituted species. The asymmetric-top rotational parameters A, B, C, DeltaJ, and deltaJ were determined from the least-squares fits and these results indicate that the structures of these complexes are nearly rigid. The hydrogen bond lengths were determined for both complexes using Kraitchman analyses. The molybdenum-hydrogen bond length for the C5H5Mo(CO)3H complex is rMo-H=1.80(1) A. The tungsten-hydrogen bond length for the C5H5W(CO)3H complex is rW-H=1.79(4) A. Density functional theory (DFT) calculations of the structures were performed to obtain the optimized theoretical structures for C5H5Mo(CO)3H and C5H5W(CO)3H. Results obtained from the DFT calculations are in good agreement with the experimental parameters, and the Mo-H value is in good agreement with previously reported Mo-H bond lengths for similar complexes.
• Palmer, M. H., Camp, P. J., Tanjaroon, C., Keck, K. S., & Kukolich, S. G. (2004). A theoretical study of the staggered and eclipsed forms of the dinuclear complex Mn Re(CO) ₁₀. Journal of Chemical Physics, 121(15), 7187-7194.
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  PMID: 15473786;Abstract: Two possible conformers of the dinuclear complex MnRe(CO) 10, each of C 4v symmtery, with eclipsed and staggered conformations, were theoretically studied. The staggered form was found to be lower in energy using both the B3LYP and BP86 density functionals. It was shown that the computed bond lengths, bond angles and rotational constant for the staggered conformation compare favorably with the results from microwave experiments. Several basis sets, with both analytical and finite difference methods were used to determine the harmonic frequencies for the staggered structure.
• Palmer, M. H., Camp, P. J., Tanjaroon, C., Keck, K. S., & Kukolich, S. G. (2004). A theoretical study of the staggered and eclipsed forms of the dinuclear complex Mn Re(CO)10. The Journal of chemical physics, 121(15), 7187-94.
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  Two possible conformers of the dinuclear complex Mn Re(CO)10, each of C(4v) symmetry, with eclipsed and staggered conformations, have been analyzed theoretically. Using both the B3LYP and BP86 density functionals we find that the staggered form is lower in energy. A determination of the B3LYP potential energy surface as a function of the Mn-Re distance is presented for both conformers. The computed bond lengths, bond angles, and rotational constant for the staggered conformation compare favorably with the results from microwave experiments. The harmonic frequencies for the staggered structure have been determined using several basis sets, with both analytical and finite difference methods. These unscaled vibrational frequencies, together with their intensities for both infrared and Raman activity, are used to assign the three most intense experimental IR and Raman bands, and in particular, the nu(CO) region. The lowest A(2) vibration was calculated to occur at 41 cm(-1) in the staggered conformer; this frequency becomes imaginary in the (saddle point) eclipsed form. Several fundamentals remain to be observed experimentally.
• Tanjaroon, C., Keck, K. S., & Kukolich, S. G. (2004). Microwave Spectroscopy Measurements of Rotational Spectra and DFT Calculations for Two Distinct Structural Isomers of 1,1′-Dimethylferrocene. Journal of the American Chemical Society, 126(3), 844-850.
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  PMID: 14733559;Abstract: Microwave spectra were obtained for two distinct structural isomers of 1,1′-dimethylferrocene, an eclipsed synperiplanar isomer (ψ = 0°, the E0 isomer), with A = 1176.9003(2) MHz, B = 898.3343(2) MHz, C = 668.7469(2) MHz, and an eclipsed synclinal isomer (ψ = 72°, the E72 isomer) with A = 1208.7117(14) MHz, B = 806.4101(12) MHz, and C = 718.7179(8) MHz. The b-dipole, asymmetric-top spectra of both structural isomers were measured in the frequency range of 5-12 GHz using a Flygare-Balle type of spectrometer. A very good fit to observed transitions, with small distortion constants, was obtained for the E0 conformer, indicating that this conformer is nearly rigid. The deviations obtained in a similar least-squares fit for the E72 confomer are significantly larger, indicating possible fluxional behavior for this conformer. In addition, 7 out of the 26 transitions observed for the E72 isomer conformer clearly exhibit very small splittings, giving further evidence for internal motion. DFT calculations for the different possible conformations of 1,1′-dimethylferrocene arising from rotation of one methyl cyclopentadienyl ligand relative to the other about the nominal C5 axis by an angle ψ (dihedral angle) were performed using the B3PW91 functional. The calculations converged and were optimized for five structures on this torsional potential energy surface corresponding to different dihedral angles ψ; three yielded energy minima, and two gave energy maxima, corresponding to transition states. The experimental results are in very good agreement with the results of the DFT calculations.
• Tanjaroon, C., Keck, K. S., Kukolich, S. G., Palmer, M. H., & Guest, M. F. (2004). The rotational spectrum and theoretical study of a dinuclear complex, MnRe(CO) ₁₀. Journal of Chemical Physics, 120(10), 4715-4725.
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  PMID: 15267332;Abstract: The rotational spectrum of a dinuclear complex was studied using high-resolution pulsed beam microwave spectrometers. The rotational spectrum of MnRe(CO) 10 were measured and analyzed to obtain the gas phase molecular parameters of the complex. It was observed that the solid phase could be due to the presence of the crystal packing forces in the crystal. The results suggest that the Mn-Re bond is slightly larger than the sum of the covalent radii.
• Tanjaroon, C., Keck, K. S., Kukolich, S. G., Palmer, M. H., & Guest, M. F. (2004). The rotational spectrum and theoretical study of a dinuclear complex, MnRe(CO)(10). The Journal of chemical physics, 120(10), 4715-25.
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  The first rotational spectrum of a dinuclear complex, MnRe(CO)(10), has been obtained using a high-resolution pulsed beam microwave spectrometer. Sixty-four hyperfine components of the J=11-->J(')=12 and J=12-->J(')=13 rotational transitions were measured for two rhenium isotopomers. The B values obtained from the experiment are B=200.36871(18) MHz for the (187)Re isotopomer and B=200.5561(10) MHz for the (185)Re isotopomer. The measured rotational constants are in reasonably good agreement with the B values calculated from the x-ray diffraction structural data, and from theoretical calculations. The gas-phase Mn-Re bond distance is approximately 2.99 A, and the calculated value is only slightly longer. The experimental quadrupole coupling constant for the manganese atom is eQq(aa) ((55)Mn)=-16.52(5) MHz, and the corresponding quadrupole coupling constants for the two rhenium isotopomers are eQq(aa) ((187)Re)=370.4(4) MHz and eQq(aa) ((185)Re)=390.9(6) MHz. The quadrupole coupling constants were also determined from a variety of theoretical calculations, with very large Gaussian orbital bases. The best estimates, at a nonrelativistic level, are eQq(aa) ((55)Mn)=0.68 MHz and eQq(aa) ((187)Re)=327.6 MHz with a 874 GTO basis set, but the results are very basis set dependent, especially the sign of the Mn quadrupole coupling. Very slight bending of angles MnC(eq)O(eq) and ReC(eq)O(eq) angles is found in the calculations.
• Tanjaroon, C., Keck, K. S., Sebonia, M. M., Karunatilaka, C., & Kukolich, S. G. (2004). Microwave spectra and the metal-hydrogen bond lengths for the C ₅H ₅Mo(CO) ₃H and C ₅H ₅W(CO) ₃H complexes. Journal of Chemical Physics, 121(3), 1449-1453.
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  PMID: 15260689;Abstract: The microwave spectra and the metal-hydrogen bond lengths for the C 5H 5Mo(CO) 3H and C 5H 5W(CO) 3H complexes were analyzed. The sample was heated to produce vapor pressure before pulsing of the sample into the microwave cavity. Measurement of rotational frequencies in the range of 4-12 GHz were performed using a pulsed beam fourier transform microwave spectrometer. Result shows that the Mo-H value is in good agreement with the x ray and neutron diffraction studies of similar complexes.
• Tanjaroon, C., Subramanian, R., Karunatilaka, C., & Kukolich, S. G. (2004). Microwave measurements of ¹⁴N and D quadrupole coupling for (Z)-2-hydroxypyridine and 2-pyridone tautomers. Journal of Physical Chemistry A, 108(44), 9531-9539.
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  Abstract: Rotational spectra for the two tautomers (Z)-2-hydroxypyridine and 2-pyridone and their deuterated isotopomers were measured in the microwave range between 4 and 14 GHz using a pulsed beam Fourier transform microwave spectrometer. Nitrogen and deuterium quadrupole hyperfine structure was completely resolved for many of the observed transitions, and the measured 14N quadrupole coupling tensors are quite different for these two tautomers. The eQq cc(N) values have opposite signs. The 14N quadrupole coupling strengths for (Z)-2-hydroxypyridine in the principal inertial axis system are as follows: eQq aa(N) = -0.076(11), eQq bb(N) = -2.283(6), and eQq cc(N) = 2.359(6) MHz. The 14N and D nuclear quadrupole coupling strengths for (Z)-2-deuteriohydroxypyridine in the principal inertial axis are eQq aa(N) = -0.1465(4), eQq bb(N) = -2.2045-(4), and eQq cc(N) = 2.3510(4) MHz and eQq aa(D) = -0.0250(9), eQq bb(D) = 0.1699(4), and eQq ccD) = -0.1449(4) MHz. The 14N quadrupole coupling strengths for 2-pyridone in the principal inertial axis system are eQq aa(N) = 1.496(4), eQq bb(N) = 1.269(4), and eQq cc(N) = -2.765(4) MHz. The 14N and D nuclear quadrupole coupling strengths for 1-deuterio-2-pyridone in the principal inertial axis system are as follows: eQq aa(N) = 1.511(2), eQq bb(N) = 1.249(5), and eQq cc(N) = -2.759(5) MHz and eQq aa(D) = -0.110(7), eQq bb(D) = 0.354(6), and eQq cc(D) = -0.244(6) MHz. New, improved, experimental rotational constants were obtained for the H and D isotopomers of both tautomers. Kraitchman analysis indicates the "tautomeric" hydrogen atom is at a distance of 2.653(2) A in 2-hydroxypyridine and a distance of 2.124(1) Å in 2-pyridone from the centers of mass of the two tautomers, respectively. The DFT calculated eQq(N) values for both the tautomers and the deuterated tautomers are in good agreement with the present experimental values. The Townes-Dailey model has been used to analyze the new quadrupole coupling data of the tautomers and the results are presented in terms of nitrogen atom p-orbital occupation numbers.
• Kukolich, S. G., Tanjaroon, C., McCarthy, M. C., & Thaddeus, P. (2003). Microwave spectrum of o-benzyne produced in a discharge nozzle. Journal of Chemical Physics, 119(8), 4353-4359.
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  Abstract: A pulsed-nozzle electric discharge source was used to efficiently produce o-benzyne. High-resolution measurements of transition frequencies, rotational constants, and distortion constants, for five isotopomers, and deuterium quadupole coupling interaction parameters were determined.
• Kukolich, S., Tanjaroon, C., McCarthy, M., & Thaddeus, P. (2003). Microwave spectrum of o-benzyne produced in a discharge nozzle. JOURNAL OF CHEMICAL PHYSICS, 119(8), 4353-4359.
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  The microwave spectrum for o-benzyne was obtained by passing a dilute (
• Earp, J. C., Margolis, D. S., Tanjaroon, C., Bitterwolf, T. E., & Kukolich, S. G. (2002). The microwave spectrum of cyclopentadienyl niobium tetracarbonyl. Journal of Molecular Spectroscopy, 211(1), 82-85.
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  Abstract: Rotational transitions for the symmetric-top transition metal complex C5H5Nb(CO)4 were measured using a Flygare-Balle- type pulsed-beam microwave spectrometer. The spectrum indicates that in the gas phase, this complex is a prolate symmetric top with B = C = 558.842(4) MHz. Transitions were measured in the range 4-12 GHz. The observed splittings due to 93Nb quadrupole coupling were smaller than expected, with eq Q(93Nb) = -1.8(6) MHz. The value DJ = 0.04(2) kHz. No evidence for fluxional behavior was observed. The A rotational constant, calculated from the X-ray data, is A = 670(30) MHz and calculated B and C constants are in agreement with the present microwave values. This appears to be the first measurement of a microwave spectrum and gas-phase quadrupole coupling for a 93Nb organometallic complex. © 2002 Elsevier Science.
• Margolis, D. S., Tanjaroon, C., & Kukolich, S. G. (2002). Measurements of microwave spectra and structural parameters for methylferrocene. Journal of Chemical Physics, 117(8), 3741-3747.
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  Abstract: Measurements of microwave spectra and structural parameters for methyl ferrocene were presented. The experiment was undertaken using a pulsed-beam Fourier transform spectrometer. 59 transitions were measured for the normal isotopomer. The structural parameters for methylferrocene were determined by rotational constants. Distortions of the substituted cyclopentadienyl ligand were found to be smaller than those of chloroferrocene.
• Drouin, B. J., Dannemiller, J. J., & Kukolich, S. G. (2000). Structural characterization of anti- and syn-allyltricarbonyliron bromide: Rotational spectra, quadrupole coupling, and density functional calculations. Inorganic Chemistry, 39(4), 827-835.
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  PMID: 11272584;Abstract: Rotational transitions for two distinct structural isomers of allyltricarbonyliron bromide have been clearly observed in the cold molecular beam of a pulsed-beam Fourier transform microwave spectrometer. Rotational transitions exhibiting quadrupole splitting patterns for each isomer were measured for the 79Br and 81Br isotopomers. Both isomers are accidental near-prolate symmetric tops. The measured rotational constants for the 79Br isotopomer are A(anti) = 920.6148(2) MHz, B(anti) = 582.8866(12) MHz, C(anti) = 581.3027(12) MHz, A(syn) = 919.5055(1) MHz, B(syn) = 584.1865(1) MHz, and C(syn) = 581.6392(1) MHz. Analysis of the isotopic substitution data and possible transition assignments indicates that these molecules have C(s) symmetry. Both isomers are found to have a dipole component along the a axis. However, the anti isomer has a 'c' type dipole component, whereas a 'b' dipole component is found for the syn isomer. It was found necessary to carefully analyze both rotational constants and the quadrupole coupling data in order to determine the correct assignment of dipole moment components for each isomer. This change in dipole assignments implies that there is a switch of inertial axes upon isomerization resulting from a subtle shift of the allyl center of mass coordinates, upon reorientation of the allyl ligand. The X-ray and DFT calculated structures for the anti isomer are in excellent agreement with the present data. No previous structural data for the syn isomer were available, and the present analysis strongly supports the expected conformation.
• Drouin, B. J., Dannemiller, J. J., & Kukolich, S. G. (2000). Structural characterization of anti- and syn-allyltricarbonyliron bromide: rotational spectra, quadrupole coupling, and density functional calculations. Inorganic chemistry, 39(4), 827-35.
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  Rotational transitions for two distinct structural isomers of allyltricarbonyliron bromide have been clearly observed in the cold molecular beam of a pulsed-beam Fourier transform microwave spectrometer. Rotational transitions exhibiting quadrupole splitting patterns for each isomer were measured for the 79Br and 81Br isotopomers. Both isomers are accidental near-prolate symmetric tops. The measured rotational constants for the 79Br isotopomer are A(anti) = 920.6148(2) MHz, B(anti) = 582.8866(12) MHz, C(anti) = 581.3027(12) MHz, A(syn) = 919.5055(1) MHz, B(syn) = 584.1865(1) MHz, and C(syn) = 581.6392(1) MHz. Analysis of the isotopic substitution data and possible transition assignments indicates that these molecules have Cs symmetry. Both isomers are found to have a dipole component along the a axis. However, the anti isomer has a "c" type dipole component, whereas a "b" dipole component is found for the syn isomer. It was found necessary to carefully analyze both rotational constants and the quadrupole coupling data in order to determine the correct assignment of dipole moment components for each isomer. This change in dipole assignments implies that there is a switch of inertial axes upon isomerization resulting from a subtle shift of the allyl center of mass coordinates, upon reorientation of the allyl ligand. The X-ray and DFT calculated structures for the anti isomer are in excellent agreement with the present data. No previous structural data for the syn isomer were available, and the present analysis strongly supports the expected conformation.
• Drouin, B. J., Dannemiller, J. J., & Kukolich, S. G. (2000). The gas-phase structure of chloroferrocene from microwave spectra. Journal of Chemical Physics, 112(2), 747-751.
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  Abstract: Rotational spectra for ten isotopomers of chloroferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Rotational transitions due to both "a" and "b" dipole moments were measured in the 4-12 GHz range. Thirty rotational constants were determined from microwave data for the normal, 54Fe, 57Fe, 37Cl, and six unique 13C isotopomers, by fitting the microwave data using a rigid rotor Hamiltonian with centrifugal distortion and quadrupole coupling terms. The moments of inertia of the isotopomers were used in Kraitchman and in least-squares fitting analyses to determine gas-phase structural parameters. The unsubstituted cyclopentadienyl (C5H5) ligand was determined to have essentially fivefold local symmetry, while the chlorinated cyclopentadienyl ligand shows small, but significant distortions from the fivefold symmetry. The C-Cl bond is bent 2.7(6)° from the plane of carbon atoms. This substituted C5H4Cl ligand is tilted 1.4(5)° with respect to the unsubstituted C5H5 ligand. The carbon atoms of the two cyclopentadienyl ligands are eclipsed, similar to normal ferrocene. The average Fe-C distance is 2.042(9) Å. The estimated displacement of C-H bonds out of the planes of the carbon atoms is 4(2)° away from the metal atom. © 2000 American Institute of Physics.
• Kukolich, S. G., Drouin, B. J., Indris, O., Dannemiller, J. J., Zoller, J. P., & Herrmann, W. A. (2000). Microwave spectra, density functional theory calculations and molecular structure of acetylenemethyldioxorhenium. Journal of Chemical Physics, 113(18), 7891-7900.
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  Abstract: The rotational spectra of 14 isotopomers was used to investigate the molecular structure of acetylenemethyldioxorhenium. The catalyzed reactions of methyltrioxorhenium and osmium tetroxide related the complex to its intermediates. Microwave spectrometers of the Flygare-Balle type were used for the structural analysis. The rotational constants were found in correlation with the density functional theory.
• CHOE, J., KWAK, D., & KUKOLICH, S. (1999). FOURIER-TRANSFORM SPECTRA OF THE 2100-CM-1 BANDS OF HCN. JOURNAL OF MOLECULAR SPECTROSCOPY, 121(1), 75-83.
• Drouin, B. J., & Kukolich, S. G. (1999). Microwave spectra and the molecular structure of tetracarbonylethyleneiron. Journal of the American Chemical Society, 121(16), 4023-4030.
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  Abstract: Microwave spectra of seven isotopomers of tetracarbonylethyleneiron were recorded using a Pulse-Beam Fourier Transform Microwave Spectrometer. Rotational transitions for a 'c' dipole moment with J' ← J from 2 ← I to 6 ← 5 were measured in the 4-12 GHz range. Rotational constants were determined by fitting the measured microwave spectra to a Watson 'A' reduced Hamiltonian with centrifugal distortion parameters. The measured rotational constants of the main isotopomer are A = 1031.1081(4) MHz, B = 859.8055(4) MHz, and C = 808.5675(3) MHz. Data were also obtained for three 13C- substituted species and two 18O-substituted species in natural abundance. Additional spectra were measured for an isotopically enriched sample of perdeuterated tetracarbonylethyleneiron. The moments of inertia of the seven isotopomers were used in a Kraitchman analysis and in two different least- squares fitting analyses to determine the molecular structure of the compound. The ethylene ligand exhibits significant structural changes upon complexation to iron, primarily an increase in C-C bond length with movement of the hydrogen atoms away from the metal center. The CC and CH bond lengths were found to be r(o) = 1.419(7) and = 1.072(4) Å, respectively. The CCH angle and the FeCCH dihedral angle were found to be
• Drouin, B. J., & Kukolich, S. G. (1998). Molecular structure of tetracarbonyldihydroiron: Microwave measurements and density functional theory calculations. Journal of the American Chemical Society, 120(27), 6774-6780.
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  Abstract: Microwave spectra of seven isotopomers of tetracarbonyldihydroiron were measured in the 4-16 GHz range using a Flygare-Balle type microwave spectrometer. Measured transitions were fit using a rigid rotor Hamiltonian with five independent distortion constants. Structural parameters from a least-squares fit to the rotational constants are r(Fe-H) = 1.576(64) Å, r(Fe-C1) = 1.815(54) Å, r(Fe-C3 = 1.818(65) Å, r(C1-O1) = 1.123(80) Å, r(C3-O3) = 1.141(74) Å,
• Drouin, B. J., Cassak, P. A., & Kukolich, S. G. (1998). Microwave measurements of rhenium quadrupole coupling in cyclopentadienyl rhenium tricarbonyl. Journal of Chemical Physics, 108(21), 8878-8883.
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  Abstract: Microwave measurements of rotational transitions for cyclopentadienyl rhenium tricarbonyl were performed in the gas phase using pulsed beam Fourier transform microwave spectroscopy. One hundred and sixty five transitions were assigned to two isotopomers of rhenium. The location of the rhenium atom near the center of mass produced significant overlap between the spectra of the two isotopomers. The data were accurately fit using a symmetric top, rigid rotor Hamiltonian that included nuclear quadrupole coupling and centrifugal distortion constants. The rotational constants obtained were B(187Re) = 724.9794(2), B(185Re) = 724.9795(2). The quadrupole coupling constants obtained were eQq(187Re) = 614.464(12) and eQq(185Re) = 649.273(14) MHz. The successful fitting of the measured spectra to a symmetric top Hamiltonian indicates that the cyclopentadienyl group retains C5v symmetry, and the Re(CO)3 group C3v symmetry in the gas phase. The measured rotational constants are in reasonable agreement with those calculated from the structural parameters obtained in the earlier x-ray work. The Re quadrupole coupling constants obtained are compared with values for other complexes. © 1998 American Institute of Physics.
• KUKOLICH, S. (1998). HYPERFINE STRUCTURE OF N15H3. PHYSICAL REVIEW, 172(1), 59-&.
• Kukolich, S. G., Drouin, B. J., Cassak, P., & Hubbard, J. L. (1998). Microwave measurements and calculations on cyclopentadienylrhodium dicarbonyl, a V₁₀ hindered rotor. Organometallics, 17(18), 4105-4109.
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  Abstract: The microwave rotational spectrum of (η5-C5H5)Rh(CO)2 was measured in the 5-15 GHz range using a Flygare-Balle type spectrometer system. Attempts to fit the spectrum using a rigid-rotor model resulted in large deviations between measured and calculated frequencies and an unreasonably large A rotational constant. A better fit, including more transitions, was obtained using a V10-barrier hindered rotor Hamiltonian, and a much more reasonable A rotational constant was obtained. The barrier height obtained is V10 = 347(13) GHz (0.14 kJ mol-1). The rotational constants are A = 1613(10) MHz, B = 1046.7(7) MHz, and C = 759.7(10) MHz. Quantum-mechanical calculations using the DFT options in Gaussian 94 provided structural parameters in good agreement with measurements and a barrier height V10 = 272 GHz (0.11 kJ mol-1). The calculated structure showed C2-symmetry distortions of the cyclopentadienyl moiety, in agreement with previous X-ray data for Cp*Rh(CO)2. The calculated rotational constants and V10 barrier height are in good agreement with the experimental results. The calculations indicate that there is coupling between the internal rotation and distortions of the Cp ligand, and this could very likely provide the major contribution to deviations between the hindered-rotor calculated frequencies and the measured frequencies.
• Lavaty, T. G., Wikrent, P., Drouin, B. J., & Kukolich, S. G. (1998). Microwave measurements and calculations on the molecular structure of tetracarbonyldihydroruthenium. Journal of Chemical Physics, 109(21), 9473-9478.
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  Abstract: The microwave rotational spectra for seven isotopomers of tetracarbonyldihydroruthenium were measured in the 4-12 GHz range using a Flygare-Balle type microwave spectrometer. The measured transition frequencies could be fit to within a few kilohertz using a rigid rotor Hamiltonian with centrifugal distortion. The rotational constants for the most abundant isotopomer are A=1234.2762(4), B=932.7016(6), and C=811.6849(6)MHz. The dipole moment is aligned with the c axis of the complex. The 21 measured rotational constants were used to determine the following structural parameters: r(Ru-H)=1.710(23)Å, r(Ru-C1)=1.952(21)Å, r(Ru-C3)=1.974(28)Å, (H-Ru-H)=87.4(2.4)°, (C1-Ru-C2)=160.6(4.3)°, (C3-Ru-C4)=101.4(1.5)°, and (Ru-C1-O1)=172.6(7.6)°. The axial carbonyl groups are bent slightly toward the hydrogen atoms. These structural parameters are in excellent agreement with the substitution coordinates determined from the Kraitchman equations, and with the structural parameters calculated using density functional theory. There was no previous structural data on this complex. The results of the microwave data and theoretical calculations both indicate C2v molecular symmetry, and show that the H atoms are separated by about 2.36 Å. These results indicate that this complex is clearly a "classical dihydride" rather than an η2-bonded, "dihydrogen" complex. Fairly large deuterium isotope effects were observed for the Ru-H bond length and H-Ru-H angle. The r0, Ru-D bond lengths were observed to be 0.03(2) Å shorter than the r0, Ru-H bond lengths. The D-Ru-D angle is 1.1° less than the H-Ru-H angle indicating that the anharmonicity effects are comparable for the bond lengths and for the interbond angle. The new results on this complex are compared with previous results on the similar dihydride complexes, H2Fe(CO)4, and H2Os(CO)4. © 1998 American Institute of Physics.
• Drouin, B. J., Cassak, P. A., & Kukolich, S. G. (1997). Measurements of Structural and Quadrupolar Coupling Parameters for Chloroferrocene Using Microwave Spectroscopy. Inorganic Chemistry, 36(13), 2868-2871.
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  Abstract: Rotational spectra for two isotopomers of chloroferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Transitions were observed for 35Cl and 37Cl isotopomers in the 4-10 GHz range. Chlorine quadrupole coupling strengths and rotational constants were obtained from the data. The rotational constants and quadrupole coupling strengths for 35Cl are A = 1370.009(8) MHz, B = 767.342(1) MHz, C = 634.8834(6) MHz, eQqaa = -9.06(4) MHz, and eQqbb = -28.43(6) MHz and for 37Cl are A = 1362.23(2) MHz, B = 751.623(2) MHz, C = 622.324(1) MHz, eQqaa = -8.78(18) MHz, and eQqbb, = -20.76(9) MHz. These measured rotational constants were used to determine the following structural parameters of chloroferrocene: r(Fe-(C5H5)) = 1.594(20) Å, r(Fe-(C5H4Cl)) = 1.699(13) Å, r(C-C) = 1.7204(9) Å, and r(C-C) = 1.4329(7) Å. No evidence for internal rotation was observed in the microwave spectrum.
• Drouin, B. J., Cassak, P. A., Briggs, P. M., & Kukolich, S. G. (1997). Determination of structural parameters for the half-sandwich compounds cyclopentadienyl thallium and cyclopentadienyl indium and indium quadrupole coupling for cyclopentadienyl indium using microwave spectroscopy. Journal of Chemical Physics, 107(10), 3766-3773.
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  Abstract: Microwave rotational transitions for J′←J=2←1 and 3←2 were measured in the 7-11 GHz range for three isotopomers of (C5H5)In. Similar transitions (up to J′←J=5←4) for eight isotopomers of (C5H5)Tl were measured in the 5-15 GHz range. The rotational constants of the most abundant isotopomers are B(Cp 203Tl)=1467.9730(11) MHz, B(Cp 205Tl) =1465.0723(14) MHz, B(Cp 113In)=1809.9785(30) MHz, and B(Cp 115In)=1800.8199(18) MHz (Cp=C5H5). The quadrupole coupling strengths for the indium compounds are eQq(Cp 113In)=-118.397(69) MHz and eQq(Cp 115In)=-119.981(31) MHz. Spectra for single-substitution 13C isotopomers were seen in natural abundance. Deuterated samples of CpTl were prepared to obtain spectra for deuterium-substituted isotopomers. Analysis of the spectra allowed the determination of the following structural parameters; for (C5H5)Tl, r(Tl-C5) =2.413(3) Å, r(C-C)=1.421(10) Å, r(C-H)=1.082(9) Å and 〈C5-H=0.9(2)° (C5 represents the planar, 5-carbon ring of C5H5), and for (C5H5)In, r(In-C5)=2.314(4) Å and r(C-C)=1.426(6) Å. A Kraitchman analysis was performed on the available isotopomers for comparison of r0 and rs values. Both structural analyses indicate that the hydrogen atoms in (C5H5)Tl are bent slightly out of the carbon plane away from the coordinated metal atom. © 1997 American Institute of Physics.
• Drouin, B. J., Drouin, B. J., Lavaty, T. G., Lavaty, T. G., Cassak, P. A., Cassak, P. A., Kukolich, S. G., & Kukolich, S. G. (1997). Measurements of structural and quadrupole coupling parameters for bromoferrocene using microwave spectroscopy. Journal of Chemical Physics, 107(17), 6541-6548.
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  Abstract: Rotational spectra for two isotopomers of bromoferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Transitions were observed for the 79Br and 81Br isotopomers in the 5-9 GHz range. Rotational constants and the quadrupole coupling tensors were obtained from the data. The rotational constants and quadrupole coupling parameters for 79Br are A=1272.110(1), B=516.1125(2), C=441.3775(2), eQqaa=267.16(3), eQqab=-409.81(4), and eQqbb=21.49(4), and those for 81Br are A=1271.045(4), B=510.0079(2), C =436.7687(2), eQq aa=225.40(6), eQqab=-341.62(4), and eQqbb=15.65(4). The measured rotational constants were used to determine the following structural parameters of bromoferrocene: r(Fe-(C5H5))=1.63(2), r(Fe-(C5H4Br))=1.67(3), r(C-Br)=1.875( 11), and r (C-C) =1.433(1) Å. The values of the quadrupole coupling parameters in the principal quadrupole axis systems and the C-Br bond axis systems are compared with similarly derived parameters for chloroferrocene, chlorobenzene, and bromobenzene. Previous data for chloroferrocene has been reanalyzed to obtain refined quadrupole parameters. © 1997 American Institute of Physics.
• KUKOLICH, S., ROEHRIG, M., HAUBRICH, S., & SHEA, J. (1997). MICROWAVE MEASUREMENTS OF COBALT AND NITROGEN QUADRUPOLE COUPLING IN CO(CO)3NO. JOURNAL OF CHEMICAL PHYSICS, 94(1), 191-194.
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  J = 2 --> 3, 3 --> 4, 4 --> 5, and 5 --> 6 transtions in the oblate symmetric top molecule cobalt tricarbonyl nitrosyl were measured using a Flygare-Balle type pulsed beam microwave spectrometer. K = 0 and K = 3 transitions were observed for J = 3 --> 4 and 4 --> 5. Hyperfine structure due to Co-59 and N-14 nuclear quadrupole coupling interactions was well resolved. The measured quadrupole coupling strengths are eQq(cc) (Co-59) = 35.14(30) MHz and eQq(cc) (N-14) = -1.59(10). Measured rotation and distortion constants are B0 = 1042.1590(4) MHz and D(j) = 0.17(8) kHz. The measured B value is 4% smaller than the B value calculated from electron diffraction data. Spin-rotation and a quadrupole distortion term were also obtained for Co-59.
• Kukolich, S. G., Breckenridge-Estes, S., & Sickafoose, S. M. (1997). Gas-Phase Iron Tricarbonyl Cyclooctatetraene Exhibits a "Rigid-Rotor" Microwave Spectrum. Inorganic Chemistry, 36(22), 4916-4918.
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  Abstract: The microwave rotational spectrum of (μ4-C8H8) Fe(CO)3 was measured in the 4-12 GHz range using a pulsed- beam, Fourier transform spectrometer system. Nearly all strong transitions can be fit using a near-rigid-rotor model with very small centrifugal distortion terms. These results indicate that this complex has a fairly rigid structure in the gas phase, with no observed evidence for fluxional behavior or internal rotation on the microwave time scale (τ < 10-4 s). These gas-phase observations initially appeared to be in sharp contrast to the solution NMR studies, where this complex is observed to be a "ring whizzer" with cyclic 1,2 carbon shifts. Further analysis indicates these two sets of measurements are compatible since, with an intermediate level barrier to internal motion (V > 500 cm-1), the structure would appear rigid on the microwave time scale, yet could appear quite fluxional on the much longer NMR time scale. The rotational constants are A = 825.2559(2), B = 510.5149- (1), and C = 462.5246(1) MHz. Centrifugal distortion constants are ΔJ = 0.0146(5), ΔJK = 0.015(3), ΔK = 0.049(4), δJ = 0.0034(3), and δK = -0.092(6) kHz. The measured rotational constants all agree with those calculated from the X-ray structure to within 0.3%. The excellent agreement between the rotational constants makes it very likely that the solid-state and gas-phase structures are nearly identical.
• Kukolich, S., Drouin, B. J., Cassak, P. A., & Kukolich, S. G. (1997). Measurements of Structural and Quadrupolar Coupling Parameters for Chloroferrocene Using Microwave Spectroscopy. Inorganic chemistry, 36(13).
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  Rotational spectra for two isotopomers of chloroferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Transitions were observed for (35)Cl and (37)Cl isotopomers in the 4-10 GHz range. Chlorine quadrupole coupling strengths and rotational constants were obtained from the data. The rotational constants and quadrupole coupling strengths for (35)Cl are A = 1370.009(8) MHz, B = 767.342(1) MHz, C = 634.8834(6) MHz, eQq(aa)() = -9.06(4) MHz, and eQq(bb)() = -28.43(6) MHz and for (37)Cl are A = 1362.23(2) MHz, B = 751.623(2) MHz, C = 622.324(1) MHz, eQq(aa)() = -8.78(18) MHz, and eQq(bb)() = -20.76(9) MHz. These measured rotational constants were used to determine the following structural parameters of chloroferrocene: r(Fe-(C(5)H(5))) = 1.594(20) Å, r(Fe-(C(5)H(4)Cl)) = 1.699(13) Å, r(C-Cl) =1.7204(9) Å, and r(C-C) = 1.4329(7) Å. No evidence for internal rotation was observed in the microwave spectrum.
• Wikrent, P., Drouin, B. J., Kukolich, S. G., Lilly, J. C., Ashby, M. T., Herrmann, W. A., & Scherer, W. (1997). Measurements of the structure of methyltrioxorhenium using microwave spectroscopy. Journal of Chemical Physics, 107(7), 2187-2192.
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  Abstract: The rotational spectra for six isotopomers of methyltrioxorhenium (MTO) were measured in the 6-14 GHz range using a Flygare-Balle-type pulsed-beam microwave spectrometer. The measured transition frequencies were analyzed to obtain rotational constants and quadrupole coupling strengths. Rotational constants from the new measurements were used, along with previous results for the normal and 13C isotopomers, to determine the complete, three-dimensional structure for MTO. The bond lengths obtained are r(Re-C)=2.074(4) Å, r(Re-O)=1.703(2) Å, and r(C-H)=1.088(7) Å. The interbond angles are 〈Re-C-H=108.9(2)° and 〈C-Re-O =106.4(4)°. This complex appears to have C3v symmetry in the gas phase, unlike the solid-state structure. Structural parameters are compared with neutron-diffraction, electron-diffraction, and density functional theory results. Spectra for the asymmetric-top isotopomers were much more difficult to analyze due to effects of off-diagonal quadrupole coupling terms and possible internal rotation. The Re quadrupole coupling strength is increased by 1.4% for CD3ReO3 compared with CH3ReO3, illustrating a secondary isotope effect. © 1997 American Institute of Physics.
• KUKOLICH, S. (1996). MICROWAVE STRUCTURE MEASUREMENTS ON THE CYCLOPROPANE-HCN COMPLEX. JOURNAL OF CHEMICAL PHYSICS, 78(8), 4832-4835.
• KUKOLICH, S. (1996). MOLECULAR BEAM MEASUREMENT OF MAGNETIC SUSCEPTIBILITY ANISOTROPIES AND MOLECULAR QUADRUPOLE MOMENT IN H2CO. JOURNAL OF CHEMICAL PHYSICS, 54(1), 8-&.
• Kukolich, S. G., & Sickafoose, S. M. (1996). Microwave measurements of the gas-phase molecular structure of cobalt tetracarbonyl hydride. Journal of Chemical Physics, 105(9), 3466-3471.
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  Abstract: Microwave rotational spectra for six isotopomers of HCo(CO)4 were measured using a Flygare-Balle type spectrometer. Transitions were measured in the 4-10 GHz range. The data were analyzed to obtain rotational constants, 59Co quadrupole coupling strengths, distortion constants and spin-rotation interaction strengths. The common isotopomer is clearly a symmetric top, with C3v symmetry. For the common isotopomer 5 = 1131.7212(9) MHz and eQq(59Co)=116.62(3) MHz. The rotational constants were used to determine the complete, three-dimensional structure of this complex. The measured H-Co bond length of 1.52(2) Å is significantly shorter than the previous value from electron diffraction work. Other structural parameters for this complex are reported and discussed. © 1996 American Institute of Physics.
• Kukolich, S. G., & Sickafoose, S. M. (1996). Microwave spectrum of the ¹⁵N¹⁶O-¹⁵N¹⁶O dimer. Molecular Physics, 89(6), 1659-1661.
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  Abstract: The microwave transitions for the (15NO)2 dimer were reinvestigated following a report by McKellar et al. (1995, Molecular Physics, 86, 273) of a discrepancy between a previously measured microwave transition frequency and the corresponding frequency calculated from their molecular constants. The present microwave measurements confirm the previous observation of a rotational transition at 11159·297(4) MHz, but this transition is apparently not due to the cis N-N bonded NO dimer, since a mixture of 15NO in argon gas is required for observation of the 11159·297 MHz transition. A new doublet was located at 11128·434(4) MHz and this transition is now assigned to the 303 ← 212 transition of the 15NO_15NO dimer, in agreement with predictions from the rotational constants of McKellar et al. This transition can be observed with either argon or neon as the expansion gas. New structural parameters obtained from the microwave data are in excellent agreement with those based on the FTIR data.
• Kukolich, S. G., Sickafoose, S. M., & Breckenridge, S. M. (1996). Microwave molecular structure measurements for tetracarbonyldihydroosmium, a classical dihydride. Journal of the American Chemical Society, 118(1), 205-208.
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  Abstract: Microwave rotational spectra for six isotopomers of H2Os(CO)4 were measured in the 4-12 GHz range using a Flygare-Balle-type spectrometer. The 18 rotational constants from these isotopomers were used to determine eight structural parameters describing the gas-phase structure of this complex. This near-octahedral complex has C2v symmetry and the dipole moment lies along the c-principal axis for the normal isotopomer. The distance between H atoms, obtained directly from experimental structural parameters, is rHH = 2.40(2) Å. This rather long H-H distance indicates that this is clearly a "dihydride" rather than a "dihydrogen" complex. The Os-H bond lengths are rOsH = 1.72(1) Å. The osmium-carbonyl carbon bond lengths for axial and equatorial carbonyl groups are rOsC1 = 1.96(1) Å and rOsC3 = 1.97(2) Å. Results for other structural parameters obtained using least-squares fitting and the structural parameters obtained using the Kraitchman method are presented and discussed. No evidence for internal motion was observed for this complex.
• Sickafoose, S. M., Wikrent, P., Drouin, B. J., & Kukolich, S. G. (1996). Microwave spectra and quadrupole coupling measurements for methyl rhenium trioxide. Chemical Physics Letters, 263(1-2), 191-196.
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  Abstract: Microwave rotational transitions for J′ ← J = 1 ← 0 and 2 ← 1 were measured in the 6-14 GHz range for methyl rhenium trioxide using a Flygare-Balle type, pulsed-beam spectrometer. The rotational constants for the most abundant isotopomers are B(187Re) = 3466.964(2) MHz and B(185Re) = 3467.049(3) MHz. The quadrupole coupling strengths are eQq(187Re) = 716.55(2) MHz and eQq(185Re) = 757.19(3) MHz. Transitions were also observed for 13C isotopomers and 18O isotopomers. The value for the Re-C bond length obtained from a Kraitchman analysis is R(Re-C) = 2.080 Å. The rhenium quadrupole coupling strengths are about 20% smaller than those obtained for HRe(CO)5.
• Vemulapalli, G. K., & Kukolich, S. G. (1996). Why does a stream of water deflect in an electric field?. Journal of Chemical Education, 73(9), 887-888.
• Breckenridge, S. M., & Kukolich, S. G. (1995). Precise laboratory measurements of methanol rotational transition frequencies in the 5 to 13 GHz region. Astrophysical Journal Letters, 438(1), 504-505.
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  Abstract: Rotational transitions for CH3OH were measured in the 5-13 GHz range with a precision and accuracy of a few kilohertz or less using a Flygare-Balle type pulsed-beam Fourier transform microwave spectrometer. The accurate center frequencies for transitions measured should be useful in determining accurate Doppler shifts and making positive molecule identification in radio astronomy.
• FOREMAN, P., CHIEN, K., & KUKOLICH, S. (1995). BEAM MASER MEASUREMENTS OF ROTATIONAL RELAXATION OF H2CO. JOURNAL OF CHEMICAL PHYSICS, 62(12), 4710-4714.
• Kukolich, S. G. (1995). Alternating C-C bond lengths in gas-phase (benzene)chromium tricarbonyl. Journal of the American Chemical Society, 117(20), 5512-5514.
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  Abstract: The microwave rotational spectrum of ([1,2-D2]benzene)chromium tricarbonyl was measured in the 4-12 GHz range using a Flygare-Balle-type spectrometer. This spectrum contains transitions due to two different structural isomers of this complex. These results are interpreted in terms of a reduction of the symmetry of benzene to C3v due to interactions with the Cr(CO)3 moiety. One structural isomer (isomer E) occurs when the deuterium atoms are at the ends of a "long" C-C bond, the other (isomer S), when the deuterium atoms are at the ends of a "short" C-C bond. The data indicate a difference of 0.016 Å in adjacent benzene C-C bond lengths in this complex.
• Kukolich, S. G., McKay, R. T., Breckenridge, S. M., Flores, L. D., Morris, G. E., Sickafoose, S. M., & Morrison, D. L. (1995). Measurements of microwave spectra and structural parameters for cyclopentadienylchromium dicarbonyl nitrosyl. Inorganic Chemistry, 34(16), 4182-4186.
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  Abstract: Microwave rotational spectra were measured for eight isotopomers of η5-C5H5Cr(CO)2NO using a pulsed-beam, Fourier transform spectrometer. The normal isotopomer is a near-symmetric rotor with A = 1001.693(2), B = 797.2724(6), and C = 797.0143(6) MHz. This complex has a "piano-stool" type structure, with one symmetry plane. The accidental, near-symmetric top inertia tensor gives a clear indication of different bonding and structural parameters for the nitrosyl group and the carbonyl groups, since 3-fold symmetry for the nitrosyl and carbonyl groups would result in a much larger value for B-C. The nitrosyl and carbonyl groups form different angles with the z-axis which passes through the Cr atom and center of C5H5. The C5H5-Cr-NO angle is 128°, and the C5H5-Cr-CO angle is 120°. The distance from the Cr atom to the C5H5 ring is z (Cr-C5H5) = 1.86 Å. The a-axis forms an angle of 4° with the z-axis. Other structural parameters are obtained and discussed. The C5H5 ring is oriented so that two of the cyclopentadienyl carbon atoms are staggered with respect to the NO nitrogen atom. The 14N quadrupole coupling values are eQqaa = 0.312(2) and eQqbb = -0.448(2) MHz. © 1995 American Chemical Society.
• Kukolich, S. G., McKay, R. T., Flores, L. D., & Morris, G. E. (1995). Measurements of microwave rotational transitions for cyclopentadienyltungsten dicarbonyl nitrosyl. Journal of Physical Chemistry, 99(31), 11820-11822.
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  Abstract: The microwave spectrum of (η5-C5H5)W(CO)2NO was observed using a Flygare-Balle type pulsed beam spectrometer. Fourteen a-dipole transitions in the 5-10 GHz range were measured. Rotational constants obtained are A = 952.(1) MHz, B = 708.316(2) MHz, and C = 701.857(2) MHz. Structural parameters obtained from the data analysis are r(C5H5-W) = 2.06(3) Å, ∠C5H5-W-N = 122.7(10)°, and ∠C5H5-W-CO = 123.2(10)°. The difference between the nitrosyl and carbonyl angles with respect to the C5H5 symmetry axis is much smaller for this complex than for the C5H5Cr(CO)2NO complex. © 1995 American Chemical Society.
• Mckay, R. T., Hubbard, J. L., & Kukolich, S. G. (1995). The Microwave Spectrum of Cyclopentadienyl Vanadium Tetracarbonyl, a Fluxional Molecule. Journal of Molecular Spectroscopy, 172(2), 378-383.
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  Abstract: The microwave spectrum of the symmetric-top, transition metal complex n5-C5H5V(CO)4 was measured in the 3-11 GHz range using a Flygare-Balle-type spectrometer. The molecular parameters obtained from the spectra are B = 640.429(5) MHz, eqQ(51V) = -4.77(6) MHz, and DJ = 0.17(4) kHz. Approximately one-half of the measured transition frequencies did not fit the pattern expected for a symmetric-top, rigid rotor with quadrupole coupling and are believed to be due to the effects of a low-frequency vibrational mode. In addition, the line centers for the rotational transitions which were fit to the symmetric-top model showed systematic deviations of approximately ± 20 kHz. It is proposed that these two anomalies are due to low-frequency CO bending modes which result in deviations from the C4ν symmetry of the V(CO)4 group. © 1995 Academic Press. All rights reserved.
• RICE, J., COUDERT, L., MATSUMURA, K., SUENRAM, R., LOVAS, F., STAHL, W., PAULEY, D., & KUKOLICH, S. (1995). THE ROTATIONAL AND TUNNELING SPECTRUM OF THE H2S.CO2 VANDERWAALS COMPLEX. JOURNAL OF CHEMICAL PHYSICS, 92(11), 6408-6419.
• KUKOLICH, S. (1994). HIGH-RESOLUTION MEASUREMENTS OF CL-35 AND D QUADRUPOLE COUPLING IN CH2DCL AND CD3CL. JOURNAL OF CHEMICAL PHYSICS, 55(9), 4488-&.
• Kukolich, S. G., & Sickafoose, S. M. (1994). Microwave spectrum and molecular structure for manganese pentacarbonyl hydride. Inorganic Chemistry, 33(6), 1217-1219.
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  Abstract: Microwave rotational transitions for HMn(CO)5 with 13C isotopic substitution in the axial and in one equatorial site were measured using a Flygare-Balle-type pulsed-beam spectrometer. Rotational constants obtained are A = B = 903.433(1) MHz for the axial 13CO isotopomer and A = 902.278(3) MHz and B = 907.761(3) MHz for the isotopomer with one equatorial 13C substitution. The new data are combined with previous data on HMn(CO)5 and DMn(CO)5 to obtain structural parameters for this complex. The Mn-H bond length obtained is r(Mn-H) = 1.65(2) Å and 〈Cax-Mn-Ceq = 97.0(5)°. © 1994 American Chemical Society.
• Kukolich, S. G., Sickafoose, S. M., Flores, L. D., & Breckenridge, S. M. (1994). Measurements of the microwave spectrum and structural parameters for benzene chromium tricarbonyl. The Journal of Chemical Physics, 100(9), 6125-6128.
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  Abstract: Microwave spectra for four isotopomers of benzene chromium tricarbonyl were measured in the 4-17 GHz range using a Flygare-Balle type pulsed beam spectrometer. Rotational constants obtained are B(52Cr)=732.8886(6) MHz and B(53Cr)=732.8966(3) MHz. Asymmetric top spectra were observed for a single 13C substitution on the benzene ring giving B( 13C-bz)=729.9606(3) and C(13C-bz)=727.9024(2) MHz. For a single 13C substitution on one of the carbonyl carbons B( 13CO)=731.9036(8) and C(13CO)=729.1657(8) MHz. Since no effects of possible internal rotation were observed on the 13C asymmetric top spectra, we can place a lower limit on the V6 potential for internal rotation of V6>4.0 THz (=1.6 kJ/mole). The centrifugal distortion constants are small, Dj=0.05 kHz and D JK=-0.05 kHz, indicating a fairly rigid structure. The 53Cr quadrupole coupling strength is low, eqQ(2(53Cr)=-12. 11(1) MHz, indicating a near octahedral charge distribution around the Cr atom. Structural parameters obtained are the center of the benzene chromium distance r(Cr-bz)=1.67(2) Å, the chromium-carbonyl bond length r(Cr-CO)=1.86(1) Å and the OC-Cr-CO interbond angle α=88(1)°. © 1994 American Institute of Physics.
• Palmer, S. E., Scherer, S. W., Kukolich, M., Wijsman, E. M., Tsui, L. C., Stephens, K., & Evans, J. P. (1994). Evidence for locus heterogeneity in human autosomal dominant split hand/split foot malformation. American journal of human genetics, 55(1), 21-6.
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  Split hand/split foot (SHSF; also known as ectrodactyly) is a human developmental disorder characterized by missing central digits and other distal limb malformations. An association between SHSF and cytogenetically visible rearrangements of chromosome 7 at bands q21-q22 provides compelling evidence for the location of a causative gene at this location, and the locus has been designated SHFD1. In the present study, marker loci were localized to the SHFD1 critical region through the analysis of somatic cell hybrids derived from individuals with SHSF and cytogenetic abnormalities involving the 7q21-q22 region. Combined genetic and physical data suggest that the order of markers in the SHFD1 critical region is cen-D7S492-D7S527-(D7S479-D7S491)-SHFD1-++ +D7S554-D7S518-qter. Dinucleotide repeat polymorphisms at three of these loci were used to test for linkage of SHSF to this region in a large pedigree that demonstrates autosomal dominant SHSF. Evidence against linkage of the SHSF gene to 7q21-q22 was obtained in this pedigree. Therefore, combined molecular and genetic data provide evidence for locus heterogeneity in autosomal dominant SHSF. We propose the name SHSF2 for this second locus.
• Sickafoose, S. M., Breckenridge, S. M., & Kukolich, S. G. (1994). Microwave spectra for (C₆H₅D)Cr(CO)₃, (C₆D₆)Cr(CO)₃, and (C₆H₅F)Cr(CO)₃ and the structure of (benzene)chromium tricarbonyl. Inorganic Chemistry, 33(23), 5176-5179.
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  Abstract: Microwave spectra for the D1 and D6 isotopomers of (benzene)chromium tricarbonyl and (fluorobenzene)chromium tricarbonyl were measured using a Flygare-Balle type microwave spectrometer system. The new rotational constants for the deuterium-substituted isotopomers are used with previous data which include 13C isotopomers to obtain a gas-phase structure for (benzene)chromium tricarbonyl. The new rotational constant for the C6D6, symmetric-top, isotopomer is B(bz-d6) = 698.6934(1) MHz. Asymmetric-top structure were observed for a single deuterium substitution on benzene, giving B(bz-d1) = 730.0491(4) MHz and C(bz-d1) = 723.6641(4) MHz. Rotational constants obtained for (fluorobenzene)chromium tricarbonyl are A = 814.1491(2) MHz, B = 641.1594(2) MHz, and C = 586.5866(1) MHx. The centrifugal distortion constants are small, with DJ ≅ 0.05 kHz. Structural parameters determined are center of the benzene carbon plane to chromium distance r(Cr-bz) = 1.66(2) Å, the chromium to carbonyl carbon bond length r(Cr-CO ) = 1.876(7) Å, the benzene carbon to hydrogen bond length r(C-H) = 1.080(3) Å, and the carbonyl carbon to oxygen bond length r(C-O) = 1.148(7) Å. The OC-Cr-CO interbond angle is α = 87.4(6)°. The average benzene C-C bond length is 1.413(4) Å. A small isotopic shift in the 53Cr quadrupole coupling strength was observed for the C6D6 isotopomer relative to the normal isotopomer. The hydrogen atoms are displaced out of the benzene carbon plane toward the Cr atom with the C-H bond axis at an angle γ = 2.8(2)° with respect to the benzene carbon plane. © 1994 American Chemical Society.
• KUKOLICH, S. (1993). MEASUREMENTS OF DEUTERIUM QUADRUPOLE COUPLING IN FORMIC ACID. JOURNAL OF CHEMICAL PHYSICS, 51(1), 358-&.
• KUKOLICH, S., BUMGARNER, R., & PAULEY, D. (1993). THE MICROWAVE-SPECTRUM OF THE ONN-HF COMPLEX. CHEMICAL PHYSICS LETTERS, 141(1-2), 12-15.
• Kukolich, S. G., & Sickafoose, S. M. (1993). Measurements of the microwave spectrum, Re-H bond length, and Re quadrupole coupling for HRe(CO)₅. The Journal of Chemical Physics, 99(9), 6465-6469.
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  Abstract: Rotational transition frequencies for rhenium pentacarbonyl hydride were measured in the 4-10 GHz range using a Flygare-Balle type microwave spectrometer. The rotational constants and Re nuclear quadrupole coupling constants for the four isotopomers, (1) H187Re(CO)5, (2) H185Re(CO)5, (3) D187Re(CO)5, and (4) D185Re(CO)5, were obtained from the spectra. For the most common isotopomer, B(1) = 818.5464(2) MHz and eq Q(187Re) = -900.13(3) MHz. The Re-H bond length (r0) determined by fitting the rotational constants is 1.80(1) Å. Although the Re atom is located at a site of near-octahedral symmetry, the quadrupole coupling is large due to the large Re nuclear moments. A 2.7% increase in Re quadrupole coupling was observed for D-substituted isotopomers, giving a rather large isotope effect on the quadrupole coupling. The Cax-Re-Ceq angle is 96(1)°, when all Re-C-O angles are constrained to 180°. © 1993 American Institute of Physics.
• Kukolich, S. G., & Sickafoose, S. M. (1993). The microwave spectrum and MnH bond length for HMn(CO)₅. Chemical Physics Letters, 215(1-3), 168-172.
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  Abstract: The microwave rotational spectrum for the symmetric top, manganese pentacarbonylhydride, was measured in the 5-11 GHz range using a pulsed-beam, Fourier transform microwave spectrometer. For HMn(CO)5 we obtained A = B = 907.9841 (2) MHz and eqQ(MN) = -144.22(2) MHz. For DMn(CO)5, A = B = 902.7682(3) MHz and eqQ(Mn) = -45.24(4) MHz. Only K = 0 and K = 4 transitions were observed, confirming the expected C4v symmetry. With other structural parameters constrained to previously reported values, r0(MnH) = 1.64(4) Å. The CaxMnCeq angle derived from the data is approximately 97°C, if MnCO angles are constrained to 180°C. © 1993.
• Kukolich, S. G., Roehrig, M. A., Wallace, D. W., & Henderson, G. L. (1993). Microwave measurements of the rotational spectrum and structure of (Butadiene)iron tricarbonyl. Journal of the American Chemical Society, 115(5), 2021-2027.
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  Abstract: The rotational spectra of 10 isotopomers of (butadiene)iron tricarbonyl were measured using a Flygare-Balle-type microwave spectrometer operating in the 5-17-GHz frequency range. The 30 measured rotational constants were used to determine 12 gas-phase structural parameters describing the cis-butadiene conformation and the locations and orientations of the butadiene and CO ligands relative to the iron atom. Kraitchman analyses of these microwave measurements, with single and multiple deuterium substitution, provide accurate data on the hydrogen atom coordinates in the complex. The terminal CH2 groups of butadiene are found to be rotated by 28° out of the butadiene plane, and the CH2 plane is folded away from the C1-C2 axis by 27° in a direction away from the iron atom. Least-squares fits to all rotational constants to determine structural parameters were also carried out, and the results are compared with coordinates from the Kraitchman method. Other structural parameters are compared with X-ray diffraction results on similar compounds. The four possible single-substitution 13C isotopomers were observed in natural abundance samples. Samples for the two D1, two D3, and D4 substitutions on terminal H atoms were synthesized. Proton NMR spectra were analyzed to obtain improved chemical shifts and coupling constants for this complex.
• Kukolich, S. G., Wallace, D. W., Wickwire, D. M., Sickafoose, S. M., & Roehrig, M. A. (1993). The microwave spectrum and molecular structure for Fe(NO)₂(CO)₂. Journal of Physical Chemistry, 97(37), 9317-9322.
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  Abstract: Microwave spectra for five isotopomers of iron dinitrosyl dicarbonyl were measured in the 4-16-GHz range using a Flygare-Balle type spectrometer. Numerous b-dipole transitions were observed for Fe(NO)2(CO)2, Fe15NONO(CO)2, Fe(15NO)2(CO)2, Fe(15NO)213COCO, and 54Fe(15NO)2(CO)2. Measured rotational constants were analyzed to obtain an accurate gas-phase structure. Some of the structural parameters obtained are ZN-Fe-N = 121(2)°, 〈C-Fe-C = 101(2)°, r(Fe-N) = 1.69(2) Å, r(Fe-C) = 1.85(2) Å, 〈Fe-N-O = 176(2)°, and 〈Fe-C-O = 177(2)°. NMR and IR data are also given. Nitrogen quadrupole coupling tensors were obtained from hyperfine structure on transitions for Fe(14NO)2(CO)2 and Fe(14NO)(15NO)(CO)2. The z principal axis for the quadrupole tensor is rotated 62° away from the Fe-N bond direction and principal axis components are eQqzz = -1.5 MHz, eQqxx = 1.0 MHz and eQqyy = 0.53 MHz. © 1993 American Chemical Society.
• Henderson, G. L., Roehrig, M. A., Wikrent, P., & Kukolich, S. G. (1992). Microwave spectrum and structural parameters of iron tricarbonyl 1,3-cyclohexadiene. Journal of Physical Chemistry, 96(21), 8303-8306.
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  Abstract: A total of 90 a- and c-dipole rotational transitions were measured in the 5-14-GHz range for 56Fe(CO)3(1,3-cyclohexadiene) and 54Fe(CO)3(1,3-cyclohexadiene), using a Flygare-Balle type pulsed-beam Fourier transform spectrometer. Spectroscopic constants A, B, C, ΔJ, ΔJK, δJ, and δK were obtained for both isotopomers using a Watson type distortable rotor Hamiltonian. The rotational constants obtained for 56Fe(CO)3(1,3-cyclohexadiene) are A = 960.0298 (4), B = 681.8343 (2), and C = 659.3087 (2) MHz. Six rotational constants were used to determine three structural parameters describing the relative orientation of the cyclohexadiene and carbonyl ligands. © 1992 American Chemical Society.
• Kukolich, S. G., Roehrig, M. A., Henderson, G. L., Wallace, D. W., & Chen, Q. (1992). Microwave measurements of the rotational spectrum of butadiene iron tricarbonyl. The Journal of Chemical Physics, 97(2), 829-831.
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  Abstract: The rotational spectrum of butadiene iron tricarbonyl was measured using a Flygare-Balle type microwave spectrometer. A total of 71 a-dipole and c-dipole transitions in the 5-17 GHz range were obtained for this asymmetric top transition metal complex. The "best fit" rotational constants are A = 1005.4201(3) MHz, B = 958.0408(2) MHz, and C = 933.6865(3) MHz. Centrifugal distortion constants were also obtained in the least-squares fit to the measured transitions. The present measurements indicate an upper limit of 40 kHz for splittings due to internal rotation, which places a lower limit on the barrier height of V3 ≥ 1.2 THz. The measured rotational constants are used to determine CO bond angles and the distances between Fe and the butadiene C atoms. © 1992 American Institute of Physics.
• Lax, D., & Kukolich, S. G. (1992). Generation of furazolidone radical anion and its inhibition by glutathione. Biochemical Medicine and Metabolic Biology, 48(1), 56-63.
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  PMID: 1326300;Abstract: Furazolidone is a nitrofuran drug which causes dilated cardiomyopathy in turkeys and serves as an important model of human dilated cardiomyopathy. Although extensively investigated, the chemical mechanism by which furazolidone produces injury remains unknown. In this work we used electron paramagnetic resonance (EPR) spectroscopy to show that furazolidone was reduced to its corresponding nitro anion radical by ascorbate and hypoxanthine. Glutathione prevented the generation of this anion radical. These results document directly, with EPR spectroscopy, the presence of furazolidone anion radical during biochemical reduction and suggest a protective role of glutathione in furazolidone-induced injury. These data enhance our understanding of furazolidone metabolism and may be useful in defining its role in furazolidone-induced dilated cardiomyopathy. © 1992.
• Lax, D., & Kukolich, S. G. (1992). Generation of furazolidone radical anion and its inhibition by glutathione. Biochemical medicine and metabolic biology, 48(1), 56-63.
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  Furazolidone is a nitrofuran drug which causes dilated cardiomyopathy in turkeys and serves as an important model of human dilated cardiomyopathy. Although extensively investigated, the chemical mechanism by which furazolidone produces injury remains unknown. In this work we used electron paramagnetic resonance (EPR) spectroscopy to show that furazolidone was reduced to its corresponding nitro anion radical by ascorbate and hypoxanthine. Glutathione prevented the generation of this anion radical. These results document directly, with EPR spectroscopy, the presence of furazolidone anion radical during biochemical reduction and suggest a protective role of glutathione in furazolidone-induced injury. These data enhance our understanding of furazolidone metabolism and may be useful in defining its role in furazolidone-induced dilated cardiomyopathy.
• RUBEN, D., & KUKOLICH, S. (1992). DEUTERIUM QUADRUPOLE COUPLING IN FORMIC-ACID. JOURNAL OF CHEMICAL PHYSICS, 60(1), 100-102.
• Roehrig, M. A., & Kukolich, S. G. (1992). The microwave spectrum and structure for the HCCHCO complex. Chemical Physics Letters, 188(3-4), 232-236.
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  Abstract: Rotational transitions were measured for five isotopomers of HCCHCO using a Flygare-Balle type microwave spectrometer. The observed spectrum is consistent with a linear, hydrogen-bonded HCCHCO structure. Measured rotational constants in MHz, are B = 1397.370(1) for HCCOCO, 1394.963(1) for HCCDCO, 1385.142(1) for HCCHCO, 1331.23(1) for DCCHCO and 1329.684(2) for DCCDCO. The measured rotational constants were fit to obtain a center-of-mass separation for HCCHCO of R*c.m. = 5.018(7) Å. Distortion constants were obtained and analyzed to obtain a force constant and estimate the dissociation energy. © 1992.
• Roehrig, M. A., Wallace, D. W., & Kukolich, S. G. (1992). Microwave measurements of manganese quadrupole coupling in cyclopentadienyl manganese tricarbonyl. The Journal of Chemical Physics, 96(4), 2449-2452.
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  Abstract: Microwave measurements of rotational transitions in cyclopentadienyl manganese tricarbonyl were made using a Flygare-Balle type pulsed beam Fourier transform microwave spectrometer operating in the 4-14 GHz range. Ninety-six hyperfine transitions were assigned for this prolate symmetric top for the rotational transitions J = 2→ 3, 3→4, 4→5, 5→6, and 6→7. Molecular constants obtained from the analysis of the spectrum are B = 828.0333(6) MHz, DJ = 0.088(9) kHz, DJK= -0.04(3) kHz, eQqαα(Mn) = 68.00(4) MHz, Cbb(Mn) = -5.5(8) kHz. The distortion parameter DJ for CpMn(CO)3 is compared to other DJ values for similar type transition metal complexes. © 1992 American Institute of Physics.
• Roehrig, M. A., Wikrent, P., Huber, S. R., Wigley, D. E., & Kukolich, S. G. (1992). The microwave spectrum of cyclobutadiene iron tricarbonyl. Journal of Molecular Spectroscopy, 154(2), 355-360.
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  Abstract: The rotational spectrum of cyclobutadiene iron tricarbonyl was measured using a Flygare-Balle-type microwave spectrometer. Twenty a-dipole transitions were measured in the 5-16 GHz range for this prolate symmetric-top molecule. A least-squares fit of the data to a distortable symmetric top Hamiltonian yielded B = 961.9856(8) MHz, DJ = 0.184(8) kHz, DJK = 1.20(3) kHz. These results indicate that the vibrationally averaged structure of the cyclobutadiene ring is square and perpendicular to the a-molecular axis. © 1992.
• BUMGARNER, R., PAULEY, D., & KUKOLICH, S. (1991). MICROWAVE-SPECTRA AND STRUCTURE FOR SO2...H2S, SO2...HDS, AND SO2...D2S COMPLEXES. JOURNAL OF CHEMICAL PHYSICS, 87(7), 3749-3752.
• Choe, J., Rho, Y., Lee, S., Floch, A. L., & Kukolich, S. G. (1991). Fourier transform spectroscopy of the CS d³Δ_i-a³Π_r system: Indirect measurement of the ¹Σ^- valence state. Journal of Molecular Spectroscopy, 149(1), 185-213.
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  Abstract: The electronic emission spectrum of CS in the range of 9500-17500 cm-1 was recorded with 0.03 cm-1 resolution using the 1-m Fourier transform spectrometer associated with the McMath solar telescope at Kitt Peak National Observatory, Arizona, with an electric discharge in a CS2 and helium mixture. A total of more than 3400 transition frequencies for 24 d3Δ1 (v = 3-14)-a3Π0 (v = 0-2), d3Δ2 (v = 3-12)-a3Π1 (v = 0-2), and d3Δ3 (v = 3-9)-a3Π2 (v = 0-2) bands have been assigned for the vibronic structure of the near-infrared electronic emission. Thirteen of these bands were observed for the first time. The study of the Λ-doubling perturbation of the d3Δ1-a3Π0 (7-0) band allowed us to locate a vibrational level of the previously unknown 1Σ- valence state of CS (T = 40 835.5 cm-1, B = 0.597 cm-1). © 1991.
• KUKOLICH, S. (1991). PROTON MAGNETIC SHIELDING TENSORS FROM SPIN-ROTATION MEASUREMENTS ON H2CO AND NH3. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 97(20), 5704-5707.
• KUKOLICH, S., & PAULEY, D. (1991). CENTRIFUGAL-DISTORTION ANALYSIS FOR THE BENT ISOMER OF N2O-HF. CHEMICAL PHYSICS, 131(2-3), 403-408.
• Kukolich, S. G., & Huffman, D. R. (1991). EPR spectra of C₆₀ anion and cation radicals. Chemical Physics Letters, 182(3-4), 263-265.
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  Abstract: EPR spectra of dilute solutions of cation and anion radicals produced from a nearly pure C60 sample and samples containing C60 and C70 were recorded at 9.1 GHz, near 3400 G. The measured g-value, which assigned to (C60)+, is 2.0030(2). A series of four resonances were observed for the anion radicals. The measured g-values are 2.0002(4), 2.0006(2), 2.0009(4) and 2.0014(4). For most cases, narrow resonances with linewidth of 0.2 G or less were obtained with no apparent hyperfine structure. Three of the anion g-values are tentatively assigned to: (C60)- at g=2.0006, (C60)3- at g=2.0009 and (C60)5- at g=2.0014. © 1991.
• Kukolich, S. G., Roehrig, M. A., Haubrich, S. T., & Shea, J. A. (1991). Microwave measurements of cobalt and nitrogen quadrupole coupling in Co(CO)₃NO. The Journal of Chemical Physics, 94(1), 191-194.
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  Abstract: J = 2→3, 3→4, 4→5, and 5→6 transitions in the oblate symmetric top molecule cobalt tricarbonyl nitrosyl were measured using a Flygare-Balle type pulsed beam microwave spectrometer. K = 0 and K = 3 transitions were observed for J = 3→4 and 4→5. Hyperfine structure due to 59Co and 14N nuclear quadrupole coupling interactions was well resolved. The measured quadrupole coupling strengths are eQq cc. (59Co) = 35.14(30) MHz and eQqcc ( 14N) = -1.59(10). Measured rotation and distortion constants are B0 = 1042.1590(4) MHz and Dj = 0.17(8) kHz. The measured B value is 4% smaller than the B value calculated from electron diffraction data. Spin-rotation and a quadrupole distortion term were also obtained for 59Co. © 1991 American Institute of Physics.
• Kukolich, S. G., Roehrig, M. A., Haubrich, S. T., & Shea, J. C. (1991). Erratum: Microwave measurements of cobalt and nitrogen quadrupole coupling in Co(CO)₃NO (Journal of Chemical Physics (1991) 94 (191)). The Journal of Chemical Physics, 94(9), 6338-.
• Roehrig, M. A., Chen, Q., Haubrich, S. T., & Kukolich, S. G. (1991). Microwave measurements of the rotational spectrum for cyclopentadienyl-cobalt dicarbonyl. Chemical Physics Letters, 183(1-2), 84-88.
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  Abstract: Rotational transitions in the 6-18 GHz range were measured for cyclopentadienyl-cobalt dicarbonyl (CpCo(CO)2) using a Flygare-Balle type pulsed beam spectrometer. Splitting and additional transitions due to hindered internal rotation and cobalt quadrupole coupling were observed in the spectrum. Analysis of the spectrum provided the rotational constants A=1625(20), B=1257(2) and C=876(2) MHz. This molecule appears to have a tenfold barrier to rotation of the -Co(CO)2 fragment about the C5 axis of the Cp group. The potential energy barrier to internal rotation is V10=0.82(20) THz (0.3 kJ/mol). The value of the OCCoCO angle was found to be θ=98(5)°. This and other structure parameters will be compared with electron diffraction results. The 59Co quadrupole coupling components are eQqaa=12(4) MHz and eQqbb=132(4) MHz. © 1991.
• Combariza, J., Salzman, W. R., & Kukolich, S. G. (1990). NH₃ and PH₃ molecular quadrupole moments and the signs of molecular g-values. Chemical Physics Letters, 167(6), 607-608.
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  Abstract: Molecular Zeeman effect data for NH3 and PH3 was reviewed and reanalyzed to obtain molecular quadrupole moments. Since the signs of molecular g-values were not directly measured, molecular quadrupole moments were also calculated using ab initio SCF programs to remove ambiguities in the signs of g-values. For NH3, Qcc (measured) = -3.4(4) buckingham and Qcc (calculated) = -2.8 buckingham. For PH3, Qcc (measured) = -2.3(12) buckingham and Qcc (calculated) = -2.4 buckingham. These values support positive g-values for NH3 (gaa=gbb=0.568(2), gcc=0.500(2)), and for PH3 gaa=gbb=-0.325(9), and gcc=0.011(1). © 1990.
• Haubrich, S. T., Roehrig, M. A., & Kukolich, S. G. (1990). Structure and quadrupole coupling measurements on ClF₃. The Journal of Chemical Physics, 93(1), 121-125.
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  Abstract: Seventy-nine new microwave transitions for 35ClF3 and 37ClF3 in the 6-18 GHz range were measured using a Flygare-Balle-type spectrometer. Rotational transition frequencies were used to obtain "effective" structure parameters for the ground vibrational state zCl-F (along C2 axis) = 1.5985(4) Å, r Cl-F = 1.700 73(5) Å and ΘF-Cl-F = 87.48(4)°. Analysis of hyperfine structure due to chlorine quadrupole coupling and observed transition frequencies yield the following molecular parameters for 35ClF3: A = 13 748.25(1) MHz, B = 4611.719(2) MHz, C = 3448.629(3) MHz, eQqaa = 82.03(3) MHz, and eQqbb = 65.35(2) MHz. Molecular parameters obtained for 37ClF3 are: A = 13 653.54(1) MHz, B = 4611.866(2) MHz, C = 3442.719(4) MHz, eQqaa = 64.66(4) MHz, and eQqbb = 51.53(3) MHz. © 1990 American Institute of Physics.
• Kukolich, S. G., & Pauley, D. J. (1990). Comment on: Structure of H₂S-SO₂. The Journal of Chemical Physics, 93(1), 871-872.
• Kukolich, S. G., & Pauley, D. J. (1990). Erratum: The rotational spectra and centrifugal distortion parameters for the NNO-DF and ONN-DF complexes (Journal of Chemical Physics (1989) 90 (3458)). The Journal of Chemical Physics, 93(2), 1487-1488.
• Kukolich, S., McCarthy, M., & Thaddeus, P. (1990). Molecular structure of o-benzyne from microwave measurements. JOURNAL OF PHYSICAL CHEMISTRY A, 108(14), 2645-2651.
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  The o-benzyne molecule has been known for many years to be an important, but short-lived,, reaction intermediate in substitution reactions and more recently in cyclization reactions of enediynes. Although there has been widespread interest in this transient molecule, previous experimental structural data were very limited. In the present work, rotational transitions for o-benzyne were measured with a pulsed-beam, Fourier transform microwave spectrometer for all unique, singly substituted C-13 and single-D isotopomers. The o-benzyne was efficiently produced by flowing a dilute mixture of isotopically enriched benzene in neon through a pulsed-DC discharge beam source. The new data, combined with previous data for the normal isotopomer, provide a complete set of structural parameters for this molecule. The r(s) substitution coordinates and the coordinates from a least-squares fit are reported and are in good agreement. When using the least-squares fit to obtain structural parameters, correction terms arising from harmonic terms in the vibrational averaging were subtracted from the measured rotational constants to obtain a better representation of the planar equilibrium structure. Further improvements in the fits were obtained by applying small, mass-dependent adjustments to the atom coordinates. Structural parameters obtained from the fit to these modified rotational constants are an acetylenic C(1)equivalent toC(2) bond length of 1.264(3) Angstrom, and the other bond lengths C-2-C-3 1.390(3) Angstrom, C-3-C-4 = 1.403(3) Angstrom, C-4-C-5 = 1.404(3) Angstrom, C-3-H-1 = 1.095(9) Angstrom, and C-4-H-2 = 1.099(4) The C(1)equivalent toC(2) bond is only 0.057 Angstrom longer than the free acetylene bond. The other C-C bond lengths are within 0.01 Angstrom of those of benzene C-C bonds. New spectral data for the single-D isotopomers were used to obtain better values for the deuterium quadrupole coupling. Bond-axis deuterium quadrupole coupling constants are eQq(zz)(D-1) = 188(2) kHz, and eQq(zz)(D-2) = 185(10) kHz, which agree well with the value for benzene-D-1. The new structural parameters are compared here with theoretical parameters and with an NMR measurement of the C-1-C-2 bond length.
• Pauley, D. J., & Kukolich, S. G. (1990). Microwave spectra and structures of the NNO-HCN, ¹⁵NNO-HCN, and NNO-DCN complexes. The Journal of Chemical Physics, 93(6), 3881-3886.
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  Abstract: A total of 60 a- and b-dipole rotational transitions were measured in the 4-18 GHz range for the NNO-HCN, 15NNO-HCN, and NNO-DCN bimolecular complexes using a pulsed-beam, Fourier transform microwave spectrometer. Spectroscopic constants (A - DK), B, C, DJ, D JK, eQqaa (N of HCN), and eQqbb (N of HCN) were obtained by fitting the observed transition frequencies with a first-order quadrupole coupling interaction Hamiltonian. The structure of the complex appears to be planar with NNO and NCH nearly parallel. It can be described with the distance Rcm between the center-of-masses of the monomer subunits, the angle θ between HCN and Rcm, and the angle φ between N2O and Rcm. A least-squares fit to the nine rotational constants to obtain the structure parameters Rcm, θ, and φ, produced three local minimia for bent structures with standard deviations of < 25 MHz. A Kraitchman analysis was used to determine magnitudes of principal axes coordinates for the N of HCN, and the terminal N of NNO. The best nonlinear least-squares fit result (structure I, lowest standard deviation of the fit = 7.2 MHz) produced the best match to the coordinates from the Kraitchman analysis. The spectroscopic constants B, C, and eQqaa were used in a second structural analysis to determine values for R cm, θ, and φ. These results were compared with the above coordinates. The best least-squares fit structure parameters for the vibrationally averaged structure are Rcm = 3.253(4) Å, θ = 89.1 (5.4)°, and φ = 76.4(0.4)°. Comparisons are made with other similar weakly bound complexes. © 1990 American Institute of Physics.
• Pauley, D. J., Roehrig, M. A., & Kukolich, S. G. (1990). Rotational transition and quadrupole coupling measurements on the NNO-HCN complex. Chemical Physics Letters, 167(1-2), 57-61.
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  Abstract: Seven a-dipole and seven b-dipole transitions were measured for one isomer of the NNO-HCN complex using a pulsed-beam, Fourier transform microwave spectrometer. Rotational constants A+ΔK=10326.3(4) MHz, B=2814.32(14) MHz and C=2201.00(12) MHz and distortion constants ΔJ=0.014(8) MHz and ΔJK=0.14(6) MHz were obtained by fitting the observed transition frequencies. A quadrupole coupling strength due to the HCN nitrogen of eQqaa=1.97±0.05 MHz was obtained by fitting low-J transitions. Approximate structural parameters are obtained using moments of inertia and quadrupole coupling data. © 1990.
• Rice, J. K., Coudert, L. H., Matsumura, K., Suenram, R. D., Lovas, F. J., Stahl, W., Pauley, D. J., & Kukolich, S. G. (1990). The rotational and tunneling spectrum of the H₂S·CO ₂ van der Waals complex. The Journal of Chemical Physics, 92(11), 6408-6419.
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  Abstract: The rotational spectra of H2S·CO2 and two deuterated forms have been observed using a pulsed-beam Fourier-transform microwave spectrometer. For each of the three complexes we assign a-type and c-type transitions which are split into a "weak" and a "strong" intensity component. The analysis based on that previously used for the (H2O)2 complex and modified for application to H2S·CO2, allowed us to assign internal rotation, inversion tunneling states of the H2S and CO2 units in the complex. The following rotational constants were determined for the ground tunneling state of each species: for H2S·CO2, A = 11 048.0(26) MHz, B = 2147.786(4) MHz, and C = 1806.468(4) MHz; for HDSCO 2, A = 10 769(35) MHz, B = 2107.26(24) MHz, and C= 1775.83(24) MHz; and for D2S·CO2, A = 10 356.2(28) MHz, B = 2065.376(8) MHz, and C = 1746.122(8) MHz. The electric dipole moments were determined for the H2S·CO2 and D 2SCO2 species, resulting in the values μu = 0.410(14) D and μc = 0.822 (10) D for the H2S· CO2 species. The structure of the complex has the CO2 and the S atom of H2S in a T-shaped configuration. The H2S plane is nearly orthogonal to the CO2-S plane with an angle of about 92° and the H2S·CO2 center-of-mass separation Rc.m. is 3.498(3) Å. © 1990 American Institute of Physics.
• Shea, J. C., & Kukolich, S. G. (1990). Quadrupole coupling measurements on IF₅. Chemical Physics Letters, 168(5), 489-492.
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  Abstract: High resolution spectra of J=0→1, 1→2 and 2→3 rotational transitions in IF5 were obtained using a Flygare-Balle-type microwave spectrometer. Twenty-two transitions with K=0 or K=1 were fit to obtain the molecular parameters A0=B0=2727.4231 (8) MHz, eqccQ=1069.41 (4) and the spin-rotation interaction CC=0.016(1) MHz. © 1990.
• CASLETON, K., & KUKOLICH, S. (1989). BEAM MASER MEASUREMENTS OF HYPERFINE-STRUCTURE IN N-14(2)O. JOURNAL OF CHEMICAL PHYSICS, 62(7), 2696-2699.
• Choe, J., Lee, D., Floch, A. L., & Kukolich, S. G. (1989). Fourier transform spectroscopy of CO intercombination bands. Journal of Molecular Spectroscopy, 136(1), 173-184.
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  Abstract: Several bands of CO intercombination systems have been recorded for the first time under high-resolution Fourier transform spectroscopy: B1Σ+-e3Σ-(0-1), B1Σ+-d3Δi(0-5), and B1Σ+-d3Δi(0-12), B1Σ+-a′3Σ+(0-14), and B1Σ+-a′3Σ+(0-17). The emission spectrum was produced from an electric discharge through a mixture of formic acid and helium. Observed wavenumbers of rotational lines (0 < J < 19) are presented. The line position uncertainties range from 0.001 to 0.02 cm-1, depending on the transition intensity. These bands are forbidden by electric-dipole selection rules and borrow intensity from the main Angstrom B1Σ+-A1Π system, via spin-orbit interactions. It is shown that these data are consistent with recent studies of perturbations arising in the A1Π levels. In addition, the mixing coefficients, which represent the fractional A1Π character of each line, are also reported. © 1989.
• Kukolich, S. G., & Pauley, D. J. (1989). Centrifugal distortion analysis for the bent isomer of N₂OHF. Chemical Physics, 131(2-3), 403-408.
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  Abstract: Six previously unobserved lines for the bent form of NNO-HF (O...H hydrogen bonded) were measured using a pulsed-beam, Fourier-transform spectrometer. These lines, together with earlier data, were fitted to obtain the rotational constants and a limited set of quartic distortion constants using a Watson-type Hamiltonian in the Ir representation. The results of the fit are: A+Δ K=26322.32(32) MHz, B=2720.93(10) MHz, C=2438.72 (10) MHz, ΔJ=60.3(11) kHz, ΔJK=-3.077(15) MHz, δJ= 13.1(10) kHz and δK= 314 (47) kHz. The errors in line frequencies calculated with this extended set of parameters are two orders of magnitude smaller than errors obtained using only rigid rotor parameters. The vibrationally averaged structure and force constants for the Rc.m. stretching vibration and an in-plane-bending vibration were calculated using the rotational constants and distortion constants. It was found that ΔJ (or DJ) depends primarily on fRR-1, so that earlier analyses involvi ΔJ or DJ were reasonably accurate. © 1989.
• Kukolich, S. G., & Pauley, D. J. (1989). The rotational spectra and centrifugal distortion parameters for the NNO-DF and ONN-DF complexes. The Journal of Chemical Physics, 90(7), 3458-3462.
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  Abstract: Microwave measurements of rotational transitions for the linear ONN-DF and bent NNO-DF complexes were made using a pulsed-beam, Fourier transform spectrometer. For ONN-DF, B = 1808.959(2) MHz and DJ = 2.79(6) kHz. Structure parameters are obtained and compared with ONN-HF parameters. For the bent NNO-DF isomer, seven new transitions and previous data were fit to obtain (A + ΔK) = 25 988.4(3) MHz, B = 2701.1(2) MHz, C = 2422.3(2) MHz, ΔJ = 0.052(3) MHz, ΔJK = - 2.57(1) MHz, δJ = 0.010(5) MHz, and δK = 0.24(10) MHz. The centrifugal distortion constants for NNO-DF are used to obtain force field parameters fRR and fθθ describing motion of the DF center of mass relative to the NNO center of mass. The excellent agreement between these parameters and previous data on NNO-HF supports the simplified model used to describe the centrifugal distortion of this complex. © 1989 American Institute of Physics.
• RUBEN, D., KUKOLICH, S., HACKEL, L., YOUMANS, D., & EZEKIEL, S. (1989). LASER-MOLECULAR BEAM MEASUREMENT OF HYPERFINE-STRUCTURE IN I2 SPECTRUM. CHEMICAL PHYSICS LETTERS, 22(2), 326-330.
• Bumgarner, R. E., Choe, J., Kukolich, S. G., & Butcher, R. J. (1988). High-resolution spectroscopy of the ν₆ and ν₈ bands of formic acid. Journal of Molecular Spectroscopy, 132(1), 261-276.
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  Abstract: The ν6 and ν8 bands of formic acid at 1104.8 and 1033.5 cm-1 were observed at 0.01 cm-1 resolution using the Kitt Peak Fourier-transform spectrometer. The ν8 Q branch was observed at 0.001 cm-1 resolution using a diode laser source. These data, together with previous laser saturation, and far-IR and microwave data have been fit with a Watson A-reduced Hamiltonian to determine excited state constants. The A-type Coriolis term was included in the fit and the total Hamiltonian was diagonalized. The new data and fit improve the accuracies of the molecular constants and allow several previously undetermined hextic distortion constants in ν8 to be obtained. We have assigned several previously unassigned far-IR laser transitions occurring between rotational levels in vibrationally excited formic acid states. The new set of constants should allow accurate assignment and prediction of other formic acid far-IR laser transitions. © 1988.
• Bumgarner, R. E., Pauley, D. J., & Kukolich, S. G. (1988). Microwave measurements on ArH₂S, ArHDS and ArD₂S complexes. Journal of Molecular Structure, 190(C), 163-171.
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  Abstract: Recent work on the H2OSO2 complex revealed several previously unmeasured ArH2S transitions. In this work, microwave transitions for ArHsS, ArHDS and ArD2S complexes are reported and a structure analysis is presented. The observation of the new set of transitions assigned to a second ArHDS isomer indicates that the hydrogens of H2S are not rapidly exchanging H for D through internal rotation. The complex is unusual in that quite large differences in the vibrationally averaged structures are seen on isotopic substitution. The apparent presence in such weakly-bound complexes of several coupled modes with large amplitude vibrations causes difficulties in obtaining a single accurate equilibrium structure. © 1988.
• Kukolich, S. G., Rund, J. V., Pauley, D. J., & Bumgarner, R. E. (1988). Nitrogen quadrupole coupling in cyclopentadienylnickel nitrosyl. Journal of the American Chemical Society, 110(22), 7356-7357.
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  Abstract: High-resolution rotational spectra of C5H558Ni14N16O were obtained with a Flygare-Balle type pulsed-beam microwave spectrometer. Quadrupole hyperfine structure was clearly resolved for J = 1 → 2, 2 → 3, 3 → 4, and 4 → 5 transitions involving K = 0, 1, 2, 3, and 4 states. A nitrogen quadrupole coupling strength of eqQ = -1.216 (11) MHz and rotational constant B = 1259.2743 (8) MHz were obtained by fitting the observed spectra. DJK and DJ were also obtained from fitting the spectra. This appears to be the first gas-phase, microwave measurement of nitrogen quadrupole coupling in a transition-metal complex. The quadrupole coupling strength is compared with values for other molecules and complexes containing the NO group. © 1988 American Chemical Society.
• ROEHRIG, M., CHEN, Q., HAUBRICH, S., & KUKOLICH, S. (1988). MICROWAVE MEASUREMENTS OF THE ROTATIONAL SPECTRUM FOR CYCLOPENTADIENYL COBALT DICARBONYL. CHEMICAL PHYSICS LETTERS, 183(1-2), 84-88.
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  Rotational transitions in the 6-18 GHz range were measured for cyclopentadienyl-cobalt dicarbonyl (CpCo(CO)2) using a Flygare-Balle type pulsed beam spectrometer. Splitting and additional transitions due to hindered internal rotation and cobalt quadrupole coupling were observed in the spectrum. Analysis of the spectrum provided the rotational constants A = 1625(20), B = 1257(2) and C = 876(2) MHz. This molecule appears to have a tenfold barrier to rotation of the -Co(CO)2 fragment about the C5 axis of the Cp group. The potential energy barrier to internal rotation is V10 = 0.82(20) THz (0.3 kJ/mol). The value of the OC-Co-CO angle was found to be theta = 98(5)-degrees. This and other structure parameters will be compared with electron diffraction results. The Co-59 quadrupole coupling components are eQq(aa) = 12(4) MHz and eQq(bb) = 132(4) MHz.
• ALDRICH, P., KUKOLICH, S., CAMPBELL, E., & READ, W. (1987). MAGNETIC-SUSCEPTIBILITY ANISOTROPY, MOLECULAR G-VALUES, AND OTHER MOLECULAR-PROPERTIES OF CYCLOPROPANE AS DETERMINED FROM ROTATIONAL ZEEMAN STUDIES OF THE CYCLOPROPANE-H35CL AND CYCLOPROPANE-HC15N COMPLEXES. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 105(17), 5569-5576.
• BRECKENRIDGE, S., & KUKOLICH, S. (1987). PRECISE LABORATORY MEASUREMENTS OF METHANOL ROTATIONAL TRANSITION FREQUENCIES IN THE 5-GHZ TO 13-GHZ REGION. ASTROPHYSICAL JOURNAL, 438(1), 504-505.
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  Rotational transitions for CH3OH were measured in the 5-13 GHz range with a precision and accuracy of a few kilohertz or less using a Flygare-Balle type pulsed-beam Fourier transform microwave spectrometer. The accurate center frequencies for transitions measured should be useful in determining accurate Doppler shifts and making positive molecule identification in radio astronomy.
• Bumgamer, R. E., & Kukolich, S. G. (1987). Microwave spectra and structure of HI-HF complexes. The Journal of Chemical Physics, 86(3), 1083-1089.
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  Abstract: Microwave spectra for the HI-HF, HI-DF, DI-HF, and DI-DF complexes were measured using a pulsed-beam, Fourier-transform microwave spectrometer. Rotational transitional transitions were measured over the 4-18 GHz range to an accuracy of 5 kHz. The spectroscopic constants obtained by fitting the observed transitions for the series HI-HF, HI-DF, DI-HF, and DI-DF are, respectively: (B+C)/2=2220.7482(8), 2173.236(2), 2209.623(4), and 2162.884(6) MHz; eQq(I)=687.01(2), 693.63(5), 725.96(4), and 727.8(1) MHz; ΔeQg(I)=-42(2), -50(6), -210(14), and -141(25) kHz; DJ=8.86(3), 8.25(6), 8.1(6), and 8.6(5) kHz. This complex has an interesting triangular structure with the H-I and H-F bonds making an acute angle of 70.1 (2.8)°. The iodine atom is coaxial with HF with a heavy atom separation R0(I-F)=3.660(8) Å. Hyperfine structure due to deuterium quadrupole coupling and H-F spin-spin interactions was resolved and measured.
• Bumgarner, R. E., Pauley, D. J., & Kukolich, S. G. (1987). Microwave spectra and structure for SO₂⋯H₂S, SO₂⋯HDS, and SO₂⋯D₂S complexes. The Journal of Chemical Physics, 87(7), 3749-3752.
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  Abstract: Microwave spectra for the SO2⋯H2S, SO 2⋯HDS, and SO2⋯D2S complexes were measured using a pulsed beam, Fourier transform microwave spectrometer. Both a-dipole and c-dipole transitions were obtained. A total of 24 transitions were obtained for SO2⋯H2S, yielding A = 8447.3(2), B = 1762.004(7), C= 1538.483(7) MHz, ΔJ = 5.04(2), ΔJK = 65.46(9), ΔK = -323(240), δJ = 0.63(1) and δK = 38(3) kHz. For SO 2⋯HDS, nine transitions yielded A = 8229.7(6), B = 1737.99(1), C= 1519.69(2) MHz, ΔJ = 4.4(4) and ΔJK = 60(2) kHz, and for SO2⋯D2S, 11 transitions yielded A = 8017.6(6), B = 1715.24(2), C = 1501.24(2) MHz, and ΔJ = 3.8(4), ΔJK = 51(2) kHz. For the H2S data only, there are four possible structures for the complex which fit the data. When the deuterium isotope data are included, only two possible structures fit the data. There is only one structure which allows two O⋯H hydrogen bonds, and this is the structure we favor. This analysis basically gives a "stacked" structure with two O⋯H hydrogen bonds and a near van der Waals radius contact between the two sulfur atoms. © 1987 American Institute of Physics.
• Choe, J. -., Kwak, D. K., & Kukolich, S. G. (1987). Fourier transform spectra of the 2100-cm^-1 bands of HCN. Journal of Molecular Spectroscopy, 121(1), 75-83.
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  Abstract: The 2100-cm-1 bands of various isotopes of HCN have been measured with a resolution of about 0.01 cm-1 using the Fourier transform spectrometer constructed by J. Brault and co-workers at the National Solar Observatory. The frequencies of 500 HCN lines obtained from absorption spectra of three different isotopic species are reported with an accuracy of approximately 0.0001 cm-1. Six bands of HCN, two bands of H13CN, and two bands of HC15N were measured. The 001 ← 000 and 0310 ← 000 of H13CN were reported for the first time. New measurements of 0330 ← 000 forbidden transitions (Δl = 3) were made. © 1987.
• KUKOLICH, S., & NELSON, A. (1987). HIGH RESOLUTION ROTATIONAL SPECTRA OF FORMAMIDE. CHEMICAL PHYSICS LETTERS, 11(3), 383-&.
• Kukolich, S. G., Bumgarner, R. E., & Pauley, D. J. (1987). The microwave spectrum of the ONN-HF complex. Chemical Physics Letters, 141(1-2), 12-15.
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  Abstract: Microwave transitions for the ONN-HF complex were measured using a pulsed-beam, Fourier transform spectrometer. This second structural isomer of the binary N2O-HF complex was detected earlier using IR spectroscopy. The rotational constant B = 1828.2835 (7) Mhz and distortion constant DJ= 2.97 (2) Khz were obtained. Only K= 0 transitions were observed. © 1987.
• WANG, J., OATES, D., , ., & KUKOLICH, S. (1987). MEASUREMENTS OF RELAXATION CROSS-SECTIONS FOR NH3 AND OCS WITH A MOLECULAR-BEAM MASER SPECTROMETER. JOURNAL OF CHEMICAL PHYSICS, 59(10), 5268-5276.
• Choe, J. -., Tipton, T., & Kukolich, S. G. (1986). Fourier transform spectra of the 3300 cm^-1 bands of HCN. Journal of Molecular Spectroscopy, 117(2), 292-307.
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  Abstract: The 3300-cm-1 bands of various isotopes of HCN have been measured with a resolution of about 0.01 cm-1 using the Fourier transform spectrometer constructed by J. Brault and co-workers at the National Solar Observatory. The frequencies of 910 HCN lines obtained from absorption spectra of three different isotopic species are reported with an accuracy of approximately 0.0001 cm-1. Six bands of HCN, four bands of H13CN, and two bands of HC15N were analyzed to obtain band origins, rotational constants, and l-doubling constants. The first (1110 ← 0110) and second (1200 ← 0200 and 1220 ← 0220) hot bands of H13CN are measured at high resolution for the first time. The fine structures of the Q branches of (110 ← 010), (1220 ← 0220), and (1330 ← 0330) "hot bands" of HCN have been completely resolved and measured. The accuracies of the calculated band origins are better than 0.0001 cm-1 for most bands, and the upper state rotational constants (B′) have accuracies which range from 1 × 10-7 to 5 × 10-6 cm-1 (0.003 to 0.015 MHz). © 1986.
• Pauley, D. J., Bumgarner, R. E., & Kukolich, S. G. (1986). Microwave spectrum of the SO₂-H₂S complex. Chemical Physics Letters, 132(1), 67-68.
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  Abstract: Ten ΔJ= 1 rotational transitions for the SO2-H2S complex were observed in the 4-12 GHz frequency range using a pulsed-beam Fourier-transform microwave spectrometer. The complex is a near-prolate asymmetric top with 1 2(B + C) = 1649(6) MHz and B - C = 228(10) MHz. Some of the observed transitions show inversion or hindered internal rotation splittings. A tentative structure is a non-planar cyclic complex containing two hydrogen bonds from H2S to the oxygen atoms on SO2. © 1986.
• Tipton, T., Choe, J. -., & Kukolich, S. G. (1986). Fourier transform infrared spectra of the 2v₂ and v₂ + v₄ bands of PH₃. Journal of Physical Chemistry, 90(8), 1534-1537.
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  Abstract: The lowest-lying overtone (2v2) and combination (v2 + v4) bands of phosphine have been investigated for the first time with a Fourier transform spectrometer with 0.01-cm-1 resolution. A least-squares fit which includes Coriolis coupling parameters has been performed on both bands simultaneously. The resulting constants fit 400 transitions with a standard deviation of 0.05 cm-1. Rotational parameters for the excited states and vibrational frequencies are obtained from the analysis. © 1986 American Chemical Society.
• Bumgarner, R. E., Cogley, C. D., & Kukolich, S. G. (1985). Microwave spectrum of the HI-HF complex. Chemical Physics Letters, 122(6), 535-537.
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  Abstract: Twenty-seven ΔJ = +1 rotational transitions for the HI-HF complex were observed in the 8-18 GHz frequency range. The lines were measured 10 an accuracy of 5 kHz using a pulsed-beam Fourier transform microwave spectrometer. The spectroscopic constants obtained by fitting the observed transitions are 21(B + C) = 2220.74746(82) MHz DJ = 8.842(32) kHz eqQ = 687.012(26) MHz and Δ(eqQ) = -40.6(2.6) kHz. © 1985.
• KUKOLICH, S., ROEHRIG, M., WALLACE, D., & HENDERSON, G. (1985). MICROWAVE MEASUREMENTS OF THE ROTATIONAL SPECTRUM AND STRUCTURE OF (BUTADIENE)IRON TRICARBONYL. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 115(5), 2021-2027.
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  The rotational spectra of 10 isotopomers of (butadiene)iron tricarbonyl were measured using a Flygare-Balle-type microwave spectrometer operating in the 5-17-GHz frequency range. The 30 measured rotational constants were used to determine 12 gas-phase structural parameters describing the cis-butadiene conformation and the locations and orientations of the butadiene and CO ligands relative to the iron atom. Kraitchman analyses of these microwave measurements, with single and multiple deuterium substitution, provide accurate data on the hydrogen atom coordinates in the complex. The terminal CH2 groups of butadiene are found to be rotated by 28-degrees out of the butadiene plane, and the CH2 plane is folded away from the C1-C2 axis by 27-degrees in a direction away from the iron atom. Least-squares fits to all rotational constants to determine structural parameters were also carried out, and the results are compared with coordinates from the Kraitchman method. Other structural parameters are compared with X-ray diffraction results on similar compounds. The four possible single-substitution C-13 isotopomers were observed in natural abundance samples. Samples for the two D1, two D3, and D4 substitutions on terminal H atoms were synthesized. Proton NMR spectra were analyzed to obtain improved chemical shifts and coupling constants for this complex.
• Tipton, T., Choe, J. -., Kukolich, S. G., & Hubbard, R. (1985). Fourier transform spectroscopy on the 3ν₂, 2ν₂ + ν₆ and ν₃ + ν₅ bands of H₂CO. Journal of Molecular Spectroscopy, 114(2), 239-256.
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  Abstract: Fourier transform spectra covering the range from 1500 to 5400 cm-1 with 0.02-cm-1 resolution have been obtained for formaldehyde. A study of the region above 4000 cm-1 has yielded rotational constants and other asymmetric rotor parameters for three bands: 3ν2 (ν0 = 5177.7611 ± 0.0005 cm-1)2ν2 + ν6 (ν0 = 4734.193 ± 0.004 cm-1), and ν3 + ν5 (ν0 = 4335.102 ± 0.001 cm-1). An analysis of the A-type Coriolis interaction between the 2ν2 + ν6 state and the unobserved 2ν2 + ν4 state has yielded partially deperturbed rotational constants for the 2ν2 + ν6 state. Vibration-rotation interaction constants have been obtained for the ν2 and ν6 normal modes by combining the present results with those of previous workers. © 1985.
• Young, S., & Kukolich, S. (1985). Microwave measurements and calculations of quadrupole coupling effects in CH₃I and CD₃I. Journal of Molecular Spectroscopy, 114(2), 483-493.
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  Abstract: The transitions J = 1 ← 0, K = 0; J = 2 ← 1, K = 0; and J = 2 ← 1, K = 1 of CH3I and CD3I were measured using a Stark-modulated microwave spectrometer. Iodine quadrupole coupling strengths were analyzed to determine variations with deuterium substitution on the methyl group and variations with centrifugal distortion. Quadrupole coupling strengths were described by the expression eQq0 + aJ(J + 1) + bK2 + cK4 J(J + 1). Explicit expressions are given for a, b, and c for a symmetric top in terms of molecular parameters. For CH3I eQq0 = -1934.11 ± 0.02 MHz and for CD3I eQq0 = -1928.95 ± 0.04 MHz. Rotational constants obtained are B(CH3I) = 7501.274 ± 0.002 MHz and B(CD3I) = 6040.298 ± 0.007 MHz. The observed fractional change in halogen quadrupole coupling of 0.0027 is related to previous results for methyl chloride and methyl bromide. © 1985.
• Aldrich, P. D., Kukolich, S. G., & Campbell, E. J. (1983). The structure and molecular properties of the acetylene-HCN complex as determined from the rotational spectra. The Journal of Chemical Physics, 78(6), 3521-3530.
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  Abstract: The microwave spectra for four isotopic species of a complex formed between acetylene and HCN have been obtained using the pulsed, Fourier-transform method with gas pulsed into an evacuated Fabry-Perot cavity. The spectra indicate the complex to be a T-shaped near-prolate asymmetric rotor (κ=-0.993) in its ground vibrational state in which HCN lies on the C2 symmetry axis with the hydrogen atom of HCN pointing to the middle of the triple bond of acetylene. The carbon atom of HCN is situated 3.656 Å from the acetylene center of mass. Nuclear quadrupole coupling constants for N are obtained for all four isotopes and deuterium quadrupole coupling constants are obtained for two isotopes. Various contributions to the electric field gradients at quadrupolar nuclei are discussed. © 1983 American Institute of Physics.
• Aldrich, P. D., Kukolich, S. G., Campbell, E. J., & Read, W. G. (1983). MAGNETIC SUSCEPTIBILITY ANISOTROPY, MOLECULAR g VALUES, AND OTHER MOLECULAR PROPERTIES OF CYCLOPROPANE AS DETERMINED FROM ROTATIONAL ZEEMAN STUDIES OF THE CYCLOPROPANE-H**3**5Cl AND CYCLOPROPANE-HC**1**5N COMPLEXES.. Journal of the American Chemical Society, 105(17), 5569-5576.
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  Abstract: A pulsed, Fourier-transform microwave spectrometer has been used to observe the rotational Zeeman effect with the cyclopropane-HCl and cyclopropane-HCN complexes. The molecular g values and magnetic susceptibility anisotropies have been determined for the cyclopropane-HCl complex and have been used to obtain the molecular quadrupole moment, magnetic susceptibility tensor elements as well as the paramagnetic and diamagnetic contributions, and the second moment of the electronic charge distribution. Certain Zeeman parameters along with zero-field rotational constants have been obtained for cyclopropane-HC**1**5N. The Zeeman constants for both complexes have then been used to extract various magnetic properties of cyclopropane.
• CAMPBELL, E., & KUKOLICH, S. (1983). ELECTRIC-DIPOLE MOMENTS OF (HCN-N-15)2 AND HCNHCL-N-15-CL-35. CHEMICAL PHYSICS, 76(2), 225-229.
• CASLETON, K., & KUKOLICH, S. (1983). MEASUREMENT OF DEUTERIUM QUADRUPOLE COUPLING IN CH3OD. CHEMICAL PHYSICS LETTERS, 22(2), 331-334.
• CHOE, J., TIPTON, T., & KUKOLICH, S. (1983). FOURIER-TRANSFORM SPECTRA OF THE 3300 CM-1 BANDS OF HCN. JOURNAL OF MOLECULAR SPECTROSCOPY, 117(2), 292-307.
• Campbell, E. J., & Kukolich, S. G. (1983). Electric dipole moments of (HC¹⁵N)₂ and HC¹⁵NH³⁵Cl. Chemical Physics, 76(2), 225-229.
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  Abstract: The electric dipole moments of two linear hydrogen-bound complexes containing HCN have been measured using pulsed Fourier-transform microwave spectroscopy carried out in a Fabry-Perot cavity. The dipole moment of (HC15N)2 is 6.552(35) D and the dipole moment of HC15NH35Cl is 4.817(24) D. Both measurements refer to the vibrational ground state. © 1983.
• Cogley, C. D., & Kukolich, S. G. (1983). Measurements of BrCN hyperfine structure. Journal of Molecular Spectroscopy, 97(1), 220-223.
• GAINES, L., CASLETON, K., & KUKOLICH, S. (1983). BEAM MASER MEASUREMENTS OF CH3OH ROTATIONAL TRANSITIONS. ASTROPHYSICAL JOURNAL, 191(2), L99-L100.
• HACKEL, L., CASLETON, K., KUKOLICH, S., & EZEKIEL, S. (1983). OBSERVATION OF MAGNETIC OCTUPOLE AND SCALAR SPIN-SPIN INTERACTIONS IN I2 USING LASER SPECTROSCOPY. PHYSICAL REVIEW LETTERS, 35(9), 568-571.
• KUKOLICH, S. (1983). MICROWAVE STRUCTURE MEASUREMENTS ON THE FURAN-ARGON COMPLEX. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 105(8), 2207-2210.
• KUKOLICH, S., & NELSON, A. (1983). CHLORINE QUADRUPOLE COUPLING IN METHYL CHLORIDE - VARIATION OF QUADRUPOLE COUPLING STRENGTH WITH ISOTOPIC SUBSTITUTION. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 95(3), 680-682.
• KUKOLICH, S., READ, W., & ALDRICH, P. (1983). MICROWAVE-SPECTRUM, STRUCTURE, AND QUADRUPOLE COUPLING FOR THE ETHYLENE HYDROGEN-CYANIDE COMPLEX. JOURNAL OF CHEMICAL PHYSICS, 78(6), 3552-3556.
• KUKOLICH, S., RUBEN, D., WANG, J., & WILLIAMS, . (1983). HIGH-RESOLUTION MEASUREMENTS OF N-14, D QUADRUPOLE COUPLING IN CH3CN AND CD3CN. JOURNAL OF CHEMICAL PHYSICS, 58(8), 3155-3159.
• Kukolich, S. G. (1983). Microwave structure measurements on the cyclopropane-HCN complex. The Journal of Chemical Physics, 78(8), 4832-4835.
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  Abstract: Microwave rotational transitions for the cyclopropane-HCN complex were observed using the Flygare-Balle pulsed beam Fourier transform spectrometer. The 111→212, 101→202, 1 10→211, 212→313, 2 02→303, 211→312, 3 13→414, 303→404, 3 12→413, 414→515, 4 04→505, and 413→514 transitions were observed. The rotational constants obtained are A=20 243±1344 MHz, B=1384.209±0.001 MHz, and C=1327.901±0.001 MHz. The distortion constants are DJ=1.53±0.03 kHz and D JK=50.9±p1.1 kHz. The nitrogen quadrupole coupling strength is eQqaa=-4.38±0.01 MHz with eQqbb-eQq cc=0.002±0.003 MHz. The cyclopropane carbon atoms and HCN lie in a plane. The most reasonable bond distance is obtained with the HCN hydrogen atom bonding to the midpoint between two of the cyclopropane carbon atoms. The separation of the centers of mass of HCN and cyclopropane is R cm=4.472±0.002 Å. The HCN carbon atom is R CC-C=3.476±0.002 Å from the cyclopropane carbon-carbon bond. The stretching force constant is ks=0.062 mdyn/Å and the approximate bonding energy is 860 cm-1. © 1983 American Institute of Physics.
• Kukolich, S. G. (1983). Microwave structure measurements on the furan-argon complex. Journal of the American Chemical Society, 105(8), 2207-2210.
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  Abstract: Rotational transitions were measured for furan-argon and [2-D]furan-argon using a pulsed nozzle Fourier transform spectrometer. Analysis of the data indicates that the argon atom is above the plane of furan, a distance of 3.54 Å from the furan center of mass. The line between the argon and furan center of mass makes an angle of 11° with the furan c axis with the displacement toward the oxygen atom of furan. Measured rotational constants for argon-furan are A = 4802.340 (3), B = 1362.612 (2), and C = 1360.289 (2) MHz. For argon-[2-D]furan, A = 4591.442 (18), B = 1358.191 (4), and C = 1338.736 (2) MHz. An analysis of the centrifugal distortion and interaction potential is given for this complex. The stretching force constant is ks = 0.27 mdyn/Å and the approximate well depth is ∈ = 236 cm-1. © 1983 American Chemical Society.
• Kukolich, S. G. (1983). Structure and quadrupole coupling measurements on the NO dimer. Journal of Molecular Spectroscopy, 98(1), 80-86.
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  Abstract: Rotational transition frequencies for 14NO-14NO, 14NO-15NO, and 15NO-15NO were measured using a pulsed-nozzle Fourier transform microwave spectrometer. Rotational constants for the different isotopic combinations allowed an unambiguous structure determination. The molecule is in a cis planar structure with a bond between the nitrogen atoms and an NNO angle θ = 99.6(2)°. The NN bond length is 2.236(1) Å and the NO bond length is 1.161(4) Å. Hyperfine structure due to nitrogen quadrupole coupling and spin-rotation interactions was observed and analyzed. Rotation constants, quadrupole coupling tensor, and spin-rotation tensor elements are given. © 1983.
• Kukolich, S. G., & Campbell, E. J. (1983). Microwave measurements of bromine quadrupole coupling constants and the molecular structure of XeHBr. Chemical Physics Letters, 94(1), 73-76.
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  Abstract: Microwave rotational spectra for various isotopic forms of the XeHBr complex were obtained using a pulsed-nozzle, Fourier transform spectrometer. The molecular constants (eQq), B0 and Dj were obtained from J = 6 → 7, 7 → 8 and 8 → 9 transitions. The xenon-bromine separation distance is rXe-Br = 4.419 Å. From Dj a stretching force constant ks = 0.018 mdyne/Å and well depth ε{lunate} = 244 cm-1 were obtained. © 1983.
• Kukolich, S. G., Aldrich, P. D., Read, W. G., & Campbell, E. J. (1983). Molecular Zeeman effect measurements on the ethylene-HCl complex. The Journal of Chemical Physics, 79(3), 1105-1110.
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  Abstract: The molecular g values and magnetic susceptibility anisotropies for the ethylene-HCl complex were measured using pulsed Fourier transform microwave spectroscopy in magnetic fields of 25 and 30 kG. Values obtained are g aa=0.0383(5), gbb=-0.0072(3), gcc=-0.0082(2), 2χaa-χbb-χcc=-4.27(0.06), and 2χbb-χaa-χcc=1.05 (0.08)×10-9 MHz/G2. Quadrupole moments for the complex are Qaa=-2.30(24)×10-26 esu cm2, Qbb=2.40(38)×10-26 esu cm2, and Q cc=-0.10(35)×10-26 esu cm2. From this data molecular quadrupole moments and other Zeeman parameters are derived for ethylene. © 1983 American Institute of Physics.
• Kukolich, S. G., Read, W. G., & Aldrich, P. D. (1983). Microwave spectrum, structure, and quadrupole coupling for the ethylene-hydrogen cyanide complex. The Journal of Chemical Physics, 78(6), 3552-3556.
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  Abstract: Microwave spectra for the complexes ethylene-HCN and ethylene-DCN were observed with the pulsed beam, Fourier transform spectrometer. The complexes are "T" shaped with the HCN hydrogen atom adjacent to the C-C double bond of ethylene. The HCN molecule lies on a line perpendicular to the plane of ethylene and passing through the ethylene center of mass. The HCN carbon atom is 3.702(10) Å above the ethylene plane. The nitrogen quadrupole coupling strength is eQqaa(N)=-4.363(2)MHz for ethylene-HCN and Qq aa(N)=-4.396(3) MHz for ethylene-DCN. The deuterium quadrupole coupling strength is eQqaa (D)=0.178(7) MHz for ethylene-DCN. The anisotropy in the nitrogen quadrupole coupling eQ(qbb -qdd)(N) is 0.013(3) MHz for ethylene-HCN and 0.047(12) MHz for ethylene-DCN. The rotational constants are ABC ethylene-HCN 25496(689) 1906.581(5) 1808.878(5) ethylene-DCN 24960(1101)1904.739(6) 1807.344(6) entrifugal distortion constants D1 and D3K were obtained. © 1983 American Institute of Physics.
• Kukolich, S. G., Read, W. G., Shea, J. A., & Campbell, E. J. (1983). MEASUREMENTS OF MOLECULAR g VALUES, MAGNETIC SUSCEPTIBILITY ANISOTROPIES, AND QUADRUPOLE MOMENTS FOR THE ACETYLENE-HCl COMPLEX.. Journal of the American Chemical Society, 105(21), 6423-6426.
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  Abstract: Rotational transitions for acetylene-HCl were measured in magnetic fields of 28 and 30 kG using a pulsed-nozzle, Fourier transform microwave spectrometer. Measured molecular g values are g//a//a equals 0. 0519 (5), g//b//b equals minus 0. 0006 (2), and g//c//c equals 0. 0025 (2). Susceptibility anisotropies are 2// CHI //a//a minus // CHI //b//b minus // CHI //c//c equals 0. 08 (4) multiplied by 10** minus **9 and 2// CHI //b//b minus // CHI //c//c minus // CHI //a//a equals minus 1. 14 (8) multiplied by 10** minus **9 MHz/G**2. Molecular quadrupole moments for the complex are Q//a//a equals minus 2. 6 (3), Q//b//b equals 6. 2 (3), and Q//c//c equals minus 3. 7 (3) multiplied by 10** minus **2**6 esu cm**2. The authors find that the molecular g value for acetylene is positive. The molecular quadrupole moment of acetylene is found to be 8. 0 (16) multiplied by 10** minus **2**6 esu cm**2 in good agreement with calculated values.
• Murray, A. M., & Kukolich, S. G. (1983). Beam maser spectroscopy on CD₃CN. The Journal of Chemical Physics, 78(6), 3557-3559.
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  Abstract: The J=1→0 rotational transitions of CD3CN were measured using a two-cavity molecular beam maser spectrometer. This spectrometer employs the Ramsey method of separated oscillating fields to obtain very high resolutions and allows precise measurements of the hyperfine structure splittings. The nitrogen quadrupole coupling constant is eqaa(N)=- 4229.2±0.6 kHz and the deuterium quadrupole constant is eq aaQ(D)=-55.1±0.4 kHz. Assuming cylinderical symmetry about the C-D bond axis we obtain the C-D bond-axis deuterium quadrupole coupling strength of eqzzQ(O)=169.6±4.5 kHz. The A-axis rotational constant, and nitrogen and deuterium spin-rotation interaction strengths are also reported. © 1983 American Institute of Physics.
• Shea, J. A., & Kukolich, S. G. (1983). The rotational spectrum and molecular structure of the furan-HCI complex. The Journal of Chemical Physics, 78(6), 3545-3551.
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  Abstract: The microwave spectrum of the furan-HCl complex in the ground vibrational state has been measured and assigned using a Fourier-transform microwave spectrometer employing a Fabry-Perot cavity and a pulsed supersonic nozzle as a molecular source. Furan-HCl is planar, with the axis of the HCl subunit oriented along the a axis of furan, bisecting the oxygen-carbon angle. A hydrogen bond is formed between the HCl proton and the lone electron pair of oxygen. The spectroscopic constants for furan-H35Cl in MHz are A″=9421.3(39), B″=1004.2001(27), C″=904.5526(26), τT 1=-0.9392(12), τ2=-0.0751(2), τbbbb=-0. 004 01(19), τcccc=-0.002 17(17), χaa=-52.803(17), χbb=25.626(54), and χcc=27.177(54). Rotational transitions for the isotopic species furan-H 37Cl and furan-D 35Cl were also measured and assigned. The oxygen-chlorine distance is 3.26(1) Å. The binding of the HCl to oxygen, rather than to the π bonds between the âcarbon atoms, was confirmed by measurements on the 2-D furan-H 35Cl complex. © 1983 American Institute of Physics.
• TACK, L., & KUKOLICH, S. (1983). BEAM MASER MEASUREMENTS OF HYPERFINE-STRUCTURE IN CHLOROACETYLENE-D. JOURNAL OF MOLECULAR SPECTROSCOPY, 94(1), 95-99.
• Tack, L. M., & Kukolich, S. G. (1983). Beam-maser spectroscopy on cyanoacetylene-D. The Journal of Chemical Physics, 78(11), 6512-6514.
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  Abstract: The J=1→0 transition frequencies were measured for NCCCD using a beam-maser spectrometer. Hyperfine structure from 14N and D was completely resolved. Analysis of the data directly gives the 14N and deuterium quadrupole coupling constant along the internuclear axis eqQ( 14N)=-4318.0±0.1 kHz, eqQ(D)=203.5±1.5 kHz. From the data the spin-rotation constant on 14N was also measured: C( 14N)=1.1±0.2 kHz. The spin-rotation data were used to calculate paramagnetic chemical shift tensor components σ xxp=σyyp=-593±40 ppm. These experimentally determined tensor components were combined with calculated diamagnetic tensor components to give the isotropic shift σav= 18±27 ppm. © 1983 American Institute of Physics.
• ALDRICH, P., KUKOLICH, S., & CAMPBELL, E. (1982). THE STRUCTURE AND MOLECULAR-PROPERTIES OF THE ACETYLENE-HCN COMPLEX AS DETERMINED FROM THE ROTATIONAL SPECTRA. JOURNAL OF CHEMICAL PHYSICS, 78(6), 3521-3530.
• Fry, H. A., & Kukolich, S. G. (1982). Beam maser measurements of HDO hyperfine structure. The Journal of Chemical Physics, 76(9), 4387-4391.
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  Abstract: The 431←432, 532←533, and 321←414 transition in HDO were measured in a beam maser spectrometer. Accurate values for rotational transiton frequencies, the deuterium quadrupole coupling tensor, and hydrogen spin-rotation tensor were obtained from the present data combined with previous results on other transitions. Resonance line widths of 2 kHz were obtained for most of the data. Measured quadrupole coupling tensor elements eqQ(D)gg and spin-rotation tensor elements C(X)gg in kHz are as follows: eqQ(D)aa=276.45±0.88, eqQ(D)bb=-110.97±1.46, eqQ(D)cc=-165.77±1.10, C(D)aa=-1.33±0.20, C(D)bb=-4.38±0.36, C(D)cc=-2.99±0.24, C(H)aa=-58.42±0.47, C(H)bb=-5.46±0.83, C(H)cc=-24.11±0.55. © 1982 American Institute of Physics.
• KUKOLICH, S., SICKAFOOSE, S., FLORES, L., & BRECKENRIDGE, S. (1982). MEASUREMENTS OF THE MICROWAVE-SPECTRUM AND STRUCTURAL PARAMETERS FOR BENZENE CHROMIUM TRICARBONYL. JOURNAL OF CHEMICAL PHYSICS, 100(9), 6125-6128.
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  Microwave spectra for four isotopomers of benzene chromium tricarbonyl were measured in the 4-17 GHz range using a Flygare-Balle type pulsed beam spectrometer. Rotational constants obtained are B(Cr-52)=732.8886(6) MHz and B(Cr-53)=732.8966(3) MHz. Asymmetric top spectra were observed for a single C-13 substitution on the benzene ring giving B(C-13-bz)=729.9606(3) and C(C-13-bz)=727.9024(2) MHz. For a single C-13 substitution on one of the carbonyl carbons B((CO)-C-13)=731.9036(8) and C((CO)-C-13)=729.1657(8) MHz. Since no effects of possible internal rotation were observed on the C-13 asymmetric top spectra, we can place a lower limit on the V-6 potential for internal rotation of V-6>4.0 THz (=1.6 kJ/mole). The centrifugal distortion constants are small, D-J=0.05 kHz and D-JK=-0.05 kHz, indicating a fairly rigid structure. The Cr-53 quadrupole coupling strength is low, eqQ(Cr-53)=-12.11(1) MHz, indicating a near octahedral charge distribution around the Cr atom. Structural parameters obtained are the center of the benzene chromium distance r(Cr-bz)=1.67(2) Angstrom, the chromium-carbonyl bond length r(Cr-CO)=1.86(1) Angstrom and the OC-Cr-CO interbond angle alpha=88(1)degrees.
• Kukolich, S. G. (1982). Beam maser spectroscopy on J=1→2, K=1, and K=0 transitions in CH ₃CN and CH₃¹³CN. The Journal of Chemical Physics, 76(1), 97-101.
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  Abstract: J=1→2 transitions near 36.8 GHz in CH3CN and CH313CN were measured using a beam maser spectrometer. K=1 transitions were observed with a 10 kHz linewidth (FWHM) and K=0 transitions were observable with a two-cavity Ramsey system with about 3 kHz resolution. The measured difference between a axis and c axis nitrogen spin-rotation tensor components is Ca-Cc=4.6±1.0 kHz for CH3CN and 4.5±1.0 kHz for CH313CN. The c axis nitrogen spin-rotation tensor component is Cc=2.0±0.4 kHz. Nitrogen chemical shift tensor components of σa=247 ppm and σc=-165 ppm are obtained from the data and calculated diamagnetic contributions. The measured paramagnetic contributions to the nitrogen chemical shift tensor are σap=-98±15 ppm and σcp=-600±120 ppm. Nitrogen quadrupole coupling strength is eqQ=-4224.3±4.0 kHz and rotational transition frequencies are: 36 795 476.9±3.0 kHz (CH3CN, K=0), 36 794 769.3±1.5 kHz (CH3CN, K=1), 36 777 282.6±3.4 kHz (CH313CN, K=0), and 36 776 573.3±1.6 kHz (CH313CN, K=1). This data, combined with previous J=0→1 data yields accurate rotation and distortion constants for CH 3CN and CH313CN as follows: CH3CN CH313CN B 9 198 899.3±1.0 9 194 347.1±0.7 KHz DJ 3.7±0.3 3.3±0.3 KHz DJK 176.9±1.0 177.3±0.7 KHz. © 1982 American Institute of Physics.
• Kukolich, S. G. (1982). Nitrogen quadrupole coupling measurements on ON-NO₂ using the Flygare-Balle pulsed-beam spectrometer. Journal of the American Chemical Society, 104(25), 6927-6929.
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  Abstract: High-resolution measurements of the I01 ← 000, 212 ← 111, 202 ← 101, 211 ← 10, 312 ← 313, and 413 ← 414 transitions in the ON-NO2 complex were made by using a pulsed-beam, Fourier transform microwave spectrometer. Nearly all hyperfine structure components were resolved on observed transitions except for the 202 ← 101 group. The quadrupole coupling tensors in the principal axis system were determined for both nitrogen atoms. The nitrogen quadrupole coupling components for the NO group are eQqaa = -1.7766 ± 0.0037 MHz and eQqbb = 0.0585 ± 0.0021 MHz. For the NO2 group eQqaa = -0.5260 ± 0.0035 MHz and eQqbb = -4.1941 ± 0.0018 MHz. The rotational constants obtained are A = 12412 ± 22 MHz, B = 4226.530 ± 0.012 MHz, and C = 3152.966 ± 0.012 MHz. Rotational transition frequencies and estimates of spin-rotation interaction strengths are given. The observed quadrupole coupling strengths are substantially different from those observed for the free NO and NO2 molecules. © 1982 American Chemical Society.
• Kukolich, S. G. (1982). Structure of the NO dimer. Journal of the American Chemical Society, 104(17), 4715-4716.
• Kukolich, S. G., & Cogley, C. D. (1982). Deuterium hyperfine structure measurements and theory for CD₃Br. The Journal of Chemical Physics, 76(4), 1685-1691.
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  Abstract: Hyperfine structure on the J=1→0, F1 = 3/2 transitions in CH379Br, CH381Br, and CD 379Br was measured with one-cavity and two-cavity beam maser spectrometers. The resolution for the measurements was approximately 2 kHz and most hyperfine structure components were completely resolved. Deuterium quadrupole coupling eQq12=178.5±3 kHz along the C-D bond and other parameters were obtained. In the theory section, formulas for the hyperfine interaction strengths with three equivalent spins are presented and reviewed. Deuterium quadrupole coupling in other C-D bond systems is discussed. © 1982 American Institute of Physics.
• Kukolich, S. G., & Cogley, C. D. (1982). Erratum: Deuterium hyperfine structure measurements and theory for CD ₃Br (The Journal of Chemical Physics (1982) 76 (1685)). The Journal of Chemical Physics, 77(1), 581-.
• Kukolich, S. G., & Shea, J. A. (1982). The microwave spectrum and molecular structure of the furan-argon complex. The Journal of Chemical Physics, 77(10), 5242-5243.
• Kukolich, S. G., Aldrich, P. D., Read, W. G., & Cambell, E. J. (1982). Microwave structure determination and quadrupole coupling measurements on acetylene-HCN and ethylene-HCN complexes. Chemical Physics Letters, 90(5), 329-331.
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  Abstract: Microwave rotational spectra for the complexes HCCH-HCN, HCCH-DCN, DCCD-HCN, H2CCh2-HCN and H2CCH2-DCN were observed using a pulsed nozzle Fourier transform spectrometer. The distance from the HCN carbon atom the the center of mass is. 3.655(10) Å for acetylene-HCN and 3.709(10) Å for ethylene-HCN. Both complex are T-shaped with the HCN hydrogen atom closest to the CC bond. The HCN axis is perpendicular to the plane of ethylene for ethylene-HCN. Nitrogen and deuterium quadrupole coupling was measured. © 1982.
• Kukolich, S., Schaum, L., & Murray, A. (1982). Measurements of rotational transitions and hyperfine structure in PH₂D. Journal of Molecular Spectroscopy, 94(2), 393-398.
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  Abstract: New rotational transition frequencies and measurements of hyperfine structure on two transitions are reported for PH2D. All observed transitions are Q branch (ΔJ = 0) so only two independent rotational constants are obtained. These are A-C = 46 593.44 ± 0.67 MHz and κ(A-C) = 2B-A-C = -34 545.9 ± 1.3 MHz. Nine transitions were fit to these parameters and the distortion parameter DJK to obtain DJK = 4.30 ± 0.04 MHz. Hyperfine structure due to spin-rotation interactions was observed on the 110 ← 111 transition at 6 024.645 MHz and on the 414 ← 404 transition at 20 815.334 MHz. Spin-rotation tensor components obtained are (Maa + Mbb) 2 = (Maa + Mcc) 2 = -98 ± 3 kHz. © 1982.
• Kukolich, S., Sickafoose, S., & Breckenridge, S. (1982). Microwave molecular structure measurements for tetracarbonyldihydroosmium, a classical dihydride. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 118(1), 205-208.
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  Microwave rotational spectra for six isotopomers of H2Os(Co)(4) were measured in the 4-12 GHz range using a Flygare-Balle-type spectrometer. The 18 rotational constants from these isotopomers were used to determine eight structural parameters describing the gas-phase structure of this complex. This near-octahedral complex has C-2v symmetry and the dipole moment lies along the c-principal axis for the normal isotopomer. The distance between H atoms, obtained directly from experimental structural parameters, is r(HH) = 2.40(2) Angstrom. This rather long H-H distance indicates that this is clearly a ''dihydride'' rather than a ''dihydrogen'' complex. The Os-H bond lengths are r(OsH) = 1.72(1) Angstrom. The osmium-carbonyl carbon bond lengths for axial and equatorial carbonyl groups are ro,cl = 1.96(1) Angstrom and r(OsC3) = 1.97(2) Angstrom. Results for other structural parameters obtained using least-squares fitting and the structural parameters obtained using the Kraitchman method are presented and discussed. No evidence for internal motion was observed for this complex.
• LEVY, J., , ., WANG, J., & KUKOLICH, S. (1982). TRANSIENT-NUTATION EFFECTS IN TIME-RESOLVED INFRARED-MICROWAVE DOUBLE-RESONANCE OF AMMONIA. PHYSICAL REVIEW LETTERS, 29(7), 395-&.
• Murray, A. M., & Kukolich, S. G. (1982). Deuterium quadrupole coupling in BD₃CO. The Journal of Chemical Physics, 77(9), 4312-4317.
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  Abstract: The hyperfine structure of the J = 1→0 rotational transitions of 10BH3CO, 11BH3CO, and 11BD3CO was observed with a molecular beam maser spectrometer. Rotational constants, quadrupole coupling, spin rotation, and spin-spin interaction constants were determined from the data analysis. The deuterium quadrupole coupling constant in 11BD3CO, was determined to be eQqaa(D) = -48.5±2.3 kHz and eQq zz(D) = 116.9±5.4 kHz. The procedure for determining the matrix elements of the spin-spin interaction between the equivalent deuterium nuclei is presented. © 1982 American Institute of Physics.
• Shea, J. A., & Kukolich, S. G. (1982). Microwave structure determination for the furan-HCl complex. Journal of the American Chemical Society, 104(18), 4999-5000.
• TIPTON, T., CHOE, J., KUKOLICH, S., & HUBBARD, R. (1982). FOURIER-TRANSFORM SPECTROSCOPY ON THE 3V2, 2V2+V6 AND V3+V5 BANDS OF H2CO. JOURNAL OF MOLECULAR SPECTROSCOPY, 114(2), 239-256.
• Tack, L. M., & Kukolich, S. G. (1982). Beam maser measurements of hyperfine structure in chloroacetylene-d. Journal of Molecular Spectroscopy, 94(1), 95-99.
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  Abstract: The J = 1-0 transitions in 35ClCCD were measured using a beam maser spectrometer giving a molecular resonance linewidth of 3 kHz (FWHM). Analysis of the data yielded quadrupole coupling strengths eqQ(D) = 208.5 ± 1.5, eqQ(35Cl)= 79 739.5 ± 1 kHz and the 35Cl spinrotation interaction strength C(Cl) 1.3 ± 0.1 kHz. The rotational constant obtained is B = 5 186 973.9 ± 1.0 kHz. The accuracy of measured molecular parameters is improved by a factor of 20 or better. © 1982.
• Tackett, B. S., Karunatilaka, C., Daly, A. M., & Kukolich, S. G. (1982). Microwave spectra and gas-phase structural parameters of bis(eta(5)-cyclopentadienyl)tungsten dihydride. ORGANOMETALLICS, 26(8), 2070-2076.
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  Microwave spectra for 11 isotopomers of bis(eta(5)-cyclopentadienyl)tungsten dihydride ((C5H5)(2)WH2) were recorded in the 5-14 GHz region using a Flygare-Balle-type pulsed beam spectrometer. Spectra arising from four tungsten isotopomers of both the (C5H5)(2)WH2 and (C5H5)(2)WHD species and three W isotopomers for the (C5H5)(2)WD2 complex have been measured. The similar to 250 b-type transition frequencies assigned for these near-prolate asymmetric top molecules were accurately described (sigma(fit) = 2-4 kHz) using the rotational parameters A, B, and C and one centrifugal distortion constant, Delta(J). The small value obtained for Delta(J) indicates a fairly rigid structure. From a least-squares fit using the resulting 33 rotational constants to obtain the molecular structure, we were able to determine the W-H bond length, r(W-H) = 1.703(2) A, the H-W-H bond angle, >(H-W-H) = 78.0(12)degrees, the W-Cp centroid distance, r(W-Cp) = 1.940(8) A, the angle made by the Cp centroids with tungsten, >(Cp-W-Cp) = 155(2)degrees, and the average C-C bond length, r(C-C) = 1.429(8) A. The hydrogen atom separation is r(H-H) = 2.14(2) A, indicating that this is clearly a "classical dihydride" rather than an "eta(2)-dihydrogen" complex. The WH2 moiety parameters determined from Kraitchman's equations (r(W-H) = 1.682(2) A, >(H-W-H) = 78.6(2), r(H-H) = 2.130(2) A) agree well with the least-squares results. Furthermore, the r(e) parameters obtained from DFT calculations agree well with the experimental r(0) structural parameters. To our knowledge, this work marks the first microwave study of a bent-metallocene complex. The present measurements were made with a pulsed-beam Fourier transform spectrometer employing a homodyne-type detection system, and this configuration is described. This homodyne system greatly simplifies the microwave circuit, with no apparent loss in sensitivity.
• Cogley, C. D., Tack, L. M., & Kukolich, S. G. (1981). Beam maser spectroscopy on CH₃CCD and CD₃CCH. The Journal of Chemical Physics, 76(12), 5669-5671.
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  Abstract: The J=1→0 transition frequencies in CH3CCD and CD 3CCH were measured using a beam maser spectrometer. Hyperfine structure from deuterium quadrupole coupling was well resolved. The measured deuterium quadrupole coupling tensor components along the symmetry axis are eQqaa=228±2 kHz for CH3CCD and eQq aa=-55.0±0.5 kHz for CD3CCH. The coupling strength along the bond direction for CD3CCH is eQqzz=174±6 kHz. These results are compared with the other deuterium quadrupole coupling values. Measured rotational constants are B=7 778 170±1 kHz for CH 3CCD and B=7 355 767±1 kHz for CD3CCH. © 1982 American Institute of Physics.
• Cogley, C. D., & Kukolich, S. G. (1980). TRAVELLING WAVE TUBE MICROWAVE SPECTROMETER.. Journal of Physics E: Scientific Instruments, 13(7), 761-762.
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  Abstract: The sensitivity of a Stark-modulated waveguide microwave spectrometer can be significantly improved by using a traveling wave tube or solid state microwave amplifier prior to the crystal detection. In this paper the traveling wave tube is discussed. The increase in sensitivity results from the improved noise figure of the traveling wave tube relative to crystal video type detectors. Wide bandwidth traveling wave tube or solid state amplifiers are available so full waveguide bandwidths may be utilized. Rotational transitions for J equals 1 yields 0 lines of cyanogen bromide, BrCN, were measured with the traveling wave tube system and a standard video detector and the spectra are given here.
• Cogley, C., Fry, H., & Kukolich, S. (1979). Measurement of Cl and N quadrupole coupling in ClCN. Journal of Molecular Spectroscopy, 75(3), 447-453.
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  Abstract: J = 1 ← 0 and J = 2 ← 1 transitions in 35ClCN and 37ClCN were measured using a C-band waveguide spectrometer and phase-locked sources. Parameters obtained from the data are: B(35ClCN) = 5 970.820 ± 0.010 MHz, B(37ClCN) = 5 847.246 ± 0.008 MHz, eqQ(35Cl) = -83.26 ± 0.04 MHz, eqQ(37Cl) = -65.61 ± 0.04 MHz and eqQ(14N) = -3.60 ± 0.08 MHz. © 1979.
• Williams, J. R., & Kukolich, S. G. (1979). Beam maser rotational relaxation measurements on OCS. Chemical Physics, 36(2), 201-205.
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  Abstract: Rotational relaxation cross section measurements were made for J = 0, 1 and 2 rotational states of OCS using a beam maser spectrometer. Individual rotational states were selected using electrostatic fields and cross sections for scattering and relaxation of these states by polar and non-polar scattering gasses were obtained. The angular resolution was carefully controlled so that cross sections can be compared for the different rotational states. An analysis of dipolar contributions to scattering cross sections in terms of relaxation matrix elements is presented and this is consistent with some of the observed differences in pure-states cross sections. © 1979.
• Williams, J. R., & Kukolich, S. G. (1979). Variation of Br quadrupole coupling with isotopic substitution in methyl bromide. Journal of Molecular Spectroscopy, 74(2), 242-246.
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  Abstract: The J = 0 ← 1 transitions in CH379Br (I), CH381Br (II), CD379Br (III), and CD381Br (IV) were measured using a Stark-cell spectrometer constructed from C-band waveguide. High-resolution spectra yielded precise values for the bromine quadrupole coupling strength. Values obtained were eqQ(I) = -577.08 ± 0.15 MHz, eqQ(II) = -482.18 ± 0.15 MHz, eqQ(III) = -575.66 ± 0.15 MHz, and eqQ(IV) = -480.89 ± 0.15 MHz. The observed center frequencies for the J = 0 ← 1 transitions are ν0(I) = 19136.35 ± 0.03 MHz, ν0(II) = 19063.62 ± 0.03 MHz, ν0(III) = 15429.23 ± 0.03 MHz, and ν0(IV) = 15362.41 ± 0.03 MHz. A 0.26 ± 0.02% decrease in bromine quadrupole coupling is observed when the methyl group is fully deuterated. This is in agreement with, and supports interpretations given for, previous results on methyl chloride. © 1979.
• KUKOLICH, S., ALDRICH, P., READ, W., & CAMBELL, E. (1978). MICROWAVE STRUCTURE DETERMINATION AND QUADRUPOLE COUPLING MEASUREMENTS ON ACETYLENE HCN AND ETHYLENE HCN COMPLEXES. CHEMICAL PHYSICS LETTERS, 90(5), 329-331.
• Kukolich, S. G. (1978). Comments on "Rotational cooling in a seeded OCS beam". Chemical Physics, 35(1-2), 259-.
• Kukolich, S. G., Lind, G., Barfield, M., Faehl, L., & Marshall, J. L. (1978). Carbon-13 magnetic shielding from beam-maser measurements of spin-rotation interaction in acetonitrile. Journal of the American Chemical Society, 100(23), 7155-7159.
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  Abstract: The J = 1 → 0 transitions in CH313CN were observed using a beam maser spectrometer at 6-kHz line width (fwhm) and a 13C-enriched sample. The strongest component was observed with natural-abundance CH313CN. Spectra of CH313CN were obtained at higher resolution using Ramsey's method of separated oscillating fields. For CH313CN we obtain eqQN = -4224.4 ± 0.7 kHz, CN = 2.0 ± 0.4 kHz, CH = -0.6 ± 0.4 kHz, and a J = 1 → 0 transition center frequency of 18 397 783.5 ± 0.7 kHz. For CH313CN the J = 1 → 0 transition center frequency is 18 388 681.0 ± 2.0 kHz and we obtain eqQN = -4224.6 ± 1 kHz and CN = 1.9 ± 0.5 kHz. The 13C spin-rotation strength in CH313CN was determined in this study to be 3.6 ± 0.2 kHz and this leads to a value of σ⊥ = -11 ± 14 ppm. © 1978 American Chemical Society.
• Kukolich, S. G. (1977). Beam maser double resonance measurements on HDO. The Journal of Chemical Physics, 66(10), 4345-4348.
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  Abstract: High resolution measurements of hyperfine structure on the 2 20-221 transition of HDO were made with a two-cavity beam maser using the Ramsey method and using a new double resonance technique. Resonances for magnetic dipole transitions between hyperfine sublevels of the rotational states were detected by observing intensity changes in the two-cavity interference pattern for microwave rotational transitions. The linewidth (fwhm) for the magnetic dipole transitions was 1 kHz. This linewidth allows better effective resolution than the two-cavity Ramsey resonance when nozzle beams are used. Deuterium quadrupole coupling and spin-rotation interaction strengths were obtained. This double resonance technique should be useful for other small molecules, particularly for those cases where the data cannot be obtained from the microwave transitions. Copyright © 1977 American Institute of Physics.
• Williams, J. R., Casleton, K. H., & Kukolich, S. G. (1977). Measurements of T₁ and T₂ relaxation cross sections for HDO. The Journal of Chemical Physics, 66(3), 902-904.
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  Abstract: Rotational relaxation cross sections for the 220, 2 21, and superposition states of HDO were measured using a beam maser spectrometer. Scattering gases used were H2O, D2O, HDO (50%), HCl, CH3F, NH3, OCS, CO2, N2, and Ar. For HDO-NH3 scattering, pure state cross sections were much larger than the superposition state cross section. For other scattering gases, pure state cross sections were slightly larger than the superposition state cross section. Copyright © 1977 American Institute of Physics.
• Casleton, K. H., Gierke, T. D., Wang, J. H., & Kukolich, S. G. (1976). Spin-rotation measurements and magnetic shielding in CH₂CF ₂. The Journal of Chemical Physics, 64(2), 471-476.
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  Abstract: Rotational transitions 101→000, 2 12→111, 211→212, and 321→322 of 1,1 difluoroethylene were studied using a molecular beam maser spectrometer. Emission transitions were observed with 6 kHz linewidth (FWHM) and hyperfine structure due to fluorine and hydrogen interactions was resolved. The diagonal elements of the fluorine spin-rotation tensor are Maa=-13.4±3.6 kHz, Mbb=-10.94±0. 68 kHz and Mcc=-6.06 ±0.68 kHz. This data is used to determine paramagnetic contributions to the fluorine chemical shift tensor. Analysis of the data yielded line centers for the rotational transitions of 15774348 ±3 kHz for 101→-000, 26465055±5 for 212→111, and 14419906±3 kHz for 3 21→322, and 15250615±3 kHz for 2 11→212. Results of semiempirical calculations of diamagnetic contributions to the shielding tenors are presented for CH 2CF2 and other molecules. Comparisons of total shielding tensors are made for related molecules. Copyright © 1976 American Institute of Physics.
• Hackel, L. A., Casleton, K. H., Kukolich, S. G., & Ezekiel, S. (1976). Nuclear hyperfine splittings in the B-X electronic band system of ¹²⁷I₂. Chemical Physics Letters, 43(1), 104-.
• Koutcher, J. A., Larkin, R. H., Williams, J. R., & Kukolich, S. G. (1976). Rotational absorption spectrum of methylene fluoride in the 20-100 cm^-1 region. Journal of Molecular Spectroscopy, 60(1-3), 373-380.
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  Abstract: The pure rotational spectrum of CH2F2 was recorded in the 20-100 cm-1 spectral range and analyzed to obtain rotation and centrifugal distortion constants. Analysis of the data yielded rotation constants: A = 1.6392173 ± 0.0000015, B = 0.3537342 ± 0.00000033, C = 0.3085387 ± 0.00000027, τaaaa = -(7.64 ± 0.46) × 10-5, τbbbb = -(2.076 ± 0.016) × 10-6, τcccc = -(9.29 ± 0.12) × 10-7, T1 = (4.89 ± 0.20) × 10-6, and T2 = -(1.281 ± 0.016) × 10-6cm-1. © 1976.
• Williams, J. R., & Kukolich, S. G. (1976). Angular resolution and isotope studies for inversion relaxation in NH ₃. The Journal of Chemical Physics, 66(1), 251-255.
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  Abstract: Inversion relaxation cross sections for the J = 3, K = 2 upper state of NH3 were measured using a beam maser spectrometer. Scattering gases were NH3, ND3, HCl, and H2O. For NH 3-NH3 scattering the angular resolution was varied from 1.5° to 0.2° with little effect on cross sections. Cross sections for NH3 and ND3 as scattering gases were equal within experimental error. The result that beam maser cross sections are relatively independent of angular resolution is discussed. Calculated angular resolution corrections are compared with values of beam attenuation cross sections and total cross sections obtained from the present data. Comparison is made between our pure state (σI) and superposition state (σII) cross sections and recent T1 and T2 gas-cell data. Copyright © 1977 American Institute of Physics.
• Casleton, K. H., & Kukolich, S. G. (1975). Beam maser measurements of hyperfine structure in ¹⁴N ₂O. The Journal of Chemical Physics, 62(7), 2696-2699.
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  Abstract: High resolution measurements of hyperfine structure on the J=1→0 rotational transitions in 14N2O were made with a molecular beam maser spectrometer. All seven hyperfine components arising from quadrupole interactions by two nitrogen nuclei were completely resolved. This permitted determination of both quadrupole coupling constants as well as the two spin-rotation constants. Values of the best least-squares fit parameters are (eqQ)end=-776.7±1.0 kHz, (eqQ)central=-269.4±1.8 kHz, Mend=-2.35±0.20 kHz, and Mcentral=-2.90±0.26 kHz. The spin-rotation constants are used to calculate magnetic shielding parameters for the two nitrogen nuclear sites. The 1→0 rotational transition frequency is 25 123 246 kHz. Copyright © 1975 American Institute of Physics.
• Casleton, K. H., Chien, K. -., Foreman, P. B., & Kukolich, S. G. (1975). Rotational relaxation measurements on OCS using a beam maser. Chemical Physics Letters, 36(3), 308-311.
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  Abstract: Rotational relaxation cross sections are reported for J = 0, 1 and 2 rotational states of OCS using a variety of polar and non-polar scattering gases. Cross sections are reported for pure states, superposition states and total beam attenuation. Inelastic cross sections for symmetric top scattering molecules are much larger than corresponding cross sections for linear scattering molecules. Upper and lower states for both J = 0 → 1 and J = 1 → 2 transitions were selected using quadrupole or co-axial focusers. These preliminary results show differences in cross sections for different rotational states. © 1975.
• Chien, K. -., Foreman, P. B., Castleton, K. H., & Kukolich, S. G. (1975). Relaxation cross section measurements on NH₃ and lower state focussing in a beam maser. Chemical Physics, 7(1), 161-163.
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  Abstract: Scattering cross for the lower state of the J=3, K=2 inversion doublet of NH3 were measured using a beam maser spectrometer. The observed relaxation cross sections were the same as those obtained previously for the upper inversion state. These results support previous interpretations of observed relaxation cross sections for coherent superposition states. A coaxial electrostatic focusser state selector for beam maser spectroscopy which provides efficient focussing of states with a negative Stark effect is described. © 1975.
• Foreman, P. B., Chien, K. -., & Kukolich, S. G. (1975). Beam maser measurements of rotational relaxation of H₂CO. The Journal of Chemical Physics, 62(12), 4710-4714.
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  Abstract: Inelastic scattering cross sections for the upper and lower states of J=1 and J=2, K-type doublets of formaldehyde were measured using a beam maser spectrometer. Scattering gasses used were He, Ar, H2, N2, CO2, HCl, NH3, CH3F, and CF3H. Systematic variations in cross sections with the symmetry and dipole moments of scattering molecules are observed. Anderson's theory of pressure broadening, with slight modification, is used to interpret the data. This model gives reasonably good agreement with most of the observed effects. Copyright © 1975 American Institute of Physics.
• Hackel, L. A., Casleton, K. H., Kukolich, S. G., & Ezekiel, S. (1975). Observation of Magnetic Octupole and Scalar Spin-Spin Interactions in I2 Using Laser Spectroscopy. Physical Review Letters, 35(9), 568-571.
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  Abstract: Magnetic octupole and scalar spin-spin interactions have been observed in I2127 by precisely measuring (line centers located to 1 part in 1011) the hyperfine spectrum on the P(13), 43-0 line using laser-molecular-beam techniques. The values of the coupling strengths obtained from fitting the spectrum are, for the electric quadrupole, eQq′=-554 094±13 kHz and eQq′′=-2 448 025±10 kHz; for the spin-rotation, C′-C′′=186.71±0.10 kHz; for the tensor spin-spin, Dt′-Dt′′=-100.5±1.0 kHz; for the scalar spin-spin, Ds′-Ds′′=-2.72±1.0 kHz; and for the magnetic octupole, Ωm′-Ωm′′=-2.17±0.70 kHz. © 1975 The American Physical Society.
• KUKOLICH, S., & CASLETON, K. (1975). MOLECULAR ZEEMAN EFFECT IN NH3. CHEMICAL PHYSICS LETTERS, 18(3), 408-410.
• KUKOLICH, S., & FLYGARE, W. (1975). MOLECULAR G VALUES, MAGNETIC SUSCEPTIBILITIES, MOLECULAR QUADRUPOLE MOMENT, AND SPIN-ROTATION INTERACTION IN 15NH3. MOLECULAR PHYSICS, 17(2), 127-&.
• KUKOLICH, S., & WOFSY, S. (1975). N-14H3 HYPERFINE STRUCTURE AND QUADRUPOLE COUPLING. JOURNAL OF CHEMICAL PHYSICS, 52(10), 5477-&.
• Kukolich, S. G. (1975). Magnetic susceptibility anisotropy and molecular quadrupole moment in (NH3)-N-14. CHEMICAL PHYSICS LETTERS, 5(7), 401-404.
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  The molecular Zeeman effect in (NH3)-N-14 was observed using a beam maser spectrometer in a 19 kG magnetic field. The measured susceptibility anisotropy is chi perpendicular to -chi(parallel to) = -(0.37 +/- 0.04) x 10(-6) erg/gauss(2) mole. The molecular quadrupole moment along the symmetry axis is Q,, = -(2.32 +/- 0.07) x 10(-26) esu cm(2). Other molecular constants are reported.
• Kukolich, S. G. (1975). Proton magnetic shielding tensors from spin-rotation measurements on H₂CO and NH₃. Journal of the American Chemical Society, 97(20), 5704-5707.
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  Abstract: The spin-rotation tensor for H2CO was obtained from very high resolution beam maser measurements of rotational transitions. Spin-rotation tensor elements are Maa = -4.12 ± 0.36 kHz, Mbb = 2.45 ± 0.32 kHz, and Mcc = -2.10 ± 0.34 KHz in the principal axis system. These results are combined with previous molecular orbital calculations of diamagnetic shielding to obtain total absolute shielding tensor elements of σaa = 15.9, σbb = 40.7, and σcc = -1.7 ppm and an average shielding of 18.3 ppm with uncertainties of ±2 ppm or better. A similar analysis is carried out for NH3. Spin-rotation tensors and shielding tensors are given for proton and nitrogen sites with estimated accuracy better than 1 ppm. For NH3 σzz(H) = 26.5 ppm and σ(H) = 31.2 ppm. The absolute shielding scale is discussed.
• Foreman, P. B., Chien, K. -., & Kukolich, S. G. (1974). Measurements of rotational relaxation cross sections for H₂CO. Chemical Physics Letters, 29(2), 295-297.
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  Abstract: Cross sections for the 111, 110, 212, and 211 rotational states and for total beam attenuation of H2CO were measured using a beam maser spectrometer. Significant inelastic scattering in the forward direction was obtained for He and CF3H. Significant inelastic contributions were not observed using H2 as a scattering gas. Observed cross sections for the 111 state are larger than those for the 110 state. The relations of the present cross sections to various models for obtaining a low excitation temperature for the 111-110 doublet of formaldehyde in interstellar space is discussed. © 1974.
• Foreman, P. B., Chien, K. R., Williams, J. R., & Kukolich, S. G. (1974). Measurement of the dipole moment of CF₃CN. Journal of Molecular Spectroscopy, 52(2), 251-255.
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  Abstract: The Stark effect was observed for K = 0 and K = 1, J = 1 → 2 transitions in CF3CN. Measurements were made in a Stark modulated microwave spectrometer. The dipole moment obtained was μ = 1.262 ± 0.010 D. An analysis of the effects of electric field inhomogeneities on the observed Stark shifts for K = 0 and K = 1 states is included. Appropriate corrections are given for measuring linear Stark effects in a standard waveguide cell calibrated using a molecule with second-order Stark effect. © 1974.
• KUKOLICH, S. (1974). STRUCTURE AND QUADRUPOLE COUPLING MEASUREMENTS ON THE NO DIMER. JOURNAL OF MOLECULAR SPECTROSCOPY, 98(1), 80-86.
• KUKOLICH, S., NELSON, A., & , . (1974). MOLECULAR-BEAM MICROWAVE SPECTRA OF HNCO AND DNCO. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 93(25), 6769-&.
• Kukolich, S. G., Oates, D. E., & Wang, J. H. (1974). Rotational energy distribution in a nozzle beam. The Journal of Chemical Physics, 61(11), 4690-4699.
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  Abstract: The fraction of beam molecules in J =0, J = 1, and J=2 rotational states of OCS was measured as a function of pressure behind a nozzle beam source. The fractional populations were obtained from the intensities of microwave emission and absorption signals observed with a beam maser spectrometer. Total beam intensities were measured also. Large deviations from a Boltzmann rotational energy distribution were observed. The "effective rotational excitation temperature" obtained from fractional population was near 15°K for ,7=0, 40°K. for J = l, and 170°K for J =2 with 150 Torr nozzle pressure.
• Nelson, A. C., Kukolich, S. G., & Ruben, D. J. (1974). Beam maser measurement of deuterium quadrupole coupling in CD₂F₂. Journal of Molecular Spectroscopy, 51(1), 107-110.
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  Abstract: Hyperfine structure on the 220 → 313 rotational transition of CD2F2 was measured using a molecular beam maser spectrometer with 6 kHz linewidth (f.w.h.m.). The measured deuterium quadrupole coupling strength along the CD bond direction is eqzzQ = 186 ± 10 kHz. The best fit asymmetry parameter is η = -0.15 ± 0.05. Spin-rotation interaction strengths obtained from the spectrum are related to similar terms for CH2F2. The center frequency for the observed transition is 22 727 863 ± 2 kHz. © 1974.
• Ruben, D. J., & Kukolich, S. G. (1974). Beam maser measurements of distortion effects on quadrupole coupling in NH₃. The Journal of Chemical Physics, 61(9), 3780-3784.
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  Abstract: High resolution (350 Hz) measurements of hyperfine structure on the J =5, K =3 inversion transition in NH, are reported. The average nitrogen quadrupole coupling strength is -393.90k0.08 kHz. This value is in excellent agreement with a value predicted by Hougen's theory.describing distortion corrections to quadrupole coupling in NH, and does not agree with a value calculated without the correction. The line center frequency and other hyperfine structure parameters are given.
• Ruben, D. J., & Kukolich, S. G. (1974). Deuterium quadrupole coupling in formic acid. The Journal of Chemical Physics, 60(1), 100-102.
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  Abstract: The 101→ O00 and 313→3 12 transitions of HCOOD were measured using a beam maser spectrometer with 4 kHz resolution. The measurements of three completely resolved components for each of these transitions allowed an unambiguous assignment of the spectrum. The quadrupole coupling strength in the O-D bond direction is eq zzQ = 272 ±3 kHz with an asymmetry η = - 0.075 ± 0.010. Analysis of previous data on DCOOH yields a deuterium quadrupole coupling strength along the D-C bond direction of eqzzQ = 166 kHz. Copyright ©1974 American Institute of Physics.
• Wang, J. H., Levy, J. M., Kukolich, S. G., & Steinfeld, J. I. (1974). Microwave transient nutation measurements of relaxation in OCS and NH3. CHEMICAL PHYSICS, 1(2), 141-148.
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  The phenomenological Bloch equations are solved for transient nutation in optical two-level systems, using the Feynman-Vernon-Hellwarth representation, The resulting solutions display an exponentially damped oscillatory behavior, from which the relaxation times T-1 and T-2 may be derived. Transient nutation signals were observed using time-resolved microwave spectroscopy with rapid switching of applied Stark fields. Observed collision relaxation rates are (5.25 +/- 0.50) MHz/torr for OCS-OCS, (1.96 +/- 0.30) MHz/torr for OCS-He and (1.67 +/- 0.20) MHz/torr for OCS-Ar. For NH3-NH3 relaxation the rate is (23.2 +/- 3.5) MHz/torr for the (8,7) inversion line.
• Ben-Reuven, A., & Kukolich, S. G. (1973). Relaxation rates in molecular beam maser experiments. Chemical Physics Letters, 23(3), 376-380.
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  Abstract: A theoretical explanation is given of recent measurements by Kukolich, Wang and Oates on the relaxation of pure inversion states and superposition states in a molecular-beam ammonia maser spectrometer. The Feynman-Vernon-Hellwarth representation is used, combined with an impact theory of collision damping, to derive the rate equations. It is shown, in agreement with experiment, that the longitudinal-component decay rate (analogous to a T1 process in the Bloch equiations in magnetic resonance) is larger than the transverse-component decay rate (the analog of a T2 process), in contrast to the usual magnetic-resonance case. The difference between the two rates depends on the efficiency of inelastic collisions in mixing the two maser levels, and is therefore more likely to occur with polar scattering gases having appropriate energy level spacings and populations. © 1973.
• Brenner, A. R., & Kukolich, S. G. (1973). Analysis of SO₂ concentration in air by microwave spectroscopy. Analytical Letters, 6(8), 691-697.
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  Abstract: Low concentrations of SO2 IN AIR WERE MEASURED USING A Stark modulated microwave spectrometer. Measurement of the intensity of absorption lines for rotational transitions gives a quantitative measure of the concentration of specific small molecules. Concentrations of 20 ppm of SO2 in air were easily detected with a signal to noise ratio of over 20/1 with a 5 sec time constant using a straight forward sample concentration technique.
• Casleton, K. H., & Kukolich, S. G. (1973). Measurement of deuterium quadrupole coupling in CH₃OD. Chemical Physics Letters, 22(2), 331-334.
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  Abstract: K = 1 → 0 transitions in CH3OD for J = 1, 2, 3 and 4 E2-type states were measured using a beam maser spectrometer with 6 kHz linewidth (fwhm). Analysis of J = 1 and J = 2 spectra provided a deuterium quadrupole coupling strength along the O-D bond dijection of egzzQ = 303 ± 12 kHz. © 1973.
• Drouin, B., & Kukolich, S. (1973). Microwave spectra and the molecular structure of tetracarbonylethyleneiron. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 121(16), 4023-4030.
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  Microwave spectra of seven isotopomers of tetracarbonylethyleneiron were recorded using a Pulse-Beam Fourier Transform Microwave Spectrometer. Rotational transitions for a "c" dipole moment;with J'
• Drouin, B., & Kukolich, S. (1973). Molecular structure of tetracarbonyldihydroiron: Microwave measurements and density functional theory calculations. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 120(27), 6774-6780.
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  Microwave spectra of seven isotopomers of tetracarbonyldihydroiron were measured in the 4-16 GHz range using a Flygare-Balle type microwave spectrometer. Measured transitions were fit using a rigid rotor Hamiltonian with five independent distortion constants. Structural parameters from a least-squares fit to the rotational constants are r(Fe-H) = 1.576(64) Angstrom, r(Fe-Cl) = 1.815(54) Angstrom, r(Fe-C3) = 1.818(65) Angstrom, r(C1-O1) = 1.123(80) Angstrom, r(C3-O3) = 1.141(74) Angstrom, angle(H-Fe-H) = 88.0(2.8)degrees, angle(C1-Fe-C2) = 154.2(4.2)degrees, angle(C3-Fe-C4) = 99.4(4.3)degrees, angle(Fe-C1-O1) = 172.5(5.6)degrees, and angle(Fe-C3-O3) = 177.8(6.8)degrees. All of the carbonyl groups are bent slightly toward the hydrogen atoms. The least-squares-determined structural parameters are in excellent agreement with the substitution coordinates determined from the Kraitchman equations, the structural parameters calculated using density functional theory, and the previously published electron diffraction data. The C-2 upsilon molecular symmetry is consistent with the results of the microwave data and with theoretical calculations. All of the analyses show that the H atoms are separated by about 2.2 Angstrom, and this indicates that the complex is clearly a "classical dihydride" rather than an eta(2)-"dihydrogen" complex. Structural parameters obtained from a density functional theory calculation agreed with measured values to within 2%. The density functional theory analysis of the anharmonicity in the Fe-H symmetric stretching potential is shown to support the observed deuterium isotope effects observed for the hydrogen atom coordinates. The anharmonicity effects are larger for the Fe-H stretching coordinate than for the angle H-Fe-H interbond angle. The r(0)(Fe-D) bond lengths were observed to be 0.05(4) Angstrom shorter than the r(0)(Fe-H) bond lengths.
• KUKOLICH, S. (1973). MEASUREMENTS OF HYPERFINE STRUCTURE IN NH2D. JOURNAL OF CHEMICAL PHYSICS, 49(12), 5523-&.
• KUKOLICH, S., & FLYGARE, W. (1973). MOLECULAR G-VALUES MAGNETIC SUSCEPTIBILITY ANISOTROPIES SECOND MOMENT OF CHARGE DISTRIBUTION AND MOLECULAR QUADRUPOLE MOMENTS IN FORMIC ACID. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 91(10), 2433-&.
• KUKOLICH, S., & HUFFMAN, D. (1973). EPR-SPECTRA OF C60 ANION AND CATION RADICALS. CHEMICAL PHYSICS LETTERS, 182(3-4), 263-265.
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  EPR spectra of dilute solutions of cation and anion radicals produced from a nearly pure C60 sample and samples containing C60 and C70 were recorded at 9.1 GHz, near 3400 G. The measured g-value, which assigned to (C60)+, is 2.0030(2). A series of four resonances were observed for the anion radicals. The measured g-values are 2.0002 (4), 2.0006(2), 2.0009(4) and 2.0014(4). For most cases, narrow resonances with linewidth of 0.2 G or less were obtained with no apparent hyperfine structure. Three of the anion g-values are tentatively assigned to: (C60)- at g = 2.0006, (C60)3- at g = 2.0009 and (C60)5- at g = 2.0014.
• KUKOLICH, S., ALDRICH, P., READ, W., & CAMPBELL, E. (1973). MOLECULAR ZEEMAN EFFECT MEASUREMENTS ON THE ETHYLENE HCL COMPLEX. JOURNAL OF CHEMICAL PHYSICS, 79(3), 1105-1110.
• Kukolich, S. G., & Casleton, K. H. (1973). Molecular zeeman effect in NH₃. Chemical Physics Letters, 18(3), 408-410.
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  Abstract: High-resolution measurements of ΔMj = 0 inversion transitions in 14NH3 in 100 kG magnetic fields were made using a beam-maser spectrometer. The spectra show resolved splittings due to a different in molecular g-values for upper and lower inversion states with J = 3, K = 2. The observed difference in upper and lower inversion state g-values is g+(3,2)-g-(3,2) = (1.38 ± 0.08) > 62;x 10-4. © 1973.
• Kukolich, S. G., & Nelson, A. C. (1973). Chlorine quadrupole coupling in methyl chloride. Variation of quadrupole coupling strength with isotopic substitution. Journal of the American Chemical Society, 95(3), 680-682.
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  Abstract: High-resolution measurements of hyperfine structure on the J = 1 → 0 transitions in CH335Cl and CH337Cl were made using a molecular beam maser spectrometer. The measured 35Cl quadrupole coupling strength is eq Q = 74,753 ± 2 kHz and spin-rotation constant C(35Cl) = 2.4 ± 0.6 kHz. The measured 37Cl quadrupole coupling strength is eq Q = 58,910 ± 2 kHz and spin-rotation constant C(37Cl) = 1.4 ± 0.6 kHz. These results are compared with 35Cl quadrupole coupling strengths obtained for CD3Cl and CD3Cl and a systematic decrease in 35Cl quadrupole coupling is related to changes in the structure and properties of the methyl group on deuterium substitution.
• Kukolich, S. G., Ruben, D. J., Wang, J. H., & Williams, J. R. (1973). High resolution measurements of¹⁴N, D quadrupole coupling in CH₃CN and CD₃CN. The Journal of Chemical Physics, 3155-3159.
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  Abstract: A molecular beam maser spectrometer was used to measure hyperfine structure on the J = 1→0 rotational transitions in CH3CN and CD 3CN. Measured nitrogen quadrupole coupling strengths are eq aaQ(N)=-4224.4± 1.5 kHz for CH3CN and eq aaQ(N)=-4229.3± kHz for CD3CN. The deuterium quadrupole coupling strength along the C-D bond direction is eq zzQ(D)= 167.5±4.0 kHz. Nitrogen quadrupole coupling is discussed in relation to the electronic structure. Spin-rotation interaction strengths are reported. A convenient method for calculating matrix elements for hyperfine interactions in an arbitrary coupling scheme is presented.
• Kukolich, S. G., Wang, J. H., & Oates, D. E. (1973). Molecular beam maser measurements of relaxation cross sections in NH₃. Chemical Physics Letters, 20(6), 519-524.
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  Abstract: Direct measurements of scattering cross sections for NH3 in well-defined quantum states are made using a molecular beam maser spectrometer. Cross sections are compared for a pure inversion state with those for a coherent superposition state for scattering gases He, Ar, N2, N2O, NH3, CH3H and CH3CN. The cross sections are significantly larger for scattering of the pure inversion state by NH3, CF3H and CH3CN than for scattering of the superposition state. The scattering is the same for both states on non-polar gases. These cross sections are related to relaxation parameters describing transitions between rotation and inversion states. © 1973.
• Kukolich, S. G., Wang, J. H., & Ruben, D. J. (1973). Measurement of hyperfine structure in CH₂F2 by beam maser spectroscopy. The Journal of Chemical Physics, 5474-5478.
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  Abstract: High resolution measurements of hyperfine structure on the 303->2 12, 423->514, 523->616, and 61S->524 rotational transitions in CH2F2 were made using a molecular beam maser spectrometer. The components of the fluorine spin-rotation tensor obtained from the data are Maa (F)= -20.4±1.0 kHz, Mbb (F)= -4.9±0.5 kHz, and Mcc (F)= -13.1±0.5 kHz. Components of the hydrogen spin-rotation tensor are Maa (H) = 6.5±3.0 kHz, Mbb (H)= 1.0±1.4 kHz, and MK (H) = 0.3±1.3 kHz. Precise values for the rotational transition frequencies are also reported. Relations between the spin-rotation tensor and the magnetic shielding tensor for CH 2F2 are discussed. Combining the experimental spin-rotation tensor with the diamagnetic shielding tensor from the atom-dipole model, leads to the determination of the magnetic shielding tensor a aa= 407 ppm, abb, = 390 ppm, occ = 217 ppm, and aAv = 338 ppm.
• LEVY, J., WANG, J., KUKOLICH, S., & , . (1973). DIRECT OBSERVATION OF ROTATIONAL ENERGY-TRANSFER IN AMMONIA BY TIME-RESOLVED INFRARED-MICROWAVE DOUBLE-RESONANCE. CHEMICAL PHYSICS LETTERS, 21(3), 598-602.
• Levy, J. M., Wang, J. H., Kukolich, S. G., & Steinfeld, J. I. (1973). Direct observation of rotational energy transfer in ammonia by time-resolved infrared-microwave double resonance. Chemical Physics Letters, 21(3), 598-602.
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  Abstract: An N2O laser is used to pump the ground vibrational state (8,7) inversion doublet of 14NH3 while simultaneously monitoring other ground state doublets. Time-resolved rotational energy transfer signals are observed in accordance with known selection values. Absolute rates of rotational energy transfer processes are estimated. © 1973.
• Ruben, D. J., Kukolich, S. G., Hackel, L. A., Youmans, D. G., & Ezekiel, S. (1973). Laser-molecular beam measurement of hyperfine structure in the I₂ spectrum. Chemical Physics Letters, 22(2), 326-330.
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  Abstract: Very high resolution measurements of hyperfine structure on the P(13) and R(15), 43-0, 3gp0+u ← 1Σg+ transitions in iodine 127 were made using laser molecular beam spectroscopy. The observed linewidth was 300 kHz (fwhm) giving a resolution of 5 × 10-10 The observed spectrum was fitted to obtain a quadrupole coupling strength difference of ΔeQq = 1906 ± 2 MHz and a spin rotation interaction strength difference of ΔCI = 181 ± 7 kHz between the upper and lower levels of the P(13) transition. For the R (15) transition ΔeQq = 1905 ± 2 MHz and ΔCI = 167 ± 5 kHz. © 1973.
• Tanjaroon, C., Subramanian, R., Karunatilaka, C., & Kukolich, S. (1973). Microwave measurements of N-14 and D quadrupole coupling for (Z)-2-hydroxypyridine and 2-pyridone tautomers. JOURNAL OF PHYSICAL CHEMISTRY A, 108(44), 9531-9539.
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  Rotational spectra for the two tautomers (Z)-2-hydroxypyridine and 2-pytidone and their deuterated isotopomers were measured in the microwave range between 4 and 14 GHz using a pulsed beam Fourier transform microwave spectrometer. Nitrogen and deuterium quadrupole hyperfine structure was completely resolved for many of the observed transitions, and the measured N-14 quadrupole coupling tensors are quite different for these two tautomers. The eQq(cc)(N) values have opposite signs. The N-14 quadrupole coupling strengths for (Z)-2-hydroxypyridine in the principal inertial axis system are as follows: eQq(aa)(N) = -0.076(11), eQq(bb)(N) = -2.283(6), and eQq(cc)(N) = 2.359(6) MHz. The N-14 and D nuclear quadrupole coupling strengths for (Z)-2-deuteriohydroxypyridine in the principal inertial axis are eQq(aa)(N) = -0.1465(4), eQq(bb)(N) = -2.2045(4), and eQq(cc)(N) = 2.3510(4) MHz and eQq(aa)(D) = -0.0250(9), eQq(bb)(D) = 0.1699(4), and eQq(cc)(D) = -0.1449(4) MHz. The 14N quadrupole coupling strengths for 2-pyridone in the principal inertial axis system are eQq(aa)(N) = 1.496(4), eQq(bb)(N) = 1.269(4), and eQq(cc)(N) = -2.765(4) MHz. The N-14 and D nuclear quadrupole coupling strengths for 1-deuterio-2-pyridone in the principal inertial axis system are as follows: eQq(aa)(N) = 1.511(2), eQq(bb)(N) = 1.249(5), and eQq(cc)(N) = -2.759(5) MHz and eQq(aa)(D) = -0.110(7), eQq(bb)(D) = 0.354(6), and eQq(cc)(D) = -0.244(6) MHz. New, improved, experimental rotational constants were obtained for the H and D isotopomers of both tautomers. Kraitchman analysis indicates the "tautomeric" hydrogen atom is at a distance of 2.653(2) Angstrom in 2-hydroxypyridine and a distance of 2.124(1) Angstrom in 2-pyridone from the centers of mass of the two tautomers, respectively. The DFT calculated eQq(N) values for both the tautomers and the deuterated tautomers are in good agreement with the present experimental values. The Townes-Dailey model has been used to analyze the new quadrupole coupling data of the tautomers and the results are presented in terms of nitrogen atom p-orbital occupation numbers.
• Wang, J. H., & Kukolich, S. G. (1973). Beam maser measurement of ¹⁹F hyperfine structure and relation to magnetic shielding in carbonyl fluoride. Journal of the American Chemical Society, 95(13), 4138-4141.
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  Abstract: Hyperfine structure on the 110 → 111, 211 → 212, 431, → 432, and 651 → 652 rotational transitions in COF2 was observed with a molecular beam maser spectrometer. The resonance line width (fwhm) ranged from 1.5 kHz on the 111 → 110 transition to 6 kHz on the highest frequency transitions. The diagonal elements of the spin-rotation tensor obtained are Maa = -19.77 ± 0.21 kHz, Mbb = -13.46 ± 0.14 kHz, and Mcc = -7.80 ± 0.26 kHz. Magnetic shielding parameters are calculated from experimental results and comparison is made with other molecules.
• Wang, J. H., Levy, J. M., Kukolich, S. G., & Steinfeld, J. I. (1973). Microwave transient nutation measurements of relaxation in OCS and NH₃. Chemical Physics, 1(2), 141-148.
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  Abstract: The phenomenological Bloch equations are solved for transient nutation in optical two-level systems, using the Feynman-Vernon-Hellwarth representation. The resulting solutions display an exponentially damped oscillatory behavior, from which the relaxation times T1 and T2 may be derived. Transient nutation signals were observed using time-resolved microwave spectroscopy with rapid switching of applied Stark fields. Observed collision relaxation rates are (5.25 ± 0.50) MHz/torr for OCS-OCS, (1.96 ± 0.30) MHz/torr for OCS-He and (1.67 ± 0.20) MHz/torr for OCS-Ar. For NH3NH3 relaxation the rate is (23.2 ± 3.5) MHz/torr for the (8,7) inversion line. © 1973.
• Wang, J. H., Oates, D. E., Ben-Reuven, A., & Kukolich, S. G. (1973). Measurements of relaxation cross sections for NH₃ and OCS with a molecular beam maser spectrometer. The Journal of Chemical Physics, 59(10), 5268-5276.
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  Abstract: Scattering cross sections for beams of NH3 and OCS are meaured using a molecular beam maser spectrometer. The scattering gases used are NH 3, OCS, CF3H, CH3F, N2, and He. In order to determine elastic and inelastic contributions to relaxation cross sections, measurements are made for (I) scattering of pure inversion or rotational state molecules, (II) scattering of molecules in a coherent superposition state, and (III) scattering of the whole beam in a distribution of rotational states. For dipolar scattering gases the cross sections for superposition states (ωII) are significantly smaller than cross sections for pure states (ωI). A theory of the scattering is presented in terms of phenomenological Redfield parameters and the S matrix. The theoretical description of scattering is used to separate elastic and inelastic contributions to the measured cross sections.
• KUKOLICH, S. (1972). HIGH-RESOLUTION MEASUREMENTS OF HYPERFINE-STRUCTURE IN ROTATIONAL SPECTRUM OF CH3NC. JOURNAL OF CHEMICAL PHYSICS, 57(2), 869-&.
• KUKOLICH, S. G. (1972). Transistor Stark modulator. Proceedings of the IEEE, 60(1), 136-137.
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  Abstract: A transistor Stark modulator for microwave spectroscopy is reported. This is a description of a reliable Stark modulator which is easily constructed from commercial components. The output is a high quality 1000- V square wave at 10 kHz. Minor modifications permit operation to 50 kHz or higher voltages.
• KUKOLICH, S., LIND, G., BARFIELD, M., FAEHL, L., & MARSHALL, J. (1972). C-13 MAGNETIC SHIELDING FROM BEAM-MASER MEASUREMENTS OF SPIN-ROTATION INTERACTION IN ACETONITRILE. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 100(23), 7155-7159.
• KUKOLICH, S., OATES, D., & WANG, J. (1972). ROTATIONAL ENERGY DISTRIBUTION IN A NOZZLE BEAM. JOURNAL OF CHEMICAL PHYSICS, 61(11), 4686-4689.
• Kukolich, S. G., & Nelson, A. C. (1972). High-resolution molecular zeeman measurements in CH₂F ₂; observation of¹⁹F chemical shift anisotropy. The Journal of Chemical Physics, 56(9), 4475-4480.
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  Abstract: The molecular Zeeman effect was observed in méthylène fluoride using a molecular beam maser spectrometer with the cavity in a 100-kG magnetic field. This combination of high fields and high resolution (4 kHz at 22 GHz) provides unusually high resolution for these measurements. The rotational transition 3os->2i2 at 22 204 240±2 kHz was observed in emission. The measured fluorine magnetic shielding anisotropies are 2σcc- σaa-σbb=- 335.0±35 ppm and σaa-σbb = 9.0±13 ppm. Accurate susceptibility anisotropies and molecular quadrupole moments were also obtained.
• Kukolich, S. G., & Nelson, A. C. (1972). Variation of Cl quadrupole coupling with isotopic substitution in CH ₃Cl. The Journal of Chemical Physics, 57(9), 4052-4054.
• Kukolich, S. G., & Ruben, D. J. (1972). Hyperfine structure in fluoroform: A reassignment. Journal of Molecular Spectroscopy, 44(3), 607-609.
• Levy, J. M., Wang, J. H., Kukolich, S. G., & Steinfeld, J. I. (1972). Transient-nutation effects in time-resolved infrared-microwave double resonance of ammonia. Physical Review Letters, 29(7), 395-398.
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  Abstract: Transient nutation is observed in the time-resolved infrared-microwave double resonance of ammonia. This behavior is described by a Bloch equation for relaxation of the ammonia inversion levels, with an effective T2 cross section of 400 ± 50 A2. A similar effect was produced by rapidly switching the Stark field applied to the molecules, which suddenly brings them into resonance with the cw microwave radiation. © 1972 The American Physical Society.
• Daly, A. M., Daly, A. M., Douglass, K. O., Douglass, K. O., Sarkozy, L. C., Sarkozy, L. C., Neill, J. L., Neill, J. L., Muckle, M. T., Muckle, M. T., Zaleski, D. P., Zaleski, D. P., Pate, B. H., Pate, B. H., Kukolich, S. G., & Kukolich, S. G. (1971). Microwave measurements of proton tunneling and structural parameters for the propiolic acid-formic acid dimer. JOURNAL OF CHEMICAL PHYSICS, 135(15).
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  Microwave spectra of the propiolic acid-formic acid doubly hydrogen bonded complex were measured in the 1 GHz to 21 GHz range using four different Fourier transform spectrometers. Rotational spectra for seven isotopologues were obtained. For the parent isotopologue, a total of 138 a-dipole transitions and 28 b-dipole transitions were measured for which the a-dipole transitions exhibited splittings of a few MHz into pairs of lines and the b-type dipole transitions were split by similar to 580 MHz. The transitions assigned to this complex were fit to obtain rotational and distortion constants for both tunneling levels: A(0+) = 6005.289(8), B0+ = 930.553(8), C0+ = 803.9948(6) MHz, Delta(0+)(J) = 0.075(1), Delta(0+)(JK) = 0.71(1), and delta(0+)(j) = -0.010(1) kHz and A(0-) = 6005.275(8), B0- = 930.546(8), C0- 803.9907(5) MHz, Delta(0-)(J) = 0.076(1), Delta(0-)(JK) = 0.70(2), and delta(0-)(j) = -0.008(1) kHz. Double resonance experiments were used on some transitions to verify assignments and to obtain splittings for cases when the b-dipole transitions were difficult to measure. The experimental difference in energy between the two tunneling states is 291.428(5) MHz for proton-proton exchange and 3.35(2) MHz for the deuterium-deuterium exchange. The vibration-rotation coupling constant between the two levels, F-ab, is 120.7(2) MHz for the proton-proton exchange. With one deuterium atom substituted in either of the hydrogen-bonding protons, the tunneling splittings were not observed for a-dipole transitions, supporting the assignment of the splitting to the concerted proton tunneling motion. The spectra were obtained using three Flygare-Balle type spectrometers and one chirped-pulse machine at the University of Virginia. Rotational constants and centrifugal distortion constants were obtained for HCOOH center dot center dot center dot HOOCCCH, (HCOOH)-C-13 center dot center dot center dot HOOCCCH, HCOOD center dot center dot center dot HOOCCCH, HCOOH center dot center dot center dot DOOCCCH, HCOOD center dot center dot center dot DOOCCCH, DCOOH center dot center dot center dot HOOCCCH, and DCOOD center dot center dot center dot center dot HOOCCCH. High-level ab initio calculations provided initial rotational constants for the complex, structural parameters, and some details of the proton tunneling potential energy surface. A least squares fit to the isotopic data reveals a planar structure that is slightly asymmetric in the OH distances. The formic OH center dot center dot center dot O propiolic hydrogen bond length is 1.8 angstrom and the propiolic OH center dot center dot center dot O formic hydrogen bond length is 1.6 angstrom, for the equilibrium configuration. The magnitude of the dipole moment was experimentally determined to be 1.95(3) x 10(-30) C m (0.584(8) D) for the 0(+) states and 1.92(5) x 10(-30) C m (0.576(14) D) for the 0(-) states. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3643720]
• KUKOLICH, S., & NELSON, A. (1971). HIGH-RESOLUTION MOLECULAR ZEEMAN MEASUREMENTS IN CH2F2 - OBSERVATION OF F-19 CHEMICAL-SHIFT ANISOTROPY. JOURNAL OF CHEMICAL PHYSICS, 56(9), 4446-&.
• KUKOLICH, S., & PAULEY, D. (1971). THE ROTATIONAL SPECTRA AND CENTRIFUGAL-DISTORTION PARAMETERS FOR THE NNO-DF AND ONN-DF COMPLEXES. JOURNAL OF CHEMICAL PHYSICS, 90(7), 3458-3462.
• KUKOLICH, S., NELSON, A., & RUBEN, D. (1971). MOLECULAR BEAM MEASUREMENT OF HYPERFINE STRUCTURE IN FLUOROFORM. JOURNAL OF MOLECULAR SPECTROSCOPY, 40(1), 33-&.
• Kukolich, S. G. (1971). Deuterium quadrupole coupling in formyl fluoride. The Journal of Chemical Physics, 55(2), 610-612.
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  Abstract: The 101-000 rotational transition in HFCO and DFCO was recorded with a beam maser spectrometer. Hyperfine structure due to the deuterium quadrupole coupling was observed for DFCO. Analysis of the spectrum yielded the deuterium quadrupole coupling strength along the D-C bond direction of eqQ=205.± 4. kHz. This rotational transition had not been reported previously for DFCO. A comparison of deuterium quadrupole coupling strengths with force constants along the H-C bond is made according to the theory of Salem.
• Kukolich, S. G. (1971). High-resolution measurements of³⁶Cl and D quadrupole coupling in CH₂DCl and CD₃Cl. The Journal of Chemical Physics, 55(9), 4488-4493.
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  Abstract: Hyperfine structure on J=1→0 transitions in CH2D 35Cl and CD335Cl was observed with a molecular-beam maser spectrometer. Splittings arising from deuteron quadrupole coupling were completely resolved for some transitions and partially resolved in others. The 35Cl quadrupole coupling along the C-Cl bond direction was eqzzQ = 74 687.3±0.5 kHz for CH2DCl and eq zzQ = 74 573.1±0.5 kHz for CD3Cl. This is a difference of 0.15% for the 35Cl quadrupole coupling in the C-Cl bond direction. The average deuterium quadrupole coupling strength was eq zzQ= 170.8±6.0 kHz. Calculation of hyperfine structure due to four quadrupole nuclei, three of which are equivalent, is discussed.
• Kukolich, S. G. (1971). Magnetic susceptibility anisotropy and molecular quadrupole moment in ^p14NH₃. Chemical Physics Letters, 12(1), 216-.
• Kukolich, S. G. (1971). Molecular beam measurement of the magnetic susceptibility anisotropies and molecular quadrupole moment in H₂CO. The Journal of Chemical Physics, 54(1), 105-110.
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  Abstract: The molecular Zeeman effect in formaldehyde was studied using a molecular beam maser spectrometer in fields to 17 kG. The molecular resonance linewidth was 5 kHz. ΔM = 0 and Δlf=±1 transitions were observed for the 110→111 rotational transition. The measured susceptibility anisotropies (in units of 10-6 erg/G 2·mole) are 2χaaχbb- χcc = 25.4±0.2 and 2χbb-χaa- χcc= -4.1±0.15. The molecular quadrupole moment obtained from thisdata (in units of 10-25 esu·cm2) are Qaa= -0.06±0.16, Qbb=0.33±0.12, and Q cc = - 0.27±0.20. The Stark effect produced by the motion of the molecules in the magnetic field (v̄×B̄) was clearly observed.
• Kukolich, S. G. (1971). Nitrogen quadrupole coupling and spin-rotation interaction in CH₃NC. Chemical Physics Letters, 10(1), 52-55.
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  Abstract: Hyperfine structure on the J = 1→0 transition in CH3NC was observed using a molecular beam maser spectrometer with 6 kHz resolution. Molecular parameters obtained from an analysis of the spectrum are: the nitrogen quadrupole coupling strength eqQ = (488.5±1.0) kHz, the nitrogen spin-rotation strength CN = (1.45±0.5) kHz, the hydrogen-hydrogen spin-spin interaction strength DHH = (21.33±0.5) kHz and the hydrogen spin-rotation strength CH = (-0.3±0.5) kHz. © 1971.
• Kukolich, S. G., & Nelson, A. C. (1971). High resolution rotational spectra of formamide. Chemical Physics Letters, 11(3), 383-384.
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  Abstract: Hyperfine structure on the 101 → 000 and 514 → 515 rotational transitions in NH2CHO was measured using a molecular beam maser spectrometer with 8 kHz resolution. The nitrogen quadrupole coupling tensor in the principal inertial axis system was determined. The values are eQqaa = 1960 ± 2 kHz; eQqbb = 1888 ± 3 kHz and eQqcc = -3848 ± 4 kHz. Accurate values for the center frequencies for the rotational transitions were found to be 21 207 432 kHz for the 101 → 000 transition and 23 081 205 kHz for the 514 → 515 transition. One of the nitrogen spin-rotation parameters was also determined: C(514) - C(515) = 1.2 ± 0.6 kHz. © 1971.
• Kukolich, S. G., & Ruben, D. J. (1971). Measurement of H₂CO hyperfine structure with a two-cavity maser. Journal of Molecular Spectroscopy, 38(1), 130-135.
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  Abstract: Hyperfine structure on the 110 → 111 rotational transition in H2CO was measured using a two-cavity maser spectrometer with 0.3 kHz resolution. The measured spin-rotation constants are C(110) = -0.80 ± 0.05 kHz and C(111) = -3.07 ± 0.05 kHz. The hydrogen spin-spin interaction strength is D = 17.74 ± 0.10 kHz. The line center is at 4 829 659.89 ± 0.12 kHz. Properties of the beam source and computer line resolving methods are discussed briefly. © 1971.
• Kukolich, S. G., Nelson, A. C., & Ruben, D. J. (1971). Molecular beam measurement of hyperfine structure in fluoroform. Journal of Molecular Spectroscopy, 40(1), 33-39.
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  Abstract: The J = 1 → 0 transition in CF3H and CF3D was observed using a molecular beam maser spectrometer. Typical resonance linewidths were 6 kHz (F.W.H.M.). Hyperfine structure due to deuterium quadrupole coupling, spinrotation and spin-spin interactions was resolved. The strength of the deuterium quadrupole coupling along the bond axis is eqQ = 170.8 ± 2.0 kHz. Fluorine and hydrogen spin-rotation interaction strengths were obtained. © 1971.
• Kukolich, S. G., Nelson, A. C., & Yamanashi, B. S. (1971). Molecular-beam microwave spectra of HNCO and DNCO. Journal of the American Chemical Society, 93(25), 6769-6771.
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  Abstract: Deuteron quadrupole coupling in DNCO was obtained from splittings of the 101 rotational state. The measured quadrupole coupling strength for the 101 rotational state is eqQ(101) = 53.6 ± 0.2 kHz, which leads to a value along the D-N bond eqQDN = 345 ± 2 kHz. Hyperfine splittings were observed using a molecular-beam maser spectrometer with 6-kHz resolution. The nitrogen quadrupole coupling strengths were eq/Q(101) = 2123.0 ± 1.0 kHz for DNCO and eqQ(101) = 2052.7 ± 1.0 kHz for HNCO. High-precision values for the line-center frequencies and spin-rotation constants are also reported.
• Kukolich, S., & Sickafoose, S. (1971). Microwave spectrum of the (NO)-N-15-O-16-(NO)-N-15-O-16 dimer. MOLECULAR PHYSICS, 89(6), 1659-1661.
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  The microwave transitions for the ((NO)-N-15)(2) dimer were reinvestigated following a report by McKellar et al. (1995, Molecular Physics, 86, 273) of a discrepancy between a previously measured microwave transition frequency and the corresponding frequency calculated from their molecular constants. The present microwave measurements confirm the previous observation of a rotational transition at 11 159.297(4) MHz, but this transition is apparently not due to the cis N-N bonded NO dimer, since a mixture of (NO)-N-15 in argon gas is required for observation of the 11 159.297 MHz transition. A new doublet was located at 11 128.434(4) MHz and this transition is now assigned to the 3(03)
• KUKOLICH, S. (1970). MEASUREMENT OF HYPERFINE STRUCTURE OF J=3 K=2 INVERSION LINE OF N14H3. PHYSICAL REVIEW, 138(5A), 1322-&.
• Kukolich, S. G. (1970). Magnetic susceptibility anisotropy and molecular quadrupole moment in ¹⁴NH₃. Chemical Physics Letters, 5(7), 401-404.
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  Abstract: The molecular Zeeman effect in 14NH3 was observed using a beam maser spectrometer in a 19 kG magnetic field. The measured susceptibility anisotropy is χ⊥-χ∥ = - (0.37 ± 0.04) × 10-6 erg/gauss2 mole. The molecular quadrupole moment along the symmetry axis is Q∥ = ∼ (2.32 ± 0.07) × 10-26 esu cm2. Other molecular constants are reported. © 1970.
• Kukolich, S. G., & Flygare, W. H. (1970). The molecular Zeeman effect in PH₂D and PHD₂ and the molecular g-values, magnetic susceptibilities, and molecular quadrupole moment in PH₃. Chemical Physics Letters, 7(1), 43-46.
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  Abstract: The Zeeman effect was observed for two rotational transitions in PH2D and two rotational transitions in PHD2. The combined results were analyzed to determine the ratio of g-value to rotational constant parallel and perpendicular to the symmetry axis in PH3. The results are g∥/G∥ = - (0.0279 ± 0.0015) × × 10-11 sec and g⊥/G⊥ = (0.0128 ± 0.0012) × 10-1 sec. The magnetic susceptibility anisotropy was determined to be χ∥-χ⊥ = - (2.7 ± 0.8) × 10-6 erg/G2 mole. The molecular quadrupole moment is Q″ = = - (2.1 ± 1.0) × 10-26 esu cm2. The diagonal elements of the diamagnetic, paramagnetic and total susceptibility tensors and the second moments of the electronic charge distribution are given and compared to NH3. © 1970.
• Kukolich, S. G., & Wopsy, S. C. (1970). ¹⁴NH₃ hyperfine structure and quadrupole coupling. The Journal of Chemical Physics, 52(10), 5482-5483.
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  Abstract: Hyperfine structure on the inversion transition for rotational states J-K=2-1, 3-1, 4-2, 4-4, and 5-5 was measured with a high-resolution beam maser spectrometer. Variations of nitrogen quadrupole coupling strength were observed for different rotational states. Derivatives of quadrupole coupling strength with respect to molecular coordinates are given. Additional spin-spin and spin-rotational terms are present for K=1 states. These terms are compared for J-K= 1-1, 2-1, and 3-1 states. A more complete specification of the nitrogen and hydrogen spin-rotation tensors is obtained with the new data.
• SHEA, J., & KUKOLICH, S. (1970). THE ROTATIONAL SPECTRUM AND MOLECULAR-STRUCTURE OF THE FURAN-HCL COMPLEX. JOURNAL OF CHEMICAL PHYSICS, 78(6), 3545-3551.
• KUKOLICH, S. (1969). ALTERNATING C-C BOND LENGTHS IN GAS-PHASE (BENZENE)CHROMIUM TRICARBONYL. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 117(20), 5512-5514.
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  The microwave rotational spectrum of ([1,2-D-2]benzene)chromium tricarbonyl was measured in the 4-12 GHz range using a Flygare-Balle-type spectrometer. This spectrum contains transitions due to two different structural isomers of this complex. These results are interpreted in terms of a reduction of the symmetry of benzene to C-3v due to interactions with the Cr(CO)(3) moiety. One structural isomer (isomer E) occurs when the deuterium atoms are at the ends of a ''long'' C-C bond, the other (isomer S), when the deuterium atoms are at the ends of a ''short'' C-C bond. The data indicate a difference of 0.016 Angstrom in adjacent benzene C-C bond lengths in this complex.
• KUKOLICH, S. (1969). BEAM MASER SPECTROSCOPY ON J=1-]2, K=1, AND K=0 TRANSITIONS IN CH3CN AND (CH3CN)-C-13. JOURNAL OF CHEMICAL PHYSICS, 76(1), 97-101.
• KUKOLICH, S. (1969). MEASUREMENT OF MOLECULAR G VALUES IN H2O AND D2O AND HYPERFINE STRUCTURE IN H2O. JOURNAL OF CHEMICAL PHYSICS, 50(9), 3751-&.
• KUKOLICH, S., WANG, J., & OATES, D. (1969). MOLECULAR-BEAM MASER MEASUREMENTS OF RELAXATION CROSS-SECTIONS IN NH3. CHEMICAL PHYSICS LETTERS, 20(6), 519-524.
• Kukolich, S. G. (1969). Erratum: Hyperfine structure in NH₂D (The Journal of Chemical Physics (1968) 49 (5523)). The Journal of Chemical Physics, 50(10), 4601-.
• Kukolich, S. G. (1969). Measurement of the molecular g values in H₂O and D₂O and hyperfine structure in H₂O. The Journal of Chemical Physics, 50(9), 3751-3755.
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  Abstract: Individual components of the Zeeman transitions in the rotational spectrum of H2O and D2O were resolved in fields of 25-30 kG. This allowed determination of the g values with greater accuracy than previous measurements. The g values obtained for H2O were g(523) =0.6959±0.001 and g(616) =0.6565± 0.001. The g values obtained for D2O were gaa=0.3233±0.001, g cc= 0.3580±0.001, and gcc=0.3226±0.001. Analysis of the combined results indicates that the g values for H2O are positive and that the values are gaa=0.6650±0.002, g bb= 0.7145±0.002, and gcc=0.o465±0.002. Hyperfine structure on the 616-523 transition in H 2O was observed in a maser spectrometer, and the spin-rotation and spin-spin coupling constants were obtained. The measured value of the rotational transition frequency was 22 235 079.85±0.05 kHz. The magnetic susceptibility anisotropies and molecular quadrupole moments were determined in H2O.
• Kukolich, S. G. (1969). Measurements of deuterium quadrupole coupling in formic acid. The Journal of Chemical Physics, 51(50), 358-360.
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  Abstract: The 101-000 rotational transition was observed in HCOOH, HCOOD, and DCOOH using a maser spectrometer. Quadrupole hyperfine structure was completely resolved in HCOOD and DCOOH. The measured quadrupole coupling strength along the OD-bond direction was eqQ=391 kHz and HCOOD and eqQ= 249 kHz along the DC-bond direction in DCOOH. These coupling constants and the deuterium quadrupole coupling in NH2D are compared with the corresponding force constants and the results are in fairly good agreement with the theory of Salem.
• Kukolich, S. G., & Flygare, W. H. (1969). Molecular g values, magnetic susceptibility anisotropies, second moment of the charge distribution, and molecular quadrupole moments in formic acid. Journal of the American Chemical Society, 91(10), 2433-2437.
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  Abstract: The high-field rotational Zeeman effect has been observed in formic acid. The molecular g values and anisotropies in the magnetic susceptibilities are gaa = -0.2797 ± 0.006, gbb = -0.0903 ± 0.0006, gcc = -0.0270 ± 0.0006, 2χaa - χbb - χcc = (3.4 ± 0.5) × 10-6 erg/(G2 mole), and 2χbb - χaa - χcc = (9.4 ± 0.3) × 10-6 erg/(G2 mole). Only the relative signs of the g values are determined experimentally. However, by comparing the calculated molecular quadrupole moments (for both all positive and all negative g values) with known values for other similar molecules, the above negative signs are conclusively assigned. The molecular quadrupole moments are Qaa = -(5.3 ± 0.4) × 10-26 esu cm2, Qbb = +(5.2 ± 0.4) × 10-26 esu cm2, and Qcc = +(0.1 ± 0.4) × 10-26 esu cm2. The a axis is nearly along a line connecting the two oxygen atoms, and this axis makes an angle of 31.6° with the C=O bond direction. The b axis is also in the OCO plane. The diagonal elements in the total magnetic susceptibility tensor are χaa = -(18.8 ± 0.8) × 10-6 erg/(G2 mole), χbb = -(16.8 ± 0.8) × 10-6 erg/(G2 mole), and χcc = -(24.2 ± 0.8) × 10-6 erg/(G2 mole). The diagonal elements in the paramagnetic susceptibility tensor are χaap = (28.8 ± 0.1) × 10-6, χbbp = (106.5 ± 0.1) × 10-6, and χccp = 017.2 ± 0.1) × 10-6 all in units of erg/(G2 mole). The diagonal elements in the second moment of the electronic charge distribution are 〈a2〉 = (26.6 ± 0.3) × 10-16 cm2, 〈b2〉 = (7.7 ± 0.3) × 10-16 cm2, and 〈c2〉 = (3.5 ± 0.2) × 10-16 cm2.
• BUMGARNER, R., CHOE, J., KUKOLICH, S., & BUTCHER, R. (1968). HIGH-RESOLUTION SPECTROSCOPY OF THE V6 AND V8 BANDS OF FORMIC-ACID. JOURNAL OF MOLECULAR SPECTROSCOPY, 132(1), 261-276.
• Drouin, B., Drouin, B., Lavaty, T., Lavaty, T., Cassak, P., Cassak, P., Kukolich, S., & Kukolich, S. (1968). Measurements of structural and quadrupole coupling parameters for bromoferrocene using microwave spectroscopy. JOURNAL OF CHEMICAL PHYSICS, 107(17), 6541-6548.
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  Rotational spectra for two isotopomers of bromoferrocene were measured using pulsed-beam Fourier transform microwave spectroscopy. Transitions were observed for the Br-79 and Br-81 isotopomers in the 5-9 GHz range. Rotational constants and the quadrupole coupling tensors were obtained from the data. The rotational constants and quadrupole coupling parameters for Br-79 are A=1272.110(1), B=516.1125(2), C=441.3775(2), eQq(aa)=267.16(3), eQq(ab)=-409.81(4), and eQq(bb)=21.49(4), and those for Br-81 are A=1271.045(4), B=510.0079(2), C=436.7687(2), eQq(aa)=225.40(6), eQq(ab)=-341.62(4), and eQq(bb)=15.65(4). The measured rotational constants were used to determine the following structural parameters of bromoferrocene: r(Fe-(C5H5))=1.63(2), r(Fe-(C5H4Br))=1.67(3), r(C-Br)=1.875(11), and r(C-C)=1.433(1) Angstrom. The values of the quadrupole coupling parameters in the principal quadrupole axis systems and the C-Br bond axis systems are compared with similarly derived parameters for chloroferrocene, chlorobenzene, and bromobenzene. Previous data for chloroferrocene has been reanalyzed to obtain refined quadrupole parameters. (C) 1997 American Institute of Physics. [S0021-9606(97)03241-8].
• Kukolich, S. G. (1968). Hyperfine structure of N15H3. Physical Review, 172(1), 59-63.
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  Abstract: Hyperfine structure of the inversion transition for the J-K=4-4,5-5,6-6,and7-7 rotational states of N15H3 was measured with a two-cavity maser spectrometer. Previous data on the J-K=2-2 state and these new data are analyzed including the nitrogen I→N•J→ term, the hydrogen I→•J→ term, the hydrogen-nitrogen spin-spin interaction, the hydrogen-hydrogen spin-spin interaction, and a scalar electron-coupled spin-spin interaction. For the J-K=2-2,4-4,5-5,and 7-7 states a consistent set of coupling strengths are found such that the calculated frequencies agree with the data to within the experimental accuracy. There are still large discrepancies between calculated and experimental frequencies for the J-K=1-1,3-3, and 6-6 states. © 1968 The American Physical Society.
• Kukolich, S. G. (1968). Measurements of Hyperfine Structure in NHJD. The Journal of Chemical Physics, 5464-5472.
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  Abstract: Hyperfine structure on the 414-404 rotation-inversion transition in NH2D was measured with a twocavity maser spectrometer with 350-Hz linewidth. A reasonably good fit to the observed transitions is obtained by including the nitrogen quadrupole interaction, the nitrogen spin-rotation interaction, the deuteron quadrupole interaction, the deuteron spin-rotation interaction, and the nitrogen-deuteron spinspin interaction in the Hamiltonian. The values of the coupling constants obtained are: for the 4u state (eqJQ)N=-1895.65±0.7 kHz, (eqJQ) D=-75.78±0.7 kHz, and for the 4 state (eqJQ)N=- 1811.55± 0.7 kHz, (eqjQ)i3= -80.13±0.7 kHz, and for the values of the other parameters averaged over these states CN = 5.027±0.18 kHz, CD=- 2.33±0.18 kHz, and DND=0. 307±0.70 kHz. The rotation-inversion frequency for this transition is 25 023 794.706±0.07 kHz.
• KUKOLICH, S. (1967). MEASUREMENT OF AMMONIA HYPERFINE STRUCTURE WITH A 2-CAVITY MASER. PHYSICAL REVIEW, 156(1), 83-&.
• Kukolich, S. G. (1967). Measurement of ammonia hyperfine structure with a two-cavity maser. Physical Review, 156(1), 83-92.
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  Abstract: Hyperfine structure of the J-K=1-1,2-2,3-3, and 3-2 inversion transitions in N14H3 and the 1-1, 2-2, and 3-3 transitions in N15H3 has been measured with a two-cavity maser spectrometer. This device employs Ramsey's method of separated oscillating fields to obtain a molecular resonance linewidth of 350 cps. The theory of Gunther-Mohr et al. and of Gordon has been extended to include all terms off-diagonal in F1IN+J in an attempt to explain some discrepancies between the previous theory and our measurements. The interactions included in this treatment are the nitrogen quadrupole interaction, the nitrogen IN•J interaction, the hydrogen I • J interaction, the hydrogen-nitrogen spin-spin interaction, and the hydrogen-hydrogen spin-spin interaction. The strengths of these interactions are treated as adjustable parameters in least-squares fit programs which determine the parameters by fitting the experimental data. There are still significant deviations between theory and experiment for the 1-1, 3-3, and 3-2 transitions of N14H3 and for the 1-1, 2-2, and 3-3 transitions of N15H3. The largest discrepancies occur for the N14H3 3-2 transition and the 1-1, 2-2, and 3-3 transitions in N15H3 where the quadrupole interaction vanishes. The discrepancies are greater than 1 kHz in these cases. According to the theory, pairs of satellites of the N15H3 2-2 transition should occur at the same frequency, and these are all split by 4 kHz. In addition, the values of the N15H3 coupling parameters do not agree with theory. © 1967 The American Physical Society.
• Kukolich, S. G., & Billman, K. W. (1967). Square-wave phase modulation in Ramsey-type molecular beam resonance experiments. Journal of Applied Physics, 38(4), 1826-1830.
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  Abstract: Square-wave phase modulation of the microwave signal which induces transitions allows one to measure velocity-dependent frequency shifts in Ramsey resonance experiments. The output signal from the molecular beam apparatus is demodulated by a synchronous detector operating in phase with the modulation. This output is proportional to the derivative of the transition probability and provides the usual resonance signal which is used in a servo loop to keep a harmonic of a voltage tunable crystal oscillator on the central peak of the resonance. A quadrature synchronous detector operating 90° out of phase with the modulating signal provides a measure of any velocity-dependent frequency shifts. Such shifts arise when there is a phase difference between the oscillating fields or when an electric field applied to a magnetic system produces a v×ε shift. We have theoretically and experimentally demonstrated that this quadrature signal is proportional to the phase difference between the microwave cavities of a Ramsey apparatus with the in-phase signal constrained at zero. We have also shown that the sensitivity of the quadrature system depends on the width of the available velocity distribution. © 1967 The American Institute of Physics.
• BUMGARNER, R., & KUKOLICH, S. (1965). MICROWAVE-SPECTRA AND STRUCTURE OF HI-HF COMPLEXES. JOURNAL OF CHEMICAL PHYSICS, 86(3), 1083-1089.
• Kukolich, S. G. (1965). Measurement of hyperfine structure of the J=3, K=2 inversion line of N14H3. Physical Review, 138(5A), A1322-A1325.
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  Abstract: The magnetic hyperfine structure of the J=3, K=2 inversion line of N14H3 has been measured in a maser spectrometer employing the method of separated oscillating fields. The molecular-resonance linewidth of this system is 350 cps at 23 kMc/sec. The measured frequencies of the 3-2 inversion-line components are (in cycles/sec): 22 834 247 980±50, 22 834 209 990±50, 22,834,207,230±50, 22 834 185 130±20, 22 834 163 020±50, 22 834 160 270±50, 22 834 122 270±50. The pairs of lines adjacent to the main line were unresolved previously. © 1965 The American Physical Society.

Others

• KUKOLICH, S., & SHEA, J. (1986). THE MICROWAVE-SPECTRUM AND MOLECULAR-STRUCTURE OF THE FURAN ARGON COMPLEX. JOURNAL OF CHEMICAL PHYSICS.
• KUKOLICH, S. (1973). STRUCTURE OF THE NO DIMER. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY.