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Rotational Spectrum of the Weakly Bonded C6H6-H2S dimer and Comparisons to C6H6-H2O Dimer

Published

Author(s)

E Arunan, T Emilsson, H S. Gutowsky, Gerald T. Fraser, G de Oliveira, C E. Dykstra

Abstract

Tow symmetric-top, δJ = 1 progressions were observed for the C6H6-H2S dimer using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants for C6H6-H2S are B = 1168.53759(5) MHz, DJ = 1.4424(7) kHz and DJK = 13.674(2) kHz. The other state observed has a smaller B of 1140 580(1) MHz but requires a negative DJ = -13.80(5) kHz and higher order (H) terms to fit the data. Rotational spectra for the isotopomers C6H6-H234S, C6H6-H233S, C^H6-HDS, C6H6-D2S and 13CC5H6-H2S were also obtained. Except for the dimer with HDS, all other isotopomers gave two progressions like the most abundant isotopomer. Analysis of the ground-state data indicates that H2S is located on the C6 axis of the C6H6 with a c.m.(C6H6)-S distance of 3.818 . The angle between the α axis of the dimer and the C2v axis of the H2S is determined to be 28.5 . The C6 axis of C6H6 is nearly coincident with a axis of the dimer. Stark measurements of the two states led to dipole moments of 1.14(2) D for the ground state and 0.96(6) D for the other state. A third progression was observed for C6H6-H2S which appear to have K not equal to} 0 lines split by several MHz, suggesting a non-zero projection of the internal rotation angular momentum of H2S on the dimer a axis. Observation of three different states suggests that the H2S is rotating in a nearly spherical potential leading to three internal rotor states, two of which have Mj = 0 and one having Mj = 1, Mj being the projection of internal rotational angular momentum on to the a axis of the dimer. The nuclear quadrupole hyperfine constant of 33S nucleus in the dimer is determined for the two symmetric-top progressions and they are -17.1 MHz for the ground state and -8.4 MHz for the other state, consistent with the assignment to two different internal-rotor states. The rotational spectrum of the C6H6-H2S complex is very different from that of the C6H6-H2O complex. Model potential calculations predict small barriers of 227 cm-1, 121 cm-1 and 356 cm-1 for rotation about a, b, and c axes of H2S, respectively, giving qualitative support for the experimental conclusion that H2S is effectively freely rotating in a nerly spherical potential. For the C6H6-H2O complex, the corresponding barriers are 365 cm-1, 298 cm-1 and 590 cm-1.
Citation
Journal of Chemical Physics
Volume
117
Issue
No. 21

Keywords

benzene, complex, microwave, spectroscopy, structure

Citation

Arunan, E. , Emilsson, T. , Gutowsky, H. , Fraser, G. , de Oliveira, G. and Dykstra, C. (2002), Rotational Spectrum of the Weakly Bonded C<sub>6</sub>H<sub>6</sub>-H<sub>2</sub>S dimer and Comparisons to C<sub>6</sub>H<sub>6</sub>-H<sub>2</sub>O Dimer, Journal of Chemical Physics (Accessed July 23, 2024)

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Created November 30, 2002, Updated October 12, 2021