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

Published

December 1, 2002

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, D_J = 1.4424(7) kHz and D_JK = 13.674(2) kHz. The other state observed has a smaller B of 1140 580(1) MHz but requires a negative D_J = -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 C_2v 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 M_j = 0 and one having M_j = 1, M_j 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

Pub Type

Journals

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 C₆H₆-H₂S dimer and Comparisons to C₆H₆-H₂O Dimer, Journal of Chemical Physics (Accessed April 30, 2024)