FTIR synchrotron spectroscopy of the S-H stretching fundamental of the 12CH332SH species of methyl mercaptan

• Published in: Molecular physics 2018-12, Vol.116 (23-24), p.3554-3563
• Main Authors: Lees, R. M., Xu, Li-Hong, Twagirayezu, S., Perry, D. S., Dawadi, M. B., Billinghurst, B. E.
• Format: Article
• Language: English
• Subjects: Far infrared radiation; Fourier transforms; infrared spectra; internal rotation; Methyl mercaptan; Power series; S-H stretching band; Stretching; Synchrotron radiation; Torsion; torsion-vibration interactions; Wavelengths
• ISSN: 0026-8976; 1362-3028
• DOI: 10.1080/00268976.2018.1451931

The infrared Fourier transform spectrum of the S-H stretching fundamental band of 12 CH 3 32 SH has been recorded using synchrotron radiation at the far-infrared beamline of the Canadian Light Source in Saskatoon. The S-H stretch is a hybrid band predominantly of perpendicular b-type with a small parallel a-component. With both ΔK = +1 and ΔK = −1 sub-bands present, the assignments are well determined from ground-state combination difference relations. The identified sub-bands access S-H stretching ground torsional substates from K′ = 0-14 for A and E torsional species. The substate origins have been obtained by expanding the term values in J(J + 1) power series, and have been fitted to a simple 6-parameter Fourier Hamiltonian to deduce the torsional energies. The oscillation amplitude of the S-H stretching torsional curves is 0.547 cm − 1 compared to 0.653 cm − 1 for the ground state, implying an increase on the order of 6.9% in the torsional barrier height. The vibrational wavenumber for the S-H stretch mode is found to be 2603.5 cm − 1 .