2017 CAP Congress / Congrès de l'ACP 2017

FTIR Synchrotron Spectroscopy of the S-H Stretching Band of Methyl Mercaptan – An Interstellar and Biogenic Molecule

1 Jun 2017, 11:45

15m

Botterell B147 (Queen's University)

Industrial and Applied Physics / Physique industrielle et appliquée (DIAP-DPIA) R2-1 Applied Physics and Instrumentation (DIMP/DIAP) | Physique appliquée et instrumentation (DPIM/DPIA)

Speaker

Dr Ronald M. Lees (Physics Dept., University of New Brunswick)

Description

The infrared Fourier transform spectrum of the S-H stretching fundamental band of CH${}_3$SH at 2604 cm${}^{-1}$ has been recorded using synchrotron radiation at the FIR beamline of the Canadian Light Source in Saskatoon. This band is an order of magnitude weaker than the corresponding O-H stretch of methanol, with a very different structure. It is a hybrid band predominantly of perpendicular $b$-type, with a smaller parallel $a$-component. With both $\mathrm{\Delta }$$K$ = +1 and $\mathrm{\Delta }$$K$ = -1 sub-bands present, the assignments are well-determined from ground-state combination relations, but are complicated by the presence of many $J$-localized perturbations. Upper-state term values have been determined for $K$ = 0-14, and the substate origins have been fitted to a Fourier model. The oscillation amplitude of the torsional curves is 0.545 cm${}^{-1}$ compared to 0.652 cm${}^{-1}$ for the ground state, indicating a reduction of the order of 16% in the torsional barrier height $V_3$.