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

The infrared Fourier transform spectrum of the S-H stretching fundamental band of (CH3SH)-C-12-S-32 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 Delta K = +1 and Delta K = -1 sub-bands present, the assignments are well determined fromground-state combination difference relations. The identified sub-bands access S-H stretching ground torsional substates fromK' = 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 vibrationalwavenumber for the S-H stretch mode is found to be 2603.5 cm(-1). [GRAPHICS] .