Speaker
Dr
Ronald M. Lees
(Physics Dept., University of New Brunswick)
Description
The Fourier transform infrared spectra of the lower infrared vibrational bands of CH$_{3}$SH have been investigated from 650 to 1200 cm$^{-1}$ at 0.001 cm$^{-1}$ resolution employing synchrotron radiation at the Canadian Light Source in Saskatoon. The relative band strengths and structures are remarkably different from those for the analogous CH$_{3}$OH relative, with the CSH bend being very weak and both the in-plane and out-of-plane CH$_{3}$ rocks being strong with comparable intensities. The CSH bend has parallel $a$-type character with no detectable $b$-type component. The out-of-plane CH$_{3}$ rock is a purely $c$-type perpendicular band, whereas the in-plane rock around is of $a$/$b$ character. The $K$-reduced $v_{t}$ = 0 sub-state origins for the CSH bend follow the normal oscillatory torsional pattern as a function of $K$ with an amplitude of 0.362 cm$^{-1}$, as compared to 0.653 cm$^{-1}$ for the ground state and 0.801 cm$^{-1}$ for the C-S stretching mode. The torsional energy curves for the out-of-plane rock are also well-behaved but are inverted, with an amplitude of 1.33 cm$^{-1}$. In contrast, the sub-state origins for the in-plane rock do not display a clear oscillatory structure but are scattered over a range of about 2 cm$^{-1}$, with indications of some significant perturbations. Our sub-band assignments extend up to about $K$ = 10 for all the modes and are well-determined from GSCD relations, particularly for the $a$/$b$ in-plane rock for which $\Delta$$K$ = 0, +1 and $-$1 transitions are all observed.
Author
Dr
Ronald M. Lees
(Physics Dept., University of New Brunswick)
Co-authors
Dr
Brant E. Billinghurst
(Canadian Light Source)
Dr
Li-Hong Xu
(Physics Dept., University of NB)
