5314027759

POSTER SESSION. H12

THE i/,, U2, 1/7 AND 1* BANDS SYSTEM OF METHYL SILANE

CHANGHONG XIA AND GEOFFREY DUXBURY , Department oj Physics and Applied Physics, Unwersity oj Strathclyde, Glasgow,

G4 ONG, Scotland, UK.

Methyl Silane, CH3S1H3, has been studied extensively by microwave spectroscopy^a , sińce the hindered internal rotation about the C-Si axis of the methyl and silane groups is a pro-totypical example of internal rotation in a symmetric rotor molecule. However, although the lowest frequency degenerate bending vibration, i/\2, has been studied in considerable detail at high resolution ^{1 2 3}, the bands in the CH and SiH stretching regions have only been studied at moderate resolution^c. By using the high resolution Bruker Fourier transform spectrometer of the NERC molecular spectroscopy facility at the Rutherford Appleton Laboratory we have been able to record spectra with a resolution of 0.0017 cm^-1 at room temperaturę and 200 K, and by the use of collisional cooling, with a resolution of 0.005 cm"¹ at 100K. This has enabled to to indentify the torsional hot band structure, to com-plete the rotational analysis of both band systems, and to almost completely resolve the torsional splittings of the ro-vibrational lines. If the torsional splitting is neglected, the pattern of the 3 /nn bands resembles that of the A1:E structure of the 1/2 and ^ bands of CHsF**, whereas the 5 /jm system more.closely resembles the strongly coupled A\/E u2 and u*, bands of CH3F. However once the torsional structure is revealed this theory needs to be extended as indicated by Moazzen-Ahmadi et al. We have chosen to work in the free rotor basis^f , sińce it facilitates the treatments of vibrational coupling at both ends of the molecule. In addition we have been able to show that the splitting of the v\ band into two is almost certainly due to Fermi resonance, and not to the mechanisms previously proposed which are summarised in the paper by Duncan et al.

1

°N. MoazZEN-Ahmadi, I. Ozier. E.H. WlSHNOW, and H.P. Gush, J. Mol. Spectrosc.no,

2

516 (1995).

3

N. Moazzen-Ahmadi, I. Ozier, and W.L. Meerts, J. Mol. Spectrosc. 137, 166 (1989). ^eJ.L. Duncan, A.M. F ergu SON, and D.C. McKean, J. Mol. Spectrosc. 168, 522 (1994). ^dC. t)l LAURO and I.M. Mills, J. Moi Spectrosc. 21,386 (19665). ^eG. PELTZ, P. Mittler, K.M.T. Yamada, and G. Winnewisser, J. Mol. Spectrosc. 156, 3906 (1992).