SPECTRA AND STRUCTURES OF SILICON-CONTAINING COMPOUNDS .20. RAMAN ANDINFRARED-SPECTRA, CONFORMATIONAL STABILITY, VIBRATIONAL ASSIGNMENT AND AB-INITIO CALCULATIONS OF METHYLVINYLDIFLUOROSILANE

The Raman (3100-10 cm(-1)) and infrared (3100-40 cm(-1)) spectra of me thylvinyldifluorosilane, CH2CHSiF2CN3, were recorded for the gas and s olid. Additionally, the Raman spectrum of the liquid was recorded and qualitative depolarization values were obtained. The observed bands in the fluid states are assigned on the basis of the more stable gauche (antiperiplanar) conformer where one of the fluorine atoms is eclipsin g the double bond and the less stable cis (synplanar) conformer. Howev er, in the annealed crystalline solid, only the cis conformer remains. A complete vibrational assignment is proposed for both conformers bas ed oh infrared Band contours, Raman depolarization data, group wavenum bers and normal coordinate calculations. The experimental stability, b arriers to internal rotation, and fundamental vibrational wavenumbers are compared with those obtained from the ab initio calculations emplo ying the RHF/3-21G, RHF/6-31G* and MP2/6-31G* basis sets and to the c orresponding quantities obtained for some similar molecules.