SPECTRA AND STRUCTURE OF SILICON-CONTAINING COMPOUNDS .16. INFRARED AND RAMAN-SPECTRA, CONFORMATIONAL STABILITY, AB-INITIO CALCULATIONS, R(0) STRUCTURE AND VIBRATIONAL ASSIGNMENT FOR ETHYL CHLOROSILANE

The infrared (3200-50 cm(-1)) and Raman (3200-10 cm(-1)) spectra of ga seous and solid ethyl chlorosilane (CH3CH2SiH2Cl) have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and q ualitative depolarization values have been obtained. Both the gauche a nd trans conformers have been identified in the vibrational spectra of the fluid phases, but only the gauche conformer remains in the solid. Rom the far infrared spectrum of the gas, the fundamental torsion for the gauche conformer has been observed at 79.1 cm(-1). A variable tem perature study of the Raman spectrum of the liquid was carried out and the enthalpy difference was found to be 204 +/- 23 cm(-1) (583 +/- 66 cal mol(-1)), with the gauche conformer being the more stable form. A complete vibrational assignment is proposed based on infrared band co ntours, depolarization ratios, and group frequencies. The assignment i s supported by ab initio calculations using the RHF/3-21G basis set t o obtain the force constants and potential energy distribution. It is shown that the earlier reported r(0) carbon-hydrogen distances were in error and revised r(0) structural parameters are proposed. Additional ly, ab initio calculations have been carried out utilizing the RHF/3-2 1G, RHF/6-31G* and/or MP2/6-31G* basis sets, from which the conformat ional stability, barrier to internal rotation, and optimized structura l parameters have been obtained. The results of this study are compare d to corresponding results of some related molecules.