Conformational stability, structural parameters, vibrational frequencies, and Raman and infrared intensities of allylsilane

The Raman spectra (3500 to 30 cm(-1)) of allylsilane, CH2CHCH2SiH3, in the liquid with quantitative depolarization ratios and solid states and the infrared spectra (3500 to 30 cm(-1)) of the gas and solid have been recorded. Similar data have also been recorded for the Si-d(3) isotopomer. Additionally, the mid-infrared spectra of the normal sample dissolved in liquified xenon as a function of temperature (-100 to -50 degrees C) have been recorded. All these data indicate there is a single conformer, the gauche rotamer, in all three physical states. Utilizing the Si-H stretching frequencies from the infrared spectrum of the gaseous CH2CHCH2SiD2H isotopomer, the three Si-H band distances (r(0)) are calculated to be 1.484 Angstrom for the gauche conformer. The other ro parameters are estimated from the previously reported rotational constants. The fundamental frequencies for the asymmetric (78 cm(-1)) and SiH3 (137 cm(-1)) torsions were obtained from sum and difference bands with the SiH3 stretches. From the SiH3 torsional frequency the barrier to internal rotation is calculated to have a value of 731 cm(-1) (8.74 kJ/mol). The optimized geometries, conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios, and vibrational frequencies have been obtained from RHF/6-31G* and/or MP2/6-31G* ab initio calculations. These quantities are compared to the corresponding experimental quantities when appropriate as well as with some corresponding results for some similar molecules.