SPECTRA AND STRUCTURES OF SILICON-CONTAINING COMPOUNDS - XXIV - RAMANAND INFRARED-SPECTRA, R(0) STRUCTURAL PARAMETERS, VIBRATIONAL ASSIGNMENT, BARRIERS TO INTERNAL-ROTATION, AND AB-INITIO CALCULATIONS OF ETHYLSILANE

The infrared (3200 to 400 cm(-1)) and Raman (3200 to 20 cm(-1)) spectr a of gaseous and solid ethylsilane, CH3CH2SiH3, have been recorded. Ad ditionally, the Raman spectrum of the liquid has been obtained with qu antitative depolarization values. The SIH, torsional mode has been obs erved as sum and difference bands with the silicon-hydrogen stretching vibration. Utilizing the torsional fundamental frequency of 132 cm(-1 ) the threefold periodic barrier of 590 cm(-1) (7.06 kJ/mol) has been obtained. Utilizing the frequencies of the silicon-hydrogen stretches, Si-H bond distances of 1.485 and 1.484 Angstrom have been obtained fo r the bonds gauche and trans to the methyl group, respectively. Using previously reported rotational constants from seven different isotopom ers, the r(0) parameters have been calculated and are compared to the corresponding r(s) parameters. A complete vibrational assignment is pr oposed that is consistent with the predicted frequencies utilizing the force constants from ab initio MP2/6-31G(d) calculations. Both the in frared intensities as well as the Raman activities and depolarization values have been obtained from the ab initio calculations. Complete eq uilibrium geometries have been determined by ab initio calculations em ploying the 6-31G(d), 6-311+G(d,p), and 6-311+G(2d,2p) basis sets at l evels of restricted Hartree-Fock (RHF) and/or Moller-Plesset (MP) to s econd order. The results are discussed and the theoretical values are compared to the experimental Values when appropriate.