SPECTRA AND STRUCTURE OF SILICON-CONTAINING COMPOUNDS .17. VIBRATIONAL AND MICROWAVE-SPECTRA, MOLECULAR-STRUCTURE, BARRIER TO INTERNAL-ROTATION AND AB-INITIO CALCULATIONS OF METHYLTRICHLOROSILANE

The vibrational spectra of gaseous, liquid and solid CH3SiCl3 and CD3S iCl3 have been recorded from 3500 to 40 cm-1. The fundamental vibratio ns have been assigned, and the degree of vibrational coupling among th e normal modes has been determined. A normal coordinate analysis has b een carried out by using the force constants obtained from ab initio c alculations with the 3-21G basis set. The microwave spectrum of CD3Si Cl3 has been recorded from 26.5 to 40.0 GHz and the A rotational const ants of seven isotopomers in a weighted least-squares procedure are: r (Si-C) = 1.841 +/- 0.005 angstrom, r(Si-Cl) = 2.030 +/- 0.001 angstrom , less than with left parenthesis through ClSiC = 110.5 +/- 0.1-degree s, less than with left parenthesis through ClSiCl = 108.4 +/- 0.2-degr ees, less than with left parenthesis through HCSi = 109.7 +/- 0.1-degr ees and less than with left parenthesis through HCH = 109.3 +/-0.1-deg rees. The barrier to internal rotation has been estimated from the rel ative intensity of the torsional satellites in the microwave spectrum to be 2.3 and 2.6 kcal/mol, for the -d0 and -d3 molecules, respectivel y, and from direct observation of the two-quantum transitions in the R aman effect, to be approximately 2.5 kcal/mol for both isotopomers. Th e structural parameters, barrier to internal rotation, and fundamental vibrational frequencies which have been determined experimentally are compared to those obtained from ab initio calculations employing the RHF/3-21G and/or RHF/6-31G* basis sets. Additionally, structural para meters have been calculated with the 6-31G basis set with electron co rrelation at the MP2 level. All of the results are discussed and compa red to the corresponding quantities obtained for some similar molecule s.