Vibrational spectra, r0 structural parameters, barriers to internal rotation, and ab initio calculations of ClCH 2SiH 3, Cl 2CHSiH 3, ClCH 2SiF 3 and Cl 2CHSiF 3

Abstract

The infrared (3200–400 cm −1) and Raman spectra (3500–40 cm −1) of gas/or liquid and solid chloromethylsilane, ClCH 2SiH 3, dichloromethylsilane, Cl 2CHSiH 3, chloromethyltrifluorosilane, ClCH 2SiF 3, and dichloromethyltrifluorosilane, Cl 2CHSiF 3, have been recorded and complete vibrational assignments are given for all four molecules. To support the spectroscopic study ab initio calculations by the Møller–Plesset perturbation method to second order MP2(full) and density functional theory calculations by the B3LYP method have been carried out. The Raman activities, infrared intensities vibrational frequencies and barriers to internal rotation have been predicted from MP2(full)/6-31G(d) calculations and these theoretical quantities are compared to the experimental ones when available. The r 0 Si–H distances for chloromethylsilane were determined to be 1.484 and 1.478 Å for the in-plane and out-of-plane atoms, respectively, from the Si–H stretching frequencies. The adjusted r 0 parameters for ClCH 2SiH 3 have been obtained by combining the ab initio MP2(full)/6-311+G(d,p) predicted values with the 12 previously reported microwave rotational constants. The heavy atom structural parameters for this molecule are: r 0(Si–C) = 1.886(3), r 0(Cl–C) = 1.791(3) Å with ∠ ClCSi of 109.3(5)°. Estimated r 0 parameters are given for the other three molecules. Barriers to internal rotation have been obtained from the torsional frequencies and the values are compared to the predicted values as well as the corresponding ones for the carbon analogues.