Raman and infrared spectra, conformational stability, normal coordinate analysis, vibrational assignment and ab initio calculations of some silicon or germanium containing compounds

The infrared (3200 to 40 cm−1) spectra of gaseous, amorphous and annealed solids and Raman spectra (3200 to 20 cm−1 ) of liquid and/or solid have been recorded for a number of silicon or germanium containing organic compounds. Variable temperature (-55 to -150°C) studies of the mid-infrared spectra of the samples dissolved in liquid krypton and/or xenon have been recorded and the enthalpy differences determined for all compounds. The percentages of the conformers present at ambient temperature are estimated for all molecules. The geometrical parameters, harmonic force constants, vibrational frequencies, infrared intensities, Raman activities and depolarization ratios, and energy differences have been obtained for both the most stable and less stable conformers from ab initio MP2/6-31 G(d) calculations. Relatively complete vibrational assignments have been proposed for the most stable conformers and partial assignments for the less stable forms based on the predicted vibrational fundamental frequencies, relative infrared intensities, Raman activities, infrared band contours, and depolarization ratios. Structural parameters and energy differences have been obtained for all compounds by using ab initio calculations at the Hartree-Fock level and with full electron correlation by the perturbation method to second order with larger 6-311+G(d,p) and 6-311+G(2d,2p) basis sets with and without diffuse functions. Similar calculations by using density functional theory (DFT) by the B3LYP method have been carried out.;From the far infrared spectra of the gaseous samples torsional transition bands have been observed for some compounds. The potential functions governing the internal rotation with values of the constants have been determined for some molecules. By combining previously reported rotational constants with ab initio MP2/6-311+G(d,p) predicted parameters, adjusted r 0 parameters have been obtained for several compounds.