Spectra and structure of silicon-containing compounds.: Part XXXVIII: Infrared and Raman spectra, vibrational assignment, conformational stability, and ab initio calculations of vinyldifluorosilane

Abstract

Infrared spectra (3500–50 cm−1) of gaseous and solid, and Raman spectrum (3500–30 cm−1) of liquid vinyldifluorosilane, CH2CHSiF2H, are reported. Both the cis and gauche rotamers have been identified in the fluid phases. From temperature-dependent FT-infrared spectra of krypton solutions, it is shown that the cis conformer is more stable than the gauche form by 119±12 cm−1 (1.42±0.14 kJ mol−1). At ambient temperature there is 53±2% of the gauche conformer present. Complete vibrational assignments are provided for the cis conformer and several modes are identified for the gauche form. Harmonic force constants, fundamental frequencies, infrared intensities, and Raman activities have been obtained from MP2/6-31G(d) calculations with full electron correlation. The optimized geometries and conformational stabilities have also been obtained from ab initio MP2/6-31G(d), MP2/6-311+G(d,p), and MP2/6-311+G(2d,2p) calculations with full electron correlation as well as from density functional theory calculations (DFT) by the B3LYP method. The SiH bond distances (r0) of 1.472 and 1.471 Å have been obtained for the cis and gauche conformers, respectively, from the silicon–hydrogen stretching frequencies. These results are compared to the corresponding quantities of the corresponding carbon analogue as well as with some similar molecules.