Vibrational spectra of hexafluorodisiloxane and internal rotation around the SiO bond. An ab initio study

Abstract

The structure of hexafluorodisiloxane was optimized at different levels of theory up to MP2/6-31G ∗, and the vibrational spectrum was calculated and compared with the experimental one. It was shown that at the Hartree-Fock level the simple SCF/3–21 (O ∗) basis set gives satisfactory results. The geometry was also optimized at two C 2 v structures which appear to be saddle points on the SiF 3 rotor potential curve. The significant change of the SiOSi angle equilibrium value in the course of the SiF 3 group rotation was explained by assuming repulsion between lone pair electrons of fluorines and oxygen. This effect is also revealed in the predicted change in the ν as SiOSi frequency on going from the C 2 to the C 2 v structure. This provides the explanation of some unusual features in the vibrational spectra of hexahalodisiloxanes, namely large gas-solid shifts of ν as SiOSi and splitting of this mode in the matrices.