Ab initio study of the molecular structure and potential energy surface of disiloxane

Abstract

The molecular structure of disiloxane, SiH 3OSiH 3, has been investigated in quantum-mechanical ab initio calculations at the SCF and CPF levels. The energy of disiloxane was calculated as a function of coordinates of the three large-amplitude motions: the SiOSi bending and internal rotations of the silyl groups. The geometrical parameters were optimized at both SCF and CPF levels; the optimum geometries were determined for several values of coordinates of the large-amplitude motions. The harmonic force field and frequencies of small-amplitude vibrations were calculated at the SCF level as functions of coordinates of the large-amplitude motions. As a result, the equilibrium and effective, including some effects of the small-amplitude vibrations, potential energy surfaces of the large-amplitude motions were determined. At the SCF level, the SiOSi skeleton was found to have a linear equilibrium geometry. At the CPF level, the SiOSi skeleton was found to be bent at equilibrium; the calculated equilibrium SiOSi angle is 152° and the barrier to linearity of the SiOSi skeleton is 83 cm −1, both values being in good agreement with experimental data and consistent with the quasi-symmetric top model of the disiloxane molecule.