The ab initio analysis of molecular geometry and force fields in H 3XOXH 3 (X = C, Si) series

Abstract

The GVFF of dimethyl ether, silyl methyl ether and disiloxane have been determined by the ab initio gradient method using 4-21G (for the first row elements) and 3-3-21G (for Si) basis sets augmented with d-functions on silicon and oxygen atoms. Equilibrium structures, obtained in the set which includes d-functions, indicate that methyl group CH bond length asymmetry decreases and silyl group asymmetry increases in silyl methyl ether. This is confirmed by the analysis of IR spectra. Methoxy and siloxy group scale factors for both basis sets were adjusted on experimental frequencies of dimethyl and silyl methyl ether isotopomers. The basis set without d-functions gives satisfactory description of these spectra. Siloxy group scale factors were transferred into the ab initio force field of disiloxane and the assignment, based on this field, is discussed.