VIBRATIONAL ANALYSIS OF SI(OC2H5)(4) AND SPECTROSCOPIC STUDIES ON THEFORMATION OF GLASSES VIA SILICA-GELS

Theoretical and experimental band assignments for the infrared (IR) an d Raman spectra of Si(OC2H5)(4) (tetraethoxysilane: TEOS) have been ma de based on the structure of -SiO4- (T-d), -Si(OC)(4)- (S-4) and -OC2H 5 (C-s) fragments. The few bands observed in both the IR and Raman spe ctra of TEOS led to the assumption of a high symmetry for this compoun d. To verify the experimental assignments of the frequencies a normal coordinate analysis was performed. The calculated force constants for the Si-O, C-O, C-C and C-H bonds agree well with previous results foun d in the literature. Also MNDO-91 calculations were carried out to obt ain the geometrical parameters of Si(OC2H5)(4). TEOS was used to produ ce gels through an acid-catalyzed hydrolysis. These gels were subseque ntly heated at different temperatures in order to transform them into glasses. Infrared measurements were carried out to monitor the changes in the IR spectra as the gels evolved to glasses.