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

Theoretical and experimental band assignments for the infrared (IR) and Raman spectra of Si(OC2H5)(4) (tetraethoxysilane: TEOS) have been made based on the structure of -SiO4- (T-d), -Si(OC)(4)- (S-4) and -OC2H5 (C-s) fragments. The few bands observed in both the IR and Raman spectra of TEOS led to the assumption of a high symmetry for this compound. 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 found in the literature. Also MNDO-91 calculations were carried out to obtain the geometrical parameters of Si(OC2H5)(4). TEOS was used to produce gels through an acid-catalyzed hydrolysis. These gels were subsequently 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.