MOLECULAR-STRUCTURE, FORCE-FIELD AND VIBRATIONAL-SPECTRA OF TETRAMETHOXYSILANE

IR and Raman spectra of Si(OCH3)4 and Si(OCD3)4 are reported and the peak assignments discussed. The equilibrium molecular geometry calculated by ab initio gradient methods agrees with the structure flattened along the S4 axis, established by an electron gas diffraction study. The initial force field model, a composite of the ab initio force fields of Si(OH)4 and H3SiOCH3 molecules, reproduces the experimental spectrum rather well, with the exception of the 1200-1000 cm-1 region. The addition of interaction force constants between non-adjacent SiO and CO stretching coordinates enables a fairly good description of vibrations in this frequency range to be made. Ab initio force constant calculations confirm the existence of these terms in the tetramethoxysilane force field.