Laser Raman spectra and free and restricted rotation in phenyl silicates

Abstract

Tetraphenyl silicate and related phenyl-alkyl silicates, an interesting class of compounds with applications in high vacuum technology, belong to the class of non-rigid molecules where free or restricted internal rotation of the substituent phenyl and alkyl groups provide several possible relative orientations. This may result in the formation of different phases under different conditions, providing results of fundamental interest in molecular dynamics. We have recently studied the laser Raman and infrared spectra of some of these compounds including tetraphenyl, phenyl triphenoxy, alkyl triphenyl, diphenyl dialkyl, phenyl trialkyl, and tetra alkyl silicates. Changes are observed in the spectra of these molecules with temperature, and these indicate the onset of restricted rotation at lower temperatures. These spectral changes and assignments are discussed in the paper.