Infra-red Studies of Reactions on Oxide Surfaces: Part 2.—Methanol on Silica

Abstract

Infra-red spectroscopy has been used to investigate the structure of the chemisorbed species which are formed when CH3OH, CH2DOH, CHD-OH and CD3OH react with silica. Force constant calculations utilizing only the CH and CD stretching modes have been used to show that the strongest spectral features can be assigned to an unsymmetrical surface SiOMe group which has one strong and two weak CH bonds. Some additional spectral features which reversibly grew in intensity with increasing sample temperatures have been assigned to a symmetrical SiOMe species which exists in equilibrium with unsymmetrical SiOMe. It has been suggested that the infra-red bands of sym metrical SiOMe are probably hot bands arising from transitions from the first vibrationally excited state of the SiOC bending mode such that rapid flipping of the SiOC bond can occur in this excited state.