The change in spectrum of surface hydroxyl groups and in the spectra of benzene, toluene, p-xylene and mesityfene molecules during adsorption on aerosils of various degrees of dehydroxylation has been studied. It was observed that mainly the free hydroxyl groups of the silica surface participate in the adsorption interaction. The shift of the absorption band of the free hydroxyl groups depends on the structure of the adsorbed molecuIe and on the surface coverage. There exists a relation between the magnitude of this shift and the heat of adsorption. It is established that the degree of hydroxylation and the surface coverage influence the location and intensity of the bands of the out-of-plane CH deformation of the benzene molecule. The changes in the spectrum during adsorption are due to the interaction between the n-electron system of the aromatic molecules and the hydroxyl groups of the silica surface.

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