INFRARED STUDY OF LOW-TEMPERATURE ADSORPTION .1. CO ON AEROSIL - INTERPRETATION OF THE HYDRATED SILICA SPECTRUM

IR spectra of CO physically adsorbed on Aerosil were recorded at 123 K. Spectral modifications have been examined as a function of coverage and surface hydroxylation in the region 4000-700 cm-1. Computer simulation of IR spectra in the CO stretching region was performed. The free silanols act as interaction centers via a weak hydrogen bond, as clearly shown by the perturbation of OH stretching and bending modes. We interpret that on highly dehydroxylated samples the interacting silanols are isolated, whereas on highly hydroxylated samples the majority are present as free partners in couples of silanols, H bonded with different strengths. On the dehydrated part of the surface interaction arises via dispersion forces; two different sites for such interaction are present on highly dehydrated samples. Reactivity of the acidic Lewis sites is also observed. In all cases the degrees of freedom of the adsorbed molecules seem to be restricted to libration only. © 1979 American Chemical Society.