CO adsorption at 77 K on KCl films. An infrared investigation

Abstract

KCl films have been prepared by vapour deposition in vacuo on a cold (77 K) NaCl plate and then sintered at room temperature for 12 h. The electron micrographs of the sintered film show that the crystallites have cubic shape and prevalently expose low-index {100} faces. The i.r. spectra of CO adsorbed at 77 K on both unsintered (high surface area) and sintered (low surface area) films can be interpreted in terms of CO species adsorbed on edges and steps and species adsorbed on flat portions of extended faces. The molecules adsorbed on the flat parts of {100} faces form a parallel array of oscillators localized at the cation sites, which are mutually interacting via dynamic and static mechanisms. The dynamic and static effects have been estimated by using isotopic ¹³CO–¹²CO mixtures. The dynamic polarizability of CO adsorbed on {100} faces has also been calculated.