Infra-red spectra of CO2 adsorbed on evaporated alkali halides

Abstract

The infra-red spectrum of CO₂ adsorbed on high-surface-area films of evaporated alkali halides has been investigated at different temperatures and surface coverages. The ν₃ vibration has been obtained as a sharp, strong, single band. For NaCl and NaI films, the ν₂ vibration always appeared as a well-resolved doublet. Possible reasons for the appearance of the doublet are discussed, the most acceptable being the removal of degeneracy in the adsorbed state. For CsCl and CsI, the ν₂ doublet appeared at higher surface coverages only. The possible relation between the spectrum observed and the crystalline structure of the substrate is discussed. From the shape and temperature independence of ν₂ and ν₃ absorption bands it is concluded that, in the system studied, no rotation exists in the adsorbed state.