Infra-red spectra of CO2 adsorbed on evaporated alkali halides
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.