The infrared matrix isolation spectra of carbon dioxide. II. Argon matrices: the CO2 monomer bands

Evidence is presented that the cause of the doubling of the infrared bands of CO2 in an argon lattice is the presence of two types of acceptable sites for the CO2 molecule. The nature of these sites is discussed; it is concluded that the sites are double substitutional sites, in which a CO2 molecule occupies the place of two adjacent argon atoms, and single substitution sites, in which the CO2 molecule occupies the place of a single argon atom. A CO2 molecule in a double substitutional site is a more stable situation than a CO2 molecule in a single substitutional site: the former gives a higher v3 and lower v2 frequency than the latter.