The vibrational spectra of CO2+, (CO2)2+, CO2−, and (CO2)2− trapped in solid neon

When a Ne:CO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned to CO2+, (CO2)2+, CO2−, and (CO2)2−. The lowest (μ 2∑u+) Renner component of the bending fundamental of CO2+ trapped in a neon matrix appears near the gas-phase band center, but other Renner components are undetectable. Absorptions of a photolabile product correspond to the recently identified CO-stretching fundamentals of (CO2)2+. Weak infrared absorptions at 1253.8 and 714.2 cm−1 are assigned to ν1 and ν2 of CO2−, respectively, and a moderately intense absorption at 2894.7 cm−1 is assigned to the ν1+ν3 combination band of that product. As in other recent argon- and neon-matrix studies, two weak infrared absorptions can be assigned to the two infrared-active OCO-stretching fundamentals of the D2d structure of (CO2)2−. Detailed isotopic substitution studies support all of these assignments. A weak absorption near the CO2 bending fundamental, for which isotopic substitution data are incomplete, may be contributed either by a second fundamental of (CO2)2− (D2d) with b2 symmetry or by a weakly interacting (CO2)n⋅⋅CO2− complex. Such ion–molecule complexes contribute other absorptions near ν3 of CO2 and of CO2−.