Infrared spectra of HOCO+ and of the complex of H2 with CO2- trapped in solid neon

When a Ne:H-2:CO2=800:10:1 mixture is codeposited at 4.3 K with neon atoms that have been excited in a microwave discharge, the infrared spectrum of the resulting solid deposit includes not only absorptions characteristic of experiments from which H-2 is absent, but also numerous product absorptions that are common to similar experiments on Ne:HCOOH samples. The carriers of these latter absorptions include HCOOH itself, as well as trans-HOCO, HCOOH+, and HCO2-. Detailed isotopic substitution studies confirm the infrared identifications of HCOOH+ and HCO2- and permit the identification of two previously unassigned vibrational fundamentals each of HOCO+ and DOCO+. Density functional calculations for the latter species support the proposed assignments. Evidence is presented for the stabilization of the H-2...CO2- anion complex, in which the H-2 moiety becomes infrared-active. The processes that result in the stabilization of these products are considered.