Collision-induced dissociation of CO2+ cations: evidence for a long-lived excited state

Abstract

Collision-induced dissociation of CO₂⁺ ions formed by 70 eV electrons [CO₂⁺ Ar, CO+Ar)O⁺ ] at 49 eV is translationally exothermic. The intensity distribution of O⁺ is symmetric about the Ar/O⁺ center-of-mass rather than that for Ar/CO₂⁺, consistent with a spectator `knock-out' mechanism. We propose that 70 eV electron ionization produces a significant fraction of CO₂⁺ ions in the a ⁴Π_u state with a lifetime of more than 30 μsec and that collision induces curve-crossing between the ⁴Π_u and ⁴Σ_g^- states of CO₂⁺. The process becomes endothermic at low electron energy, supporting the above conclusion.