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

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-outʹ mechanism. We propose that 70 eV electron ionization produces a significant fraction of CO2+ ions in the a 4Πu state with a lifetime of more than 30 μsec and that collision induces curve-crossing between the 4Πu and 4Σ−g states of CO2+. The process becomes endothermic at low electron energy, supporting the above conclusion.