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 dist ribution 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+ ion s in the a (4)Pi(u) State with a lifetime of more than 30 mu sec and that c ollision induces curve-crossing between the (4)Pi(u) and (4)Sigma(g)(-) sta tes of CO2+. The process becomes endothermic at low electron energy, suppor ting the above conclusion. (C) 1999 Elsevier Science B.V. All rights reserv ed.