The dissociative electroionization of carbon dioxide by low-energy electron impact. The C + , O + and CO + dissociation channels

This work reports the dissociative ionization of CO 2 between 19 and 40 eV. The three dissociation channels producing C +, O + and CO + are examined in detail. Translational energy distributions as a function of the impinging electron energy and the ionization efficiency for fixed minimum kinetic energy carried by the fragments are measured. The kinetic energy versus appearance energy diagram is obtained for the three fragment ions. When available, the present results are compared with previous measurements. The lowest appearance energy of O + and CO + corresponds to the predissociation of the CO 2 + (C 2 Σ g + ) state. At higher energies, all the fragment ions are exclusively produced by the dissociative ionization of CO 2 in the multiple electron transition (MET) states. Predissociation is most probably the dominant mechanism. Each MET state branches off to produce not only the three fragments, but also the same fragment in two different states. This is observed for each dissociation channel, i.e. O +, CO + and/or C +. In the latter channel no evidence is found for the dissociative ionization reaction CO 2 + → C + + 2 O.