State to state study of the dissociation of doubly charged carbon dioxide cations

Abstract

Double photoionization of CO2 has been studied in the photon energy range 37–52 eV by the photoion–photoion coincidence (PIPICO) method. Three dissociative electronic states (α̃, β̃, and γ̃) of CO++2 have been observed with threshold energies at, respectively, 37.9, 40.5, and 45.0 eV. Comparison of these energies with those recently calculated by Flament et al. indicates that the lowest electronic state at 37.9 eV most probably corresponds to the 1∑+g state (1π−2g main configuration). CO++2 in its α̃, β̃, and γ̃ states dissociates into CO++O+ with a high exothermicity since the total kinetic energy released was found to be respectively 4.5, 6.5, and 9.4 eV. From these results we concluded that CO++2 in its α̃(1∑+g ) state dissociates into CO+(X 2∑+)+O+(4Su) via an indirect process (predissociation). Absolute values of the partial double photoionization cross sections σ++n (E) (n≡α̃, β̃, and γ̃) were also determined as a function of the photon excitation energy E. A ratio of double to total photoionization cross sections as high as 3% at a 52 eV photon energy was observed.