Probing the quantal identity of low-lying electronic states ofCO2+by quantum-chemical calculations and ion-translational-energy spectrometry

Potential-energy curves of various electronic states of ${\mathrm{CO}}^{2+}$ and ${\mathrm{CO}}^{+}$ are computed using all-electron ab initio molecular-orbital methods. Configuration-interaction effects are treated by perturbative techniques (using Möller-Plesset perturbation theory to fourth order) and by variational methods (using the coupled-cluster approach). In the case of ${\mathrm{CO}}^{2+}$, calculations indicate that the lowest-energy ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }$ and ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ states are nearly degenerate in the Franck-Condon region but that only the latter is likely to be metastable; the former is expected to predissociate rapidly due to a curve crossing with a purely repulsive ${}_{}{}^3{}_{}{}^{}\mathrm{\Sigma }_{}^{\mathrm{-}}{}_{}{}^{}$ state. Experimental measurements have been carried out on the kinetic energy released when metastable ${\mathrm{CO}}^{2+}$ ions dissociate by a tunneling mechanism, using an ion-translational-energy spectrometer. The kinetic-energy spectra are measured of fragment ions produced when ${\mathrm{CO}}^{2+}$ dissociates via an intermediate highly excited (dissociative) ${\mathrm{CO}}^{+\mathrm{*}}$ state populated in an electron-capture reaction in collision with He. The experimental results remain difficult to interpret within the framework of the computed potential-energy curves.