Stability properties of CO22+

The carbon dioxide molecular dication is investigated by multireference configuration interaction computations. Whereas the system is found to be unbound by D_e = —5.12 eV with respect to fragmentation into CO⁺(²Š⁺) + O⁺(⁴S_u), the ground-state potential energy surface of CO²⁺₂ enjoys a local minimum for a collinear symmetric configuration where the carbon nucleus is centred between the outer two oxygen nuclei (with internuclear separation R_C-O = 1.22 Å). Potential barriers larger than 1 eV render the corresponding electronic ground state ³Š^g_- metastable against dissociative tunnelling. For the lowest seven excited states and system configurations restricted to linear symmetric geometries, potential energy curves are presented and compared with the experimental double ionization spectrum of CO₂ in the Franck-Condon region.