Ion-pair states of O2

Valence states of O2 that correlate adiabatically to the ion pair asymptote, O+(4S)+O−(2P), have been calculated using the multiconfiguration description of the electronic structure. The production of the ion pair is attributed to valence–Rydberg mixing that predissociates Rydberg states of the excited O2+ ion such as those leading to the b 4Σ−g state. The electronic states required the calculation of excited states of a given symmetry. This is possible with the BISON-MC codes if the rigorous restriction on orthogonality to the lower states is relaxed. For homonuclear valence states, in particular, this should be a good approximation.