A note on the electronic structure of O 2 ?

The electronic spectrum of O2− is reinvestigated using CASSCF and CI methods. In particular, a previously noted curious flattening of theA2Πu curve has been studied in detail. The present analysis disagrees with the previous one where this flattening was found to be a result of an avoided curve crossing between a valence and a Rydberg state of O2−. A simple procedure is suggested to determine whether a wavefunction is of real Rydberg character or if the bound character of the state is just an artefact of the calculation.