The unusual behavior of the A 2Πu state of the O2− ion

Abstract

The inner wall of a recently calculated potential energy curve of the A 2Πu state of the O2− ion shows a curious falttening. To explain and correct this, various aspects of the model used for the MCSCF calculations are analyzed. The interesting finding is that for the adiabatic potential curve the flattening is real and at distances <2.5 bohrs, a Rydberg-like 2Πu state has a lower energy than the lowest valence 2Πu state. This leads to a distortion of the repulsive wall of the adiabatic A 2Πu state and also to a potential well in the complementary adiabatic B 2Πu state (which is valence in character at short distances and Rydberg-like at large distances). Implications of this avoided crossing for electron scattering from O2 are discussed.