Anion–aromatic molecule complex. Ab initio study of the benzene⋅O2 anion

A series of ab initio calculations were carried out for the O2⋅benzene complex and its anions to determine their structures and the O2⋅benzene adiabatic electron affinity. The calculations revealed interesting differences between the electronic and molecular structures of the anion and the neutral complex, and between the free and complexed O2−. While for O2⋅benzene the calculations predict two equilibrium structures, one planar and one with O2 located above the benzene and interacting with its π electrons, for [O2⋅benzene]− only the planar structure was predicted to be stable. Analysis of the [O2⋅benzene]− wave function shows some delocalization of the excess electron from O2− to the region of the σ electrons in benzene. This delocalization may explain the predicted increase of the adiabatic electron affinity (A.E.A) by 0.59 eV upon O2 complexation with benzene. This increase is consistent with A.E.A. shift reported in the accompanying paper by Le Barbu et al. [J. Chem. Phys. 116, 9663 (2002)].