Localized and delocalized 1s hole states of the O₂⁺ molecular ion

The hole states of O2+, obtained by ionization of the oxygen molecule, have been examined theoretically in three approximations: (i) The frozen orbital approximation, which consists of single configuration calculations in terms of the Hartree-Fock orbitals for the neutral O2 molecule; (ii) direct hole-state calculations in which g or a inversion symmetry is imposed on each molecular orbital; (iii) direct hole-state calculations without the restriction in (ii). For the 1s 4∑ - hole state the three approximations yield the following ionization potentials: (i) 563.5 eV; (ii) 554.4 eV; (iii) 542.0 eV. The experimental ionization potential is 543.1 eV, and it is concluded that the hole state is localized on one of the two oxygen atoms.