Photoionization in Molecular Oxygen

Theoretical studies are reported of partial-channel photoionization cross sections in molecular oxygen employing the static exchange approximation and Stieltjes-Tchebycheff moment theory techniques. It is found to be particularly important in this prototypical open-shell case to specify the correct ionic parentages of the various multiplet photoionization states that arise in order to account for all the experimental features in the relatively complex photoelectron spectra, and to obtain corresponding partial-channel photoionization cross sections in good accord with measured values. Resonancelike structures in certain of the cross sections are attributed to contributions from diabatic valencelike states that appear in the appropriate photoionization continua, rather than in the corresponding discrete spectral intervals. These and other aspects of the photoionization spectrum in molecular oxygen are contrasted and compared with the results of previously reported studies in molecular nitrogen and carbon monoxide