Theoretical studies of cross sections and photoelectron angular distributions in the valence photoionization of molecular oxygen

Abstract

Photoionization from ground state of molecular oxygen leading to a number of 1πg−1, 1πu−1, 3σg−1, and 2σu−1 ion states have been investigated for photon energies up to 50 eV using the multichannel Schwinger method with configuration interaction. The use of a multichannel approach and correlated targets not only enables us to obtain results in good agreement with experimental data, but also leads to a better understanding of electron correlation effects in these photoionization processes. In addition to numerous Rydberg-type autoionization states that have been identified in the multichannel study, substantial effects of the open-channel coupling have also been found in almost every channel. These effects are evidences of the strong electron correlation in the photoionization dynamics of this system. The most significant interchannel coupling effect exists in the photoionization to the 3σg−1 channels, in which a complete failure of the single-channel photoionization description is found in the shape resonance process. In contrast to earlier theoretical studies, we found only one shape resonance in the photoionization to the 3σg−1 channels instead of two separated multiplet-specific shape resonances. A full description of the resonant state requires the inclusion of coupling to other valence photoionization channels. The photoelectron angular distributions have also been computed and compared to the existing experimental data. Good agreement between experiment and theory has been achieved. In this study, we also calculated molecular orientation parameters under the fixed-nuclei approximation, which contain symmetry information about the resonances and outgoing waves and which can be used to characterize the dynamics of the photoionization.