Photoionization dynamics of O2 and O3 for atmospheric and astrophysical applications

Abstract

The photoionization dynamics of molecular oxygen (O2) and ozone (O3) are investigated using the ab initio R-matrix method, incorporating explicit electron correlation and resonance effects. These two oxygen-bearing species are of fundamental importance in atmospheric photochemistry and astrophysical environments; however, quantitative data for their total and valence shell photoionization cross-sections remain incomplete. For O2, we computed the total and channel-resolved cross-sections associated with ionization from the 1πg, 1πu, and 3σg valence orbitals, leading to the X2Πg, a4Πu, A2Πu, b4Σg−, and B2Σg− ionic states, as well as additional Πu states (22Πu, 32Πu) that arise from mixed contributions, including ionization and excitation effects linked to their strong multiconfigurational character. The calculated cross-sections and their resonance structures show excellent agreement with available experimental measurements, accurately reproducing the near-threshold and autoionization features. For O3, high-resolution total and partial photoionization cross-sections corresponding to the 2A1(6a1−1), 2B2(4b2−1), and 2A2(1a2−1) ionic states are reported for the first time. The results reveal pronounced Rydberg series and resonance enhancements dominating the low-energy region, providing a comprehensive picture of the O3 photoionization continuum. The present benchmark dataset establishes a consistent framework for modeling O2 and O3 photoionization across atmospheric and astrophysical conditions and serves as a reference for future theoretical and experimental investigations.