Photoionization cross sections and oscillator strengths for oxygen ions: O I-O VII

Abstract

Ab initio close-coupling calculations are reported using the R-matrix method for photoionization cross sections $({\ensuremath{\sigma}}_{\mathrm{PI}}),$ oscillator strengths (f values), and energy levels (E) for oxygen ions: O I, O II, O III, O IV, O V, O VI, and O VII. Total, partial, and state-specific photoionization cross sections are computed and investigated in detail. Important features are found that should affect overall photoionization and recombination, especially at high temperatures and energies. Although these ions have been previously studied individually, present work aims at studying them as an isonuclear sequence and obtaining more accurate and complete results for applications. More extended eigenfunction expansions than in previous works, including $n=3$ states, show correlation effects primarily manifested as additional groups of resonances in photoionization of oxygen ions such as O VI and O VII that are of importance in extreme ultraviolet and x-ray laboratory and astrophysical plasmas. Lifetimes of excited bound states are obtained from the present oscillator strengths and compared with experiments. The computed radiative atomic parameters, energy levels, oscillator strengths, and photoionization cross sections constitute a larger dataset than the Opacity Project data [M. J. Seaton, J. Phys. B 20, 6363 (1987)], with which comparisons are made.