Resonant photoionization cross sections and branching ratios for atomic oxygen

Abstract

Total and partial photoionization cross sections for the ejection of either a $2p$ or a $2s$ electron from the ground ${2s}^{2}{2p}^{4}{}^{3}P$ state of atomic oxygen have been investigated using the R-matrix method. Cross sections are dominated by Rydberg series of autoionizing resonances converging to several ionic states. The autoionizing states are analyzed and identified using a procedure of eigenphase gradients. Comparison of our results with available previous calculations and experiments is shown to lead to some interesting conclusions regarding the importance of electron correlation and normalization of the measured relative cross sections. Our calculation removed long-standing discrepancy between theory and experiment regarding the shape of photoionization cross section near the ${}^{2}{P}^{o}$ threshold. The calculated branching ratios for the production of ${}^{4}{S}^{o},{}^{2}{D}^{o},$ and ${}^{2}{P}^{o}$ states at 584 and $304 \mathrm{\AA{}}\mathrm{}$ show good agreement with experiments.