Photoionization of Metastable $O^{+}$ Ions: Experiment and Theory

High-resolution absolute experimental measurements and two independent theoretical calculations were performed for photoionization of ${\mathrm{O}}^{+}$ ions from the ${}_{}{}^2{}_{}{}^{}P_{}^{\mathrm{o}}{}_{}{}^{}$ and ${}_{}{}^2{}_{}{}^{}D_{}^{\mathrm{o}}{}_{}{}^{}$ metastable levels and from the ${}_{}{}^4{}_{}{}^{}S_{}^{\mathrm{o}}{}_{}{}^{}$ ground state in the photon energy range 30–35.5 eV. This is believed to be the first comparison of experiment and theory to be reported for photoionization from metastable states of ions. While there is correspondence between the predicted and measured positions and relative strengths of the resonances, the cross-section magnitudes and fine structure are sensitive to the choice of basis states.