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Absolute cross-section measurements for valence-shell photoionization of Ar + ions are reported for photon energies ranging from 27.4 to 60.0 eV. The data, taken by merging beams of ions and synchrotron radiation at a photon energy resolution of 10 meV, indicate that the primary ion beam was a statistically weighted mixture of the 2 P o 3/2 ground state and the 2 P o 1/2 metastable state of Ar + . Photoionization of this Cl-like ion is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. Observed resonance line shapes indicate interference between indirect and direct photoionization channels. Resonance features are spectroscopically assigned and their energies and quantum defects are tabulated. The measurements are satisfactorily reproduced by theoretical calculations based on an intermediate coupling semirelativistic Breit-Pauli approximation.

High-resolution absolute experimental measurements and two independent theoretical calculations were performed for photoionization of O 1 ions from the 2 P o and 2 D o metastable levels and from the 4 S 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.

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Using the merged-beams technique, O+ photofragment yield spectra from photofragmentation of CO+ were measured at photon energies ranging from 20.5 to 34.5 eV. Resonant structures are identified as members of Rydberg series belonging to electronic core excited states of the C+ + O+ fragmentation channel. Additional structures originating from initial vibrational excitations of the CO+ beam have also been identified. Lower-bound values for the CO+ photofragmentation cross sections are estimated based on trajectory simulations for the apparatus and on known photofragment angular distributions.