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Experimental and theoretical cross sections are reported for single-photon single ionization of W5+ ions. Absolute measurements were conducted employing the photon-ion merged-beams technique. Detailed photon-energy scans were performed at (67 ± 10) meV resolution in the 20-160 eV range. In contrast to photoionization of tungsten ions in lower charge states, the cross section is dominated by narrow, densely-spaced resonances. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach employing a basis set of 457 levels providing cross sections for photoionization of W5+ ions in the ground level as well as the and metastable excited levels. Considering the complexity of the electronic structure of tungsten ions in low charge states, the agreement between theory and experiment is satisfactory.

Measurements of the single-photoionization cross-section of Cu-like Zn+ ions are reported in the energy (wavelength) range 17.5 eV (708 Å) to 90 eV (138 Å). The measurements on this trans-Fe element were performed at the Advanced Light Source synchrotron radiation facility in Berkeley, California at a photon energy resolution of 17 meV using the photon-ion merged-beams end-station. Below 30 eV, the spectrum is dominated by excitation autoionizing resonance states. The experimental results are compared with large-scale photoionization cross-section calculations performed using a Dirac Coulomb R-matrix approximation. Comparisons are made with previous experimental studies, resonance states are identified and contributions from metastable states of Zn+ are determined.

Experimental and theoretical results are reported for single-photon single ionization of the tungsten ion W4+. Absolute cross sections have been measured employing the photon-ion merged-beams setup at the Advanced Light Source in Berkeley. Detailed photon-energy scans were performed at 200 meV bandwidth in the 40-105 eV range. Theoretical results have been obtained from a Dirac-Coulomb R-matrix approach employing basis sets of 730 levels for the photoionization of W4+. Calculations were carried out for the 4f14 5s2 5p6 5d23FJ, J = 2, ground level and the associated fine-structure levels with J = 3 and 4 for the W4+ ions. In addition, cross sections have been calculated for the metastable levels 4f14 5s2 5p6 5d23P0,1,2, 1D2, 1G4, 1S0. A very satisfying agreement of theory and experiment is found for the photoionization cross section of W4+ which is remarkable given the complexity of the electronic structure of tungsten ions in low charge states.

Experimental and theoretical results are reported for single-photon single ionization of W2+ and W3+ tungsten ions. Experiments were performed at the photon-ion merged-beam setup of the Advanced Light Source in Berkeley. Absolute cross sections and detailed energy scans were measured over an energy range 20-90 eV at a bandwidth of 100 meV. Broad peak features with widths typically around 5 eV have been observed with almost no narrow resonances present in the investigated energy range. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach. The calculations were carried out for the lowest-energy terms of the investigated tungsten ions with levels 5s 5p 5d DJ = for W2+ and 5s 5p 5d FJ= for W3+. Assuming a statistically weighted distribution of ions in the initial ground-term levels there is good agreement of theory and experiment for W3+ ions. However, for W2+ ions at higher energies there is a factor of approximately two difference between experimental and theoretical cross sections.

Experimental and theoretical results are reported for photoionization of Ta-like (W+) tungsten ions. Absolute cross sections were measured in the energy range 16-245 eV employing the photon-ion merged-beam setup at the advanced light source in Berkeley. Detailed photon-energy scans at 100 meV bandwidth were performed in the 16-108 eV range. In addition, the cross section was scanned at 50 meV resolution in regions where fine resonance structures could be observed. Theoretical results were obtained from a Dirac-Coulomb R-matrix approach. Photoionization cross section calculations were performed for singly ionized atomic tungsten ions in their J = 1/2, ground level and the associated excited metastable levels with J = 3/2, 5/2, 7/2 and 9/2. Since the ion beams used in the experiments must be expected to contain long-lived excited states also from excited configurations, additional cross-section calculations were performed for the second-lowest term, J = 5/2, and for the 4F term, with J = 3/2, 5/2, 7/2 and 9/2. Given the complexity of the electronic structure of W+ the calculations reproduce the main features of the experimental cross section quite well.

Absolute single-photoionization cross-section measurements for Se2+ ions were performed at the Advanced Light Source at Lawrence Berkeley National Laboratory using the merged-beams photo-ion technique. Measurements were made at a photon energy resolution of 24±3 meV in the photon energy range 23.5-42.5 eV, spanning the ground state and low-lying metastable state ionization thresholds. To clearly resolve the resonant structure near the ground-state threshold, high-resolution measurements were made from 30.0 to 31.9 eV at a photon energy resolution of 6.7±0.7 meV. Numerous resonance features observed in the experimental spectra are assigned and their energies and quantum defects tabulated. The high-resolution cross-section measurements are compared with large-scale, state-of-the-art theoretical cross-section calculations obtained from the Dirac Coulomb R-matrix method. Suitable agreement is obtained over the entire photon energy range investigated. These results are an experimental determination of the absolute photoionization cross section of doubly ionized selenium and include a detailed analysis of the photoionization resonance spectrum of this ion.