Lawrence Berkeley National Laboratory

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.