Photoionization of tungsten ions: experiment and theory for W${}^{4+}$

Abstract

Experimental and theoretical results are reported for single-photon single ionization of the tungsten ion W${}^{4+}$. 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 W${}^{4+}$. Calculations were carried out for the $4f^{14}5s^{2}5p^{6}5d^2{}^3{\mathrm{F}}_J$, $J$=2, ground level and the associated fine-structure levels with $J$=3 and 4 for the W${}^{4+}$ ions. In addition, cross sections have been calculated for the metastable levels $4f^{14}5s^{2}5p^{6}5d^2{}^3{\mathrm{P}}_{0,1,2},{}^1{\mathrm{D}}_2,{}^1{\mathrm{G}}_4,{}^1{\mathrm{S}}_0$. Very satisfying agreement of theory and experiment is found for the photoionization cross section of W${}^{4+}$ which is remarkable given the complexity of the electronic structure of tungsten ions in low charge states.

15 pages, 3 figures, to appear in the Journal of Physics B: Atomic, Molecular and Optical Physics