L -shell photoionization of Mg-like S4+ in ground and metastable states: Experiment and theory

Abstract

We report measurements of the absolute photoionization cross sections of magnesiumlike ${\mathrm{S}}^{4+}$ over the 158--280 eV photon energy range. The experiments were performed with the multianalysis ion apparatus at the SOLEIL synchrotron radiation facility. Single- and double-ionization ion yields produced by the photoionization of the $2p$ subshell of the ${\mathrm{S}}^{4+}$ both from the $2{p}^{6}3{s}^{2}{\phantom{\rule{0.16em}{0ex}}}^{1}{S}_{0}$ ground state and the $2{p}^{5}3s3p{\phantom{\rule{0.16em}{0ex}}}^{3}{P}_{0,1,2}$ metastable levels were observed, as well as $2s$ excitations. Theoretical calculations of the photoionization cross sections were carried out using multiconfiguration Dirac-Fock and $R$-matrix computer codes and the results are compared with the experimental data. While in general reasonably good agreement was found, notable differences in the strengths and positions of predicted resonances were observed and significant systematic energy shifts of the theoretical predictions were required.