Photoionization of the Mg-like S4+ Ion in Ground and Metastable States: Experiment and Theory

We report calculations and measurements of the absolute photoionization cross section of the magnesium-like S4+ ion over the 160-270 eV photon energy range. The experiments were performed with the merged photon-ion MAIA apparatus at the Soleil synchrotron radiation facility. Single and double ionization ion yields produced by the photoionization of the 2p subshell of the S4+ ion both from the 2p63s2 1S0 ground state and the 2p53s3p(3P0,2) metastable levels were observed, as well as 2s excitations. Calculations of the photoionization cross sections were carried out using Multi-Configuration Dirac-Fock and R-matrix codes and the results are compared with the experimental data.