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Photoionization of the $3s^23p^4~ ^3P$ and the $3s^23p^4~^1D,~^1S$ states of sulfur: experiment and theory

Photoionization of neutral atomic sulfur in the ground and metastable states was studied experimentally at a photon energy resolution of 44 meV FWHM. Relative cross section measurements were recorded by using tunable vacuum ultraviolet (VUV) radiation in the energy range 9 -- 30 eV obtained from a laser-produced plasma and the atomic species were generated by photolysis of molecular precursors. Photoionization of this atom is characterized by multiple Rydberg series of autoionizing resonances superimposed on a direct photoionization continuum. A wealth of resonance features observed in the experimental spectra are spectroscopically assigned and their energies and quantum defects tabulated. The cross-section measurements are compared with state-of-the-art theoretical cross-section calculations obtained from the Dirac Coulomb R-matrix method. Resonances series in the spectra are identified and compared indicating similar features in both the theoretical and experimental spectra.