Theoretical photoionization spectra for the ground state of a Mg-like Fe14+ ion converging to the Fe15+ 3l thresholds

The photoionization cross sections for the ground-state of a Mg-like Fe14+ ion converging to the Fe15+ 3l thresholds are calculated in LS coupling by using the variational eigenchannel R-matrix method, where is a much simpler technique than other extensive calculations such as the relativistic Breit-Pauli R-matrix method. The major approximation for this calculational formalism concerns the use of a Hamiltonian H that does not refer to the full atomic system, but represents only the valence electrons plus a central effective potential to represent the effects of the inner shell. The present calculational results are compared with the previous results obtained by considering the relativistic effects. With detailed descriptions for the resonances of the cross section across the Fe15+ 3l thresholds, we show that the relativistic effects are not so crucial in the energy range below the Fe15+ 3d threshold. The resonant states are identified and analyzed by using the resonance positions E r, effective quantum numbers n *, and widths Gr based on the idea of eigenphase gradients.