The photoionization of Fe7+ and Fe8+ in the 2p–3d resonance energy region

Abstract

The photoionization cross sections of the levels belonging to the ground configuration [Ne]3s23p63d of Fe7+ and [Ne]3s23p6 of Fe8+ have been investigated using the fully relativistic R-matrix method in the 2p–3d excitation region. The detailed resonance structures are described and analysed in some detail with the resonance positions, widths and oscillator strengths being determined. To identify the resonances, the transition energies and oscillator strengths are calculated by the multi-configuration Dirac–Fock method implemented by the GRASP code as well. The cross sections have also been obtained using the non-relativistic R-matrix calculations. The resonances in the relativistic calculation span a much broader energy region than the non-relativistic result. For an iron plasma at a temperature of 20 eV and a density of 0.004 g cm−3, which is a typical experimental condition recently carried out by Chenais-Popovics et al (2000 Astrophys. J. Suppl. Ser. 127 275), the autoionization widths of the 2p–3d resonances are much larger than the widths caused by the radiative lifetime and electron impact broadening, while the Doppler widths are smaller than but rather close to the autoionization widths.