Atomic data for opacity calculations: XX. Photoionization cross sections and oscillator strengths for Fe II

Abstract

Large scale ab initio calculations for the radiative data of Fe II have been carried out in the close coupling (cc) approbation employing the it-matrix method and a target state expansion consisting of 83 LS terms of Fe III. All bound states of Fe II with n ≤ 10 and l ≤ 7 are considered. The results include 1301 bound states in LS coupling, oscillator strengths for 35 941 transitions among the bound LS states, and detailed photoionization cross sections for all bound states. Autoionizing resonances, as well as the coupling to excited core states, enhance the photoionization cross sections substantially. The calculations of oscillator strengths have been extended beyond the requirement of the Opacity Project to include a large number of fine structure transitions in Fe II, using an algebraic transformation of the LS coupled line strength and the observed energies. The present ƒ- values compare favourably with available experimental values and the calculations by Kurucz. However, the present results differ considerably from earlier 16-state R-matrix calculations and the new radiative data yield Rosseland mean opacities that are 50% higher. Some special features in the monochromatic opacity spectra of Fe II are also noted.