Atomic data from the Iron Project

Abstract

Photoionization cross sections and dipole transition probabilities for the astrophysically important iron ion Fe IV are presented. The computations were car- ried out in the close coupling approximation using the R-matrix method including 31 LS terms with multiplicity (2S + 1) = 3 and 5 of the target ion Fe V. All quartets and sextet bound states of Fe IV with n 10 and L 8 are considered. The results include 746 LS bound states, dipole oscillator strengths for 34 635 LS transitions, and, for all bound states, detailed photoionization cross sec- tions with extensive resonance structures. These data dif- fer signicantly in many cases from the earlier data cal- culated under the Opacity Project and other theoretical calculations. In particular, the new cross section for the 6 S ground state of Fe IV exhibits a large resonance near the threshold that is not present in previous calculations and is likely to aect the eective photoionization rate signif- icantly. The autoionizing state that corresponds to that resonance as well as the Rydberg series to which it be- longs are identied through supplementary close coupling calculations.