ATOMIC DATA FROM THE IRON PROJECT .26. PHOTOIONIZATION CROSS-SECTIONSAND OSCILLATOR-STRENGTHS FOR FEIV

Photoionization cross sections and dipole transition probabilities for the astrophysically important iron ion Fe IV are presented. The compu tations were carried 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 less than or equal to 10 and L less than or equal to 8 ar e considered. The results include 746 LS bound states, dipole oscillat or strengths for 34 635 LS transitions, and, for all bound states, det ailed photoionization cross sections with extensive resonance structur es. These data differ significantly in many cases from the earlier dat a calculated under the Opacity Project and other theoretical calculati ons. In particular, the new cross section for the S-6 ground state of Fe IV exhibits a large resonance near the threshold that is not presen t in previous calculations and is likely to affect the effective photo ionization rate significantly. The autoionizing state that corresponds to that resonance as well as the Rydberg series to which it belongs a re identified through supplementary close coupling calculations.