| Photoionization cross sections and oscillator strengths for Fe IV |
| M.A. Bautista and A.K. Pradhan |
| Astronomy & Astrophysics Supplement Series, 1997, Vol.126, pp.365-371 |
Photoionization cross sections and dipole transition probabilities for the
astrophysically important iron ion Fe IV are presented. The
computations 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 
and 
are considered. The results include
746 LS bound states, dipole oscillator strengths for 34635 LS transitions,
and, for all bound states, detailed photoionization cross sections with
extensive resonance structures. These data differ significantly in many
cases from the earlier data calculated under the Opacity Project and other
theoretical calculations. In particular, the new cross section for the
S ground state of Fe IV exhibits a large resonance near the
threshold that is not present in previous calculations and is likely to
affect the effective photoionization rate significantly. The autoionizing
state that corresponds to that resonance as well as the Rydberg series to
which it belongs are identified through supplementary close coupling
calculations.