  We study the ionization equilibrium of Fe using photoionization models that
incorporate improved values for the ionization and recombination cross-sections
and the charge-exchange rates for the Fe ions. The previously available
photoionization models predict concentrations of Fe3+ which are a factor of 3-8
higher than the values inferred from emission lines of [Fe III] and [Fe IV].
Our new models reduce these discrepancies to factors of 2-5. We discuss the
possible reasons behind the remaining discrepancies and present an updated
ionization correction factor for obtaining the Fe abundance from the Fe++
abundance.
