Recombination rates for Ti, Cr, Fe and Ni ions

Current status of the theoretical effort to evaluate the radiative recombination (RR) and dielectronic recombination (DR) rates for the Ti, Cr, Fe and Ni ions is reviewed. (i) A complete set of RR rates for all ions is given in the Z-scaled Coulombic representation, with improved formulas for the effective charge parameter. Using this result, sample RR rates are presented for Ti and Fe ions in several initial charge states. (ii) The DR data for ions with the number of electrons N=1, 2, 4 and 10, before capture, are summarized. Only partial data are available for ions with N=3, 5, 9, 11 and 12. There are serious gaps in the DR data for ions with N in the regions 5 < N < 9 and N > 12. The DR rates for ions in the gaps may be estimated using an approximate empirical rate formula, which is derived by fitting all the currently available results. The general trends of the rates as functions of temperature, core charge and the number of electrons are predicted by the rate formula. The effects of plasma environment on the rates, in terms of plasma microfield and density, are important but not incorporated into the rates presented here. (orig.)