IRON IONIZATION AND RECOMBINATION RATES AND IONIZATION EQUILIBRIUM

In the past few years important progress has been made on the knowledge of ionization and recombination rates of iron, an astrophysically abundant heavy element and a major impurity in laboratory fusion devices. Detailed calculations of ionization cross sections (direct and excitation autoionization process) and dielectronic recombination rate coefficients have now been performed for the whole iron isonuclear sequence. Crossed beam measurements of ionization cross sections are available for some iron ions. We make a critical review of the existing data on ionization and dielectronic recombination and present new computations of radiative recombination rate coefficients of Fe+14 through Fe+25 using the photoionization cross sections of Clark et al. We provide analytical fits to the recommended data (direct ionization and excitation-autoionization cross sections; radiative and dielectronic recombination rate coefficients). Finally we determine the iron ionic fractions at ionization equilibrium and compare them with previous computations as well as with observational data.