FINE-STRUCTURE RESOLVED DIELECTRONIC RECOMBINATION RATES FOR THE N=3 EXCITED CONFIGURATIONS OF FE-XVI-FE-XIX

Spectroscopic analysis of X-ray emission lines from hot astrophysical plasmas. such as solar and cosmic X-ray sources, is a powerful tool in the determination of elemental abundances and temperature and density diagnostics of the emitting gas. This same analysis can be used to model high-temperature laboratory plasmas associated with magnetic and inertial confinement fusion as well as with the study of X-ray laser research. Accurate determination of atomic rates is crucial for a reliable analysis. Dielectronic recombination is the dominant recombination process for incompletely ionized plasmas. The rate coefficients for dielectronic recombination of several ionization stages of the astrophysically abundant element iron (Fe XVI-Fe XIX) are presented at the fine-structure levels of the n = 3 excited states at several temperatures. The rate coefficients are calculated for a Maxwellian electron distribution in a low-density corona approximation. The dielectronic recombination process involves a large number of doubly excited states of the recombined ions and computations of many radiative as well as autoionization rates from these states. In this calculation we include doubly excited states that are formed by the free electron captured up to very high Rydberg states and detailed calculations of all possible dipole allowed radiative transitions and all dipole as well as nondipole autoionization transitions. Transitions to excited states of the recombining ion from all open autoionization channels, which have a significant effect in reducing the rate coefficients (as presented in the works of Jacobs et al.), are also included in our calculations. These calculations were carried out in the isolated resonance approximation using the Hartree-Fock method with relativistic corrections (as described by Cowan). The dielectronic recombination rate coefficients were evaluated at many temperatures encompassing the range around the temperature of maximum abundance. These J-resolved data will be extremely useful for accurate ionization balance calculations for astrophysical as well as laboratory iron plasmas.