Dielectronic Recombination (via N = 2→ N ′ = 2 Core Excitations) and Radiative Recombination of Fe xx : Laboratory Measurements and Theoretical Calculations

Abstract

We have measured the resonance strengths and energies for dielectronic recombination (DR) of Fe XX forming Fe XIX via N=2-->N'=2 (ΔN=0) core excitations. We have also calculated the DR resonance strengths and energies using the AUTOSTRUCTURE, Hebrew University Lawrence Livermore Atomic Code (HULLAC), Multiconfiguration Dirac-Fock (MCDF), and R-matrix methods, four different state-of-the-art theoretical techniques. On average the theoretical resonance strengths agree to within ~30%, which is significantly larger than the estimatedrelative experimental uncertainty of ~1 eV, which includes the predicted formation temperatures for Fe XX in an optically thin, low-density photoionized plasma with cosmic abundances, the experimental and theoretical results agree to better than ~15%. This is within the total estimated experimental uncertainty limits of 2p3/2 core excitations. We have also used our R-matrix results, topped off using AUTOSTRUCTURE for RR into J>=25 levels, to calculate the rate coefficient for RR of Fe XX. Our RR results are in good agreement with previously published calculations. We find that for temperatures as low as kBTe~10-3 eV, DR still dominates over RR for this system.