Relativistic radiatively damped R-matrix calculations of the electron-impact excitation of helium-like iron and krypton

Abstract

Electron-impact excitation data for He-like ions are of significant importance for diagnostic applications to both laboratory and astrophysical plasmas. Here we report on the first fully relativistic R-matrix calculations with radiation damping for the He-like ions Fe24+ and Kr34+. Effective collision strengths for these two ions have been determined with and without damping over a wide temperature range for all transitions between the 49 levels through n = 5. We find that damping has a pronounced effect on the effective collision strengths for excitation to some of the low-lying levels, but its effect on excitation to the vast majority of levels is small. At the energy of a resonance peak, we also investigate the effect of radiation damping on the angular distribution of scattered electrons. Finally, we compare our results for Fe24+ with an earlier intermediate coupling frame transformation R-matrix calculation with radiation damping by Whiteford et al (J. Phys. B: At. Mol. Opt. Phys. 34 3179) and find good agreement, especially for excitation to the lower levels.