Radiation damping in highly charged ions: anR-matrix approach

Using an R-matrix code recently developed by Robicheaux et al which includes a radiative optical potential, we have calculated electron-impact excitation cross sections to the n = 2 levels of and . We focus on the resonance structure, which we find to be significantly damped even for low-lying resonances, and recent similar R-matrix calculations by Kisielius et al which omit radiation damping and significantly overestimate the resonance contribution. For dielectronic recombination resonances, we compare the extent of damping to a different R-matrix approach by Nahar and Pradhan, which uses the inverse of the photoionization process to calculate the radiative decay for low-lying resonances. It is demonstrated that the present method is superior for low-lying resonances, since the radiative width is incorporated in the total width for these resonances via the radiative optical potential.