Radiation damping of autoionizing resonances

Abstract

Radiative decay of resonances is investigated in detail for electron - ion recombination cross sections of He-like ions of carbon and iron. Relativistic close-coupling calculations are carried out using the Breit - Pauli R-matrix method, combined with a perturbative treatment for radiative and autoionization decay, as well as with the relativistic distorted-wave method. Good agreement is found with the synchrotron-storage ring experimental data for C V by Mannervik et al, and the electron-beam ion-trap data for Fe XXV by Beiersdorfer et al. Radiation damping is considerably more significant for Fe XXV than C V; however, contrary to claims by Gorczyca and Badnell and Robicheaux et al, it is unlikely to be of importance in general since the radiative decay rates are orders of magnitude smaller in atomic species other than the He-like and the H-like ions.