Resonance and intermediate-coupling effects in electron scattering with highly charged ions. II. Autoionization and dielectronic recombination

The role of resonances in electron-impact excitation of highly charged ions is examined and some methods are described in order to take account of autoionization and dielectronic recombination. The intermediate-coupling calculations of paper I are extended to include these processes and effective collision strengths are obtained. Results are presented to illustrate particular features in a number of transitions in Fe²⁴⁺ and Mo⁴⁰⁺. Resonance analysis is carried out employing numerical interpolation techniques and multichannel quantum-defect theory, employing reactance matrices in nine-state close-coupling and distorted-wave approximations. It is shown that all three effects considered in the present study, departure from LS coupling, resonance enhancement due to autoionization, and reduction in autoionization enhancement due to dielectronic recombination, can be of considerable importance in the cross sections of highly ionized systems. In the high-Z ions of the helium isoelectronic sequence the contribution of autoionizing resonances remains large even after all probable radiative channels are included, although the net autoionization effect decreases with Z.