Effects of quantum interference between radiative and dielectronic recombination on photorecombination cross-section profiles for the He-like ionsAr16+andFe24+

Abstract

Total cross sections for electron-ion photorecombination (PR) processes are calculated using a projection-operator and resolvent-operator approach. This approach provides a unified quantum-mechanical description of the combined electron-ion PR process, including radiative and dielectronic recombination as coherent, interfering components. An especially adapted version of the Hebrew-University Lawrence-Livermore Atomic Code HULLAC is developed and employed for the calculations. In particular, PR cross sections for He-like argon and iron ions are calculated for incident-electron energies in the vicinity of the ${1s2l2l}^{\ensuremath{'}}$ and ${1s2l3l}^{\ensuremath{'}}$ doubly-excited, autoionizing levels of the Li-like ions. Significant effects of quantum interference between radiative and dielectronic recombination, in the form of asymmetric PR cross-section profiles, are predicted, especially for weak transitions. The general behavior of the interference effect, as a function of the ion charge q and as a function of the principal quantum number ${n}^{\ensuremath{'}}$ of the outer electron in the autoionizing state, is investigated using a hydrogenic-scaling analysis. It is found that the degree of asymmetry in the PR cross-section profile can be substantial for close-to-neutral ions and also for very highly-charged ions. In the intermediate-charge regime, on the other hand, the asymmetry is anticipated to be less prominent. The dependence of the quantum-interference effect on ${n}^{\ensuremath{'}}$ is predicted to be much weaker.