Non-perturbative vs. perturbative methods for photorecombination

Abstract

The vast majority of photorecombination cross sections available in atomic data bases have been computed using second-order perturbation theory. Numerous benchmarking studies comparing experimental measurements to these theoretical results have established their general validity, for total cross sections. Partial recombination cross sections, on the other hand, are more likely to exhibit strong interference effects, necessitating a higher-order theoretical treatment. While it is possible to include third-order terms and higher within perturbative methods, an appealing alternative is to use non-perturbative close-coupling techniques. The use of a radiative optical potential within the close-coupling method was first introduced by Robicheaux et al., and the general method was subsequently incorporated into the Belfast R-matrix codes to treat radiation-damped electron-impact excitation and photorecombination. This talk will focus on the implementation of the radiative optical potential R-matrix method for the computation of accurate photorecombination cross sections, and also on the comparison of these results to perturbative and experimental results. In particular, the general lack of interference effects in total recombination cross sections and the widespread importance of radiation damping on the computed cross sections will be demonstrated. In an interesting example, however, strong interference effects in the total cross section are found.