Influence of plasma density on the cross sections of radiative recombination to configuration-averaged excited nitrogen and oxygen atoms and ions

Abstract

Radiative recombination cross sections of all the charge states of nitrogen and oxygen ions are calculated in the central field and Hartree–Fock–Slater approximations. The recombining ions are considered on their ground states, to form recombined ions on different configuration-averaged excited states. The ion potential energies are calculated assuming electro-neutrality in a Wigner–Seitz cell containing bound and free electrons, and the effect of plasma density on the cross sections is investigated by varying the cell radius. When the plasma density increases up to 1020 cm−3, the bound and free wave functions are distorted which significantly impact the cross sections. These deviations from the free atom case are all the more significant as the ion charge state of the recombining ion is low and as the excitation energy of the recombined ion is high. Also, calculations of the radiative recombination rates allow for quantifying the impact of plasma density at different temperatures. It is shown, for temperatures greater than 1 (Ry), that the rates at low and high plasma densities are closed. Nevertheless, for temperatures lighter than 1 (Ry) the influence of plasma density on the rates is significant. In addition, transition probabilities between the bound levels of all the charge states of N and O are calculated, and the influence of plasma density on these probabilities is analyzed. These cross sections and rates may be used as entrance parameters in collisional-radiative models for fully ionized plasma simulations in the framework of studies concerning for example, switches in Marx generator and laser-induced plasmas in air.