Influence of metastable states and thermal equilibration upon dielectronic recombination in low- to moderate-density plasmas

The decrease of the dielectronic recombination rate coefficient by the thermal equilibration of the highly excited, bound final states produced by the recombination process with the plasma electrons is examined for the oxygen isoelectronic sequence. The potential enhancement of the effective rate of dielectronic recombination by the presence of metastable states in the ground configuration of the initial ion is analyzed for ${\mathrm{Fe}}^{18+}$. The net effect of these two processes upon the dielectronic recombination rate coefficient of ${\mathrm{Fe}}^{18+}$ is a 5–10 % enhancement from 0.8 keV to higher temperatures at plasma densities of ${10}^{14}$ electrons/${\mathrm{cm}}^3$, and a maximum 40% decrease at lower temperatures where Δn=0 radiative stabilizing transitions dominate the dielectronic recombination process.