Role of dielectronic recombination and autoionizing states in the dynamic equilibrium of non-LTE plasmas

The dielectronic-recombination phenomenon is an essential component of the dynamical-equilibrium regime of non-LTE plasmas. This phenomenon is a sequence of two atomic processes, namely, resonant capture followed by spontaneous emission or collisional de-excitation. It relies on the existence of singly- and doubly-excited autoionizing states, which are blends of quasi-bound and continuum states. In most cases, a very large number of such states ought to be accounted for in the calculations of collisional-radiative models; however, for computational reasons it is necessary to consider level ensembles, namely electronic configurations, or superconfigurations. Formulas for the rates of resonant capture and autoionization are given for transitions between levels, between configurations, and between superconfigurations. Results of collisional-radiative calculations and comparisons between the effects of the different atomic processes are presented.