Dielectronic recombination in plasmas: the final state distribution

The dielectronic recombination rate is one of the important input parameters to rate equations for modeling plasmas, where the excited state population of the plasma ions is determined by taking into account the radiative and collisional effects of plasma particles. The rates are often conveniently summarized in the form of empirical formulas to facilitate their use; in particular, properly designed rate formulas are needed that describe the electron capture to the individual singly excited final recombined states. However, the currently available rate formulas fail to meet this requirement, although they are obtained from more detailed benchmark calculations that explicitly include all the important transitions. The modified rate formulas may be obtained by keeping separate the rates to the individual singly excited final states, but still summing the contributions from different intermediate resonance states, with proper account of the cascades. Ne-like Al3+ ions in their ground state are used as examples to show that the rates to the final ground state are reduced by as much as a factor of 5 from the total rates.