Effects of postcapture electron-ion collisions on dielectronic recombination demonstrated on Ne-like ions

A model is introduced for investigating the effect of electron-ion inelastic collisions on dielectronic recombination (DR) and for predicting its electron-density dependence. A general method for obtaining effective DR rate coefficients for optically thin dense plasmas is described. Level-by-level relativistic calculations are performed for DR of Ne-like iron, selenium, and tungsten in their ground state via the Na-like 1s(2)(2s2p)(7)3l n' l' (n' = 3,4) autoionizing configurations. The results clearly show that, as the electron density increases, the first density effect to appear is an enhancement of the DR rates through collisional transitions among the autoionizing levels. At higher densities, collisional stabilization and collisional ionization play an important role. At low electron temperatures, collisional stabilization processes enhance the DR rates, whereas at high temperatures, collisional ionization reduces them. However, in a relatively wide intermediate temperature range, the opposite contributions of the various collisional mechanisms can result in a very small total collisional effect. Additionally, it is found that all of the various collisional effects strongly decrease with the ion charge. For very highly charged ions, such as Ne-like W, the collisional effect is appreciably quenched, even at very high densities, due to the dominance of the radiative processes.