Effects of collisions on level populations and dielectronic recombination rates of multiply charged ions
Abstract
A generalization of previously reported statistical theories is developed for determining the excitedlevel populations and the ionizationrecombination balance of multiply charged atomic ions in an optically thin hightemperature plasma. Account is taken of the most important collisional and radiative processes involving bound and autoionizing levels in three consecutive ionization stages. We obtain a set of rate equations for the population densities of the lowlying levels which contains effective excítation, ionization, and recombination rates describing indirect transitions through the more highly excited bound and autoionizing levels. The familiar coronamodel equations for the groundstate populations are recovered by making the assumption that all excited states decay by only spontaneous radiative or autoionization processes. When collisional processes become efficient in depopulating the highly excited levels important in dielectronic recombination, the effective rate of recombination must be described by a collisionaldielectronic recombination coefficient. Results of calculations are presented for the collisionaldielectronic recombination rate coefficients for recombination of Fe^{+8}Fe^{+13} ions. At an electron density of 10^{16} cm^{3}, dielectronic recombination is still the dominant recombination process. However, the collisionaldielectronic recombination rate coefficients are found to be reduced by about an order of magnitude from their coronamodel values due to the effects of multiplecollisional excitations on the populations of the highly excited bound levels of the recombined ion. The dielectronic recombination rates into these highly excited levels are found to be enhanced by the effects of collisionally induced angular momentum redistribution on the populations of the autoionizing levels.
 Publication:

Physical Review A
 Pub Date:
 August 1978
 DOI:
 10.1103/PhysRevA.18.697
 Bibcode:
 1978PhRvA..18..697J