Unified treatment of electron-ion recombination in the close-coupling approximation

A unified treatment for electron-ion recombination has been developed and applied to detailed calculations for cross sections and total recombination rate coefficients for a number of atoms and ions. The ab initio calculations are carried out in the close-coupling approximation employing the R-matrix method for the bound and the continuum states of the electron-ion system. All final states of the recombined system are taken into account and the present method subsumes both the radiative and the dielectronic recombination (RR and DR) processes over all energy and temperature ranges of practical importance. Recombined states of the electron-ion system are divided into two groups: (a) n≤${\mathit{n}}_0$ and (b) ${\mathit{n}}_0$<n≤∞. Photoionization cross sections are calculated for all bound states of group (a), typically a few hundred bound states, referred to as low-n states, including a detailed energy resolution of the several infinite series of autoionizing resonances converging onto the various excited states of the core ion included in the close-coupling expansion. High-n states of group (b) are treated primarily through the theory of DR developed by Bell and Seaton [J. Phys. B 18, 1589 (1985)]. DR collision strengths with detailed resonance structures are presented.