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

Abstract

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 ~ no and (b) no < n ~ 00. 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, 1589Phys. B 18, (1985]. DR collision strengths with detailed resonance structures are presented. The detailed and the resonance-averaged DR collision strengths show characteristic peaks at the target thresholds of the core ion corresponding to dipoleallowed transitions. Individual bound states of the e +ion system with dominant contribution to lowenergy recombination are described. The present results demonstrate the importance of (i) recombinations to excited states (particularly the metastable states), and (ii) low-energy autoionizing resonances, both of which result in large contributions to effective electron-ion recombination. The individual contributions of the excited bound states of the e + ion system are calculated and their relative contribution to the total are discussed. The general pattern of the recombination rate, as a function of electron temperature, is studied along an isoelectronic sequence. It is found that while the low-energy (temperature) recombination increases with ion charge z, the relative high-energy (temperature) contribution to the total decreases; i.e., viewed as independent processes, the RR part increases while the DR decreases with z. Total recombination rate coefficients for several atoms and ions (C II, S II, C II, N II, 0 III, F IV, N e v, and Si IX) are obtained over the entire temperature range of possible interest in applications. Comparisons are made with earlier works on RR and DR. PACS number(s): 34.80. Kw, 32.80.Dz, 32.80.Fb

Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions

“…Experimentally, much progress has been made due to the use of ion storage rings and electron-beam ion traps (EBITs) [21][22][23]. On the theory side, a number of computational approaches have been used successfully to describe DR for many simpler ions and to produce data for plasma modelling (see [24][25][26][27][28][29][30][31][32][33][34] and references therein). For more complex targets such as Au 25+ , U 28+ , or W 20+ considered in this work, conventional DR calculations underestimate the measured recombination rates, particularly at low incident-electron energy [17,35].…”

Photoevaporation of Protostellar Disks. V. Circumstellar Disks under the Influence of Both Extreme‐Ultraviolet and Far‐Ultraviolet Radiation

“…It is an approximation for gas temperatures between T \ 10È104 K of the results obtained by Nahar & Pradhan (1994), including both radiative and dielectronic recombination of carbon. The electron density consists of contributions from n e \ nx ] n C x C the ionization of hydrogen and carbon, where x is the degree of ionization of hydrogen and n the total particle density.…”

Photoionization and electron-ion recombination of Cr I

“…Cr I is studied using the unified method [5,6] which is based on the close-coupling (CC) approximation and R-matrix method implemented under the Opacity Project (OP) [7] and the Iron Project (IP) [8]. A brief outline of the theory relevant to the present calculations is given below.…”