Photoionization and Recombination

Theoretically self-consistent calculations for photoionization and (e + ion) recombination are described. An identical eigenfunction expansion for the ion is employed in coupled channel calculations for both processes, thus ensuring consistently accurate cross sections and rates in an ab initio manner. The theoretical treatment of (e + ion) recombination subsumes both the non-resonant recombination (’radiative recombination’), and the resonant recombination (’di-electronic recombination’) processes in a unified scheme. In addition to the total, unified recombination rates, level-specific recombination rates and photoionization cross sections are obtained for a large number of atomic levels. Both relativistic Breit-Pauli, and non-relativistic LS coupling, calculations are carried out in the close coupling approximation using the R-matrix method. Although the calculations are computationally intensive, they yield nearly all photoionization and recombination parameters needed for astrophysical photoionization models with higher precision than hitherto possible, estimated at about 10-20% from comparison with experimentally available data (including ’experimentally derived DR rates’). Results are electronically available for over 40 atoms and ions. Photoionization and recombination of He-, and Li-like C and Fe are described for X-ray modeling. The unified method yields total and complete (e+ion) recombination rate coeffcients, that can not otherwise be obtained theoretically or experimentally.