Electron‐Ion Recombination Rate Coefficients and Photoionization Cross Sections for Astrophysically Abundant Elements. IV. Relativistic Calculations for C iv and C v for Ultraviolet and X‐Ray Modeling

The first complete set of unified cross sections and rate coefficients arecalculated for photoionization and recombination of He- and Li-like ions usingthe relativistic Breit-Pauli R-matrix method. We present total, unified (e +ion) recombination rate coefficients for (e + C VI ---> C V) and (e + C V\longrightarrow C IV) including fine structure. Level-specific recombinationrate coefficients up to the n = 10 levels are also obtained for the first time;these differ considerably from the approximate rates currently available.Applications to recombination-cascade coefficients in X-ray spectral models ofK-alpha emission from the important He-like ions is pointed out. The overalluncertainty in the total recombination rates should not exceed 10-20%.Ionization fractions for Carbon are recomputed in the coronal approximationusing the new rates. The present (e + ion) recombination rate coefficients are compared withseveral sets of available data, including previous LS coupling results, and`experimentally derived' rate coefficients. The role of relativistic finestructure, resolution of resonances, radiation damping, and interferenceeffects is discussed. Two general features of recombination rates are noted:(i) the non-resonant (radiative recombination) peak as E,T ---> 0, and the (ii)the high-T resonant (di-electronic recombination) peak.Comment: 38 pages, 10 figures, submitted to Astrophys. J. (Suppl