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

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Abstract
The first complete set of unified cross sections and rate coefficients are calculated for photoionization and recombination of He- and Li-like ions using the relativistic Breit-Pauli R-matrix method. We present total, unified (e + ion) recombination rate coefficients for (e + C C ) and (e + C C ), including fine structure. Level-specific recombination rate 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 of Kα emission from the important He-like ions are pointed out. The overall uncertainty in the total recombination rates should not exceed 10%-20%. Ionization fractions for carbon are recomputed in the coronal approximation using the new rates. The present (e + ion) recombination rate coefficients are compared with several sets of available data, including previous LS coupling results and "experimentally derived" rate coefficients. The roles of relativistic fine structure, resolution of resonances, radiation damping, and interference effects are discussed. Two general features of recombination rates are noted: (1) the nonresonant (radiative recombination) peak as E,T → 0, and (2) the high-T resonant (dielectronic recombination) peak.

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