  Relativistic close coupling calculations are reported for unified electronic
recombination of (e + C IV) including non-resonant and resonant recombination
processes, radiative and dielectronic recombination (RR and DR). Detailed
comparison of the theoretical unified results with two recent experiments on
ion storage rings (Mannervik etal. [1] and Schippers etal. [2]) shows very good
agreement in the entire measured energy region 2s -- 2p with 2pnl resonances.
The results benchmark theory and experiments to uncertainties of ~15%, and show
that the resonant and the background cross sections are not an incoherent sum
of separate RR and DR contributions. The limiting values of the DR cross
sections, as n ---> infinity, are shown to correspond to those due to electron
impact excitation (EIE) at the 2Po_(1/2,3/2) fine structure thresholds,
delineated for the first time. The near-threshold 2s 2S_(1/2) - 2p
2Po_(1/2,3/2) EIE cross sections are also compared with recent experimental
measurements. The demonstrated threshold fine structure and resonance effects
should be of general importance in excitation and recombination of positive
ions.
