DIELECTRONIC RECOMBINATION FROM THE GROUND AND EXCITED-STATES OF C-4+ AND O-6+

We have calculated dielectronic recombination (DR) cross sections from the ground state (1 S1) and excited states (2 S3, 21S, and 2 P3) of the He-like ions C4+ and O6+ in the LS-coupling and intermediate-coupling approximations, using the program autostructure. We find the effects of configuration interaction, intermediate coupling, and external electric fields to be small. We compare our results with the recent high-resolution measurements of DR from the excited states of these ions by Andersen et al. [Phys. Rev. Lett. 62, 2656 (1989) and Phys. Rev. A 41, 1293 (1990)] by convoluting our cross sections with their electron velocity distribution. For the case of C4+, we obtain excellent agreement when we choose the 2 S3 to 2 S1 population ratio to be 18. For the case of O6+, we obtain good agreement with experiment with a 2 S3 to 21S population ratio of 70, except in the 6- to 8-eV energy region, where a model calculation indicates that coupling between resonances via the continuum may be important. By comparing experiment with theory, we have also estimated the metastable fraction of the 2 S3 term to be 70% in C4+ and 20% in O6+. The reason for this large difference is not understood. © 1990 The American Physical Society.