We have calculated dielectronic recombination (DR) cross sections from the ground state (1 'S) and excited states (2'S, 2'S, and 2'P) of the He-like ions C + and 0 + 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 C +, we obtain excellent agreement when we choose the 2'S to 2 'S population ratio to be 18. For the case of 0 +, we obtain good agreement with experiment with a 2'S to 2 'S population ratio of 70, except in the 6to 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'S term to be 70%%uo in C + and 20% in 0 +. The reason for this large difference is not understood.

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The effects of external electric fields on Ln =0 dielectronic recombination {DR) rate coefficients for O~+, q =1, . . . , 5 are calculated using a configuration-average distorted-wave approach. Fieldionization effects lead to a decrease in the DR rate coefficient while field-mixing effects lead to an increase in the DR rate coefficient. Overall, strong fields produce a significant decrease in the DR rate coefficient at the peak temperature, i.e. , by over a factor of 10 for several oxygen ions. The configuration-average distorted-wave results are also compared with the Burgess general formula II [A. Burgess (private communication)] that includes both field-mixing and ionization effects It . is found that this formula roughly models these effects, and some guidelines as to the range of validity of this simple-to-use formula are developed. In the limit of zero external electric fields, the distorted-wave approach is further compared with recent sophisticated configuration-mixing intermediate-couplingcalculations as well as with the Burgess general formula I [A. Burgess, Astrophys. J. 141, 1588 (1965)].