Distorted-wave calculations of dielectronic recombination cross sections in the Li isoelectronic sequence

The dielectronic recombination cross sections associated with the 2s→2p transition in the Li-like ions ${\mathrm{B}}^{2+}$, ${\mathrm{C}}^{3+}$, and ${\mathrm{O}}^{5+}$ have been calculated in the distorted-wave approximation. We compare calculated cross sections to selected doubly excited configurations of the type 2pnl in ${\mathrm{C}}^{3+}$ in pure LS coupling, intermediate coupling, and a configuration-average approximation. The LS-coupled results are about 33% low as compared to intermediate coupling for low and intermediate values of n and l, while the configuration-average approximation agrees quite well with the intermediate-coupled results for relatively low values of n or l, but tends to overestimate the intermediate-coupled cross sections at intermediate values of n or l. All three methods should agree at high values of n or l. In addition, we calculate the total cross sections associated with the 2s→2p excitation for all three ions using the configuration-average approximation, and we compare our results to merged electron-ion beam measurements of the cross sections for ${\mathrm{B}}^{2+}$ and ${\mathrm{C}}^{3+}$. The sensitivity of these cross sections to experimental conditions is also examined.