Dielectronic Recombination in O$^{4+}$ Above and Below the Ionization Threshold

Relativistic perturbation theory calculations are carried out for O$^{4+}$ $1s^2 2s^2$ + e -> O$^{3+}$ $1s^2 2p^2 3l (l=0,1,2)$ dielectronic recombination. We find that 37 of the 57 levels in the $1s^2 2p^2 3l$ configurations lie above the O$^{4+}$ ionization limit. The largest cross sections are found at 1.7 eV for the $1s^2 2p^3 3d$ configuration.