We report the first measurements on radiative and dielectronic recombination (RR and DR) of very highly charged ions at energies ${\mathit{E}}_{\mathrm{cm}}$ as low as 0 to 50 eV. Novel techniques were employed at the heavy-ion storage ring ESR to obtain absolute recombination rates of ${\mathrm{Au}}^{76+}$(1${\mathit{s}}^2$2s). The increase of the RR rate for ${\mathit{E}}_{\mathrm{cm}}$→0 could be recorded and single DR resonances in ${\mathrm{Au}}^{75+}$(1${\mathit{s}}^2$2${\mathit{p}}_{3/2}$6${\mathit{l}}_{\mathit{j}}$) resolved. The experimental data allow sensitive judgement of calculations based on the Bethe-Salpeter approach to RR combined with results for DR from perturbative-relativistic, semirelativistic, and fully relativistic theories. Significant discrepancies are found only in the energy region of the 2${\mathit{p}}_{3/2}$6${\mathit{l}}_{3/2}$ resonances.

• Received 15 June 1992

DOI:https://doi.org/10.1103/PhysRevLett.69.2768