Dielectronic Recombination and Spectroscopy of the Heaviest Li-like Ions

Dielectronic recombination (DR) of very heavy Li-like ions including Pb⁷⁹⁺, Bi⁸⁰⁺, and U⁸⁹⁺ with Δn = 0 core excitations (1s²2s_1/2 → 1s²2p_1/2,3/2) has been investigated at the electron cooler of the Experimental Storage Ring (ESR) of GSI in Darmstadt, Germany. Absolute rate coefficients and resonance energies of DR via intermediate doubly excited Rydberg states 1s²2p_1/2 nℓ (n ≥ 20) and doubly excited states 1s²2p_3/2nℓ_j (n = 6 for Pb⁷⁹⁺ and Bi⁸⁰⁺, and n = 5 for U⁸⁹⁺) of recombined Be-like ions have been determined. For the 1s²2p_1/2 nℓ series Rydberg states up to n ≈ 50 were resolved in the measurement. In addition individual fine structure components of the Rydberg resonances can clearly be distinguished. For the first time in such a heavy system the series limit has directly been observed in DR. For these very heavy ions strong relativistic effects as well as the Breit interaction have to be taken into account in order to explain the experimental findings. The experimental data are compared with fully relativistic multi configuration Dirac Fock (DR/MCDF) calculations