Autoionizing high-Rydberg states of very heavy Be-like ions: A tool for precision spectroscopy

Autoionizing high-Rydberg states formed during the initial electron capture phase of dielectronic recombination (DR) provide a unique access to spectroscopic information of highly charged heavy ions. This paper summarizes recent experimental and theoretical studies on the low energy 1s22pjnlj' (j=1/2, 3/2) Be-like DR resonances associated with the 2s1/2→2pj core excitations of the Li-like ions 19779Au76+, 20892Pb79+ and 23892U89+. An extrapolation of the resonance energies of the 1s22p1/2nlj' (n≥20) Rydberg series to the series limits (n→∞) yields the 2s1/2-2p1/2 transition energies. The experimental precision of below 100 meV for all three ions obtained with this photonfree spectroscopic method is comparable to the best optical measurements available and allows to test quantum electrodynamics of strong central fields on a level of below 7% of the α2 contributions. Furthermore, our theoretical calculations show that the observed DR resonance positions sensitively depend on the charge distribution within the atomic nucleus