Photorecombination of lithium-like Sc18+ at threshold: a challenge for atomic structure theory

Absolute rates for photorecombination (PR) of lithium-ac Sc18+ ions have be en measured at the Heidelberg heavy-ion Test Storage Ring (TSR). The invest igated electron energy range covers all DR resonances related to 2s --> 2p( 1/2) and 2s --> 2P(3/2) Deltan = 0 core excitations. Resonances associated with 1S(2)2p(3/2) 10l(j) intermediate states are found at energies between 0 and 0.3 eV. They are measured with an energy resolution reaching down to about 18 meV for the lowest-energy resonances. A comparison between the exp erimental results and calculations based on relativistic many-body perturba tion theory (RMTB) yields a good agreement even though deviations at very l ow energy could not be explained yet.