Dielectronic recombination at low energies: Spectroscopy of doubly excited states in beryllium-like Na7+ ions

Abstract

Absolute rate coefficients for the dielectronic recombination (DR) of Na8+ ions producing doubly excited states in beryllium-like Na7+ have been measured at the Heidelberg heavy-ion test storage ring (TSR). The investigated electron energy range covers all DR resonances related to 2s→2p1/2 and 2s→2p3/2 Δn=0 core excitations. Resonances related to Δn=1 and Δn=2 transitions of the valence electron are found at relative energies between 50 and 250 eV. At very low energies the resonance group associated with Na7+ (1s22pj7lj′) intermediate states has been investigated with an energy resolution and precision that will challenge state-of-the-art theory.