Double photodetachment in He −: Feshbach and triply excited resonances

Abstract

We have investigated with unprecedented levels of detail K-shell photodetachment of metastable 1s2s2p 4P He − using a merged photon-ion beam apparatus. Our recent investigation allowed the first absolute cross-section measurement of the 2s2p 2 4P Feshbach resonance by way of a resonant simultaneous double Auger decay of unprecedented strength. In addition, higher resolution absolute cross-section measurements of triply excited resonances giving rise to hollow He − ion allowed a more stringent comparison with four different calculations.