Photodetachment of 1s2s2p P-4 He- in the vicinity of the 1s threshold

A study of the photodetachment of the metastable 1s2s2p P-4 state of He- using multiconfiguration Hartree-Fock (MCHF) wavefunctions for bound states and Hartree-Fock plus configuration-interaction (HF + CI) continuum wavefunctions has revealed that the cross section is dominated by three features in the vicinity of the 1s threshold: a huge 2s2p(2) (hollow ion) resonance just below threshold; a large 30 Mb peak due to 1s detachment just above threshold and 1s detachment plus excitation a little way above threshold. No experimental investigation of this phenomenology, which differs markedly from 1s photoabsorption in neutral atoms, exists.