PHOTODETACHMENT STUDY OF HE- QUARTET RESONANCES BELOW THE HE (N=3) THRESHOLDS

The photodetachment cross section of He- (1s2s2p P-4) has been measure d in the photon energy range 2.9-3.3 eV in order to investigate doubly excited states. Measurements were made channel specific by selectivel y detecting the residual He atoms left in a particular excited state f ollowing detachment. Three Feshbach resonances were found in the He(1s 2p P-3(o))+e(-) (epsilon p) partial cross section: a S-4 resonance bel ow the He(1s3s S-3) threshold and two P-4 resonances below the He(1s3p P-3(o)) threshold. The measured energies of these doubly excited stat es are 2.959 260(6), 3.072(7) and 3.264 87(5) eV. The corresponding wi dths are found to be 0.20(2), 50(5) and 0.61(5) meV. The measured ener gies agree well with recent theoretical predictions for the 1s3s4s S-4 , 1s3p(2 4)p and 1s3p4p P-4 states, respectively, but the widths devia te noticeably from calculations for 1s3p(2 4)P and 1s3p4p P-4 states.