The energies of the triply excited n=2 intrashell He- resonances 2s(2)2p and 2s2P(2) revisited

Using a recently constructed high-resolution crossed-beam apparatus consist ing of a hemispherical electron monochromator and a quadrupole mass spectro meter, we have measured in detail the He+ ionization cross-section function in the electron energy range from similar to 56-59 eV. By fitting the two structures corresponding to the presence of the two triply excited n = 2 in trashell He- resonances (2s(2)2p)P-2 and (2s2p(2))D-2 with the theoretical natural line shape, we have deduced that their energy positions lie at 57.0 6 +/- 0.05 and 58.15 +/- 0.05 eV, respectively. Between these two states, a n additional previously unseen structure has been observed and tentatively linked to the doubly excited autoionizing (2S(2))S-1 state of He. When comp aring the presently deduced resonance energies with previous data, there is good agreement within the error bars with those experiments which used bot h a similar experimental technique to detect these states and a data analys is based on the Fano line shape. Experimental results using other methods t o detect and characterize these states (electron scattering, electron excit ation) appear to lie at slightly higher energies; nevertheless, the energy separation between the two states is the same for almost all experiments. ( C) 2001 Elsevier Science B.V.