Abstract
By measuring the yield of metastable atoms resulting from electron-impact excitation of helium, in the range of incident electron energy from 19.8 to 24.6 eV, the authors have obtained evidence for He- resonances in which both the excited electrons have high values of the principal quantum number. The resonances occur in distinct groups, the lower members of which form Rydberg series characterised by effective core charges that are nonintegral. Classification schemes for these resonances are discussed.