Correlation studies of excited states of the helium ion

The (e, 2e) and e, (3 - 1)e techniques have been used to study electron-impact single ionization of helium to the n = 1-4 ion states and double ionization, respectively. The measurements have been made at an incident electron energy of 200 eV under highly asymmetric kinematics. The n = 2 data show qualitatively similar features to previous higher energy asymmetric studies and can be explained qualitatively. The n = 3, 4 and double ionization data provide new theoretical challenges.