Complete experiments for the double ionization of He: (e, 3e) cross sections at 1 keV impact energy and small momentum transfer

The relative, coplanar angular distributions of electrons, produced in an e lectron-impact double ionization of helium (e, 3e reaction), have been meas ured at 1. 1 keV impact energy. The momentum transfer was 0.45 au. and the two 'ejected' electrons were detected with the same energy of 10 eV. The ge neral features of the angular distributions are discussed. The data are ana lysed in different angular modes which allows a detailed comparison with st ate-of-the-art calculations. For high incident energy and small momentum tr ansfer, as in the present case, the (e, 3e) cross section can be related to the single-photon double ionization (PDI). We exploit this fact and compar e the present findings with the PDI and identify the contribution of non-di pole effects.