ENERGY SHARING (E,2E) COLLISIONS - IONIZATION OF HELIUM IN THE PERPENDICULAR PLANE

The authors report distorted-wave Born approximation (DWBA) calculations of the triple differential cross section for the process e-+He(1s 2) to e-+e-+He+(1s) in energy-sharing perpendicular plane geometry at incident energies from 34.6 to 200 eV. The cross section is given as a function of the angle phi between the two outgoing electrons. Their results reproduce well the pattern of corresponding experimental measurements of Woolf et al. (1989, 1990). A simple model analysis indicates that there should be a 'single scattering' peak at phi =180' and a 'double scattering' peak at phi =90'. In the double scattering mechanism the incident electron is first elastically scattered through 90' by the atom before ionising the target electron. At low energies single scattering should be dominant with double scattering taking over as the principal mechanism at high energies. Both DWBA and experiment confirm these predictions.