IDENTIFICATION OF MECHANISMS OF ELECTRON-IMPACT DOUBLE IONIZING COLLISIONS BY E,(3-1)E EXPERIMENTS

We report e, (3 - 1)e experiments for the double ionization (DI) of argon at an incident energy of approximately 5.5 keV. Coincidence angular correlations of the two slow ejected electrons are measured at different ejection energies. The fourfold differential cross section distributions are consistent with a shake-off mechanism for the DI process. The utility of the method is discussed in terms of the different types of mechanisms for DI. It is shown that a suitable choice of the kinematic parameters may help to identify the DI process. Different successive interactions are discussed which result in double ionization with quite different angular correlations.