Dynamics of single or double ionization of small systems from coincidence electron impact experiments

In this brief review, we illustrate the potentialities and the power of electron-electron coincidence studies to investigate the dynamics of single ionization SI [(e,2e) case] or double ionization DI [(e,3e) case] processes. An example for (e,2e) SI of rare gas atoms is presented with a new insight into the behaviour of the recoil versus the binary intensity. A second example for (e,2e) SI of molecules is used to illustrate the observation of a purely molecular effect, namely the signature of interference effects due to the two-center nature of the H2 molecule. The third example discusses an unprecedented triple coincidence study involving the scattered - ejected - Auger electrons emitted from an argon target. It is shown that the method allows to disentangle the contribution of various DI mechanisms.