ELECTRONIC-STRUCTURE INFORMATION FROM ELECTRON-IMPACT IONIZATION EXPERIMENTS

Electron impact ionisation with full determination of the kinematics ( measurement of energies and momenta of the incident, scattered and eje cted electrons) has proven to be useful for investigating both the ele ctronic structure of atoms and molecules and the mechanism of ionisati on. These experiments are, by definition, coincidence experiments sinc e it is necessary to be sure that all the detected electrons originate from the same collision. For single-electron ionisation, (e, 2e), the emphasis has been on momentum densities and spectroscopic factors-see for example Coplan et al. (1994), McCarthy and Weigold (1976, 1988, 1 991) and Leung (1991). For double ionisation, (e, 3e), data are just b eginning to emerge, with early results on the Auger process and direct double ionisation (Duguet and Lahmam-Bennani 1992). Both (e, 2e) and (e, 3e) experiments are technically challenging because the signals ar e small and there is usually a large background. In the last few years , electrostatic spectrographs and position sensitive detectors have im proved the resolution and precision of (e, 2e) measurements and have m ade (e, 3e) measurements a practical reality.