The relative, coplanar angular distributions of electrons, produced in an electron-impact double ionization of helium (e, 3e reaction), have been measured 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 general features of the angular distributions are discussed. The data are analysed in different angular modes which allows a detailed comparison with state-ofthe-art calculations. For high incident energy and small momentum transfer, 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 compare the present findings with the PDI and identify the contribution of non-dipole effects.

Differential cross-sections are measured for autoionising double capture (ADC) and true double electron capture (TDC) in collision of multiply charged ions with rare-gas targets. Angular profiles and energy gain spectra are identical for both processes suggesting a similar primary mechanism. ADC is well understood in the framework of the independent electron model. To populate TDC a secondary mechanism is suggested which involves electron-electron interaction and feeds very asymmetrical nonautoionbing conf5gurations from the quasi-symmetrical one initially populated.

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Two-electron capture by slow multiply charged ions colliding on rare-gas targets at keV energies populates doubly excited states of the projectile with large cross sections. Though these states are dominantly autoionizing, important radiative decay following double capture have been reported, among which the direct observation of the fluorescence from Rydberg states. These findings are important since they modify the charge and radiation balance of the multiple charge exchange reactions. A mechanism based on post-collisional effects was proposed, in which Rydberg states are fed from the quasi-symmetrical doubly excited states initially populated. A quantitative analysis of this effect is developed leading to a simple model which is applied to N7+ on He and Ar collisions. The evolution of the competition between autoionization and fluorescence yields of the Rydberg states with the internuclear distance is emphasized.