Mechanism of True Double Electron Capture by Multiply Charged Ions

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 nonautoionising configurations from the quasi-symmetrical one initially populated.