(e,2e) in the vicinity of an autoionizing state as a 'perfect experiment' to measure parameters of the electron-impact ionization process

We consider the possibility of treating (e, 2e) experiments in the region of autoionizing resonances as 'perfect experiments' in which parameters relating to the direct and resonance ionization amplitudes can be determined. An angle-independent parameter is defined for the autoionization of a doubly excited s-state to the s-state of an ion. Experimental values of this parameter from recent data for decay of the (2s(2))S-I state of helium to the (1s)S-2 state of the helium ion are discussed. The more general situation involving states with L > 0 is outlined.