Studies of autoionization with (e,2e) spectroscopy

Abstract

Recent advances in the study of double excitation-autoionization processes in helium using the (e,2e) technique are reviewed. Experiments at Flinders (Australia) and Newcastle (UK) provide the first reliable experimental data and have provoked the development of new theoretical approaches to the problem. Comparisons with recent calculations of the coincident electron spectra and parameters characterising the resonance states are presented for different kinematic conditions. Since the resonance parameters contain complex amplitudes relating to the resonance excitation, and direct and resonance ionization, they are extremely sensitive to the dynamics of the reaction and the atomic structure. Hence they provide the most rigorous test of the theory of ionization by electron impact.