Double Ionization Mechanisms from Triple Coincidence Experiments

Abstract

Differential studies of the double ionization (DI) process, both under photon and charged particle impact, have known a remarkable development in the last few years, due to major technical advances in multianalysis and multidetection systems, and the use of multiparameters coincidence spectrometers. An important issue of these studies is to investigate the electronic correlations, i.e. the correlated motion of the electrons, both in the initial state and in the final state of the collision. For instance, it is the initial state electron correlation which is responsible¹ for the photon impact DI, and this largely prevails also under electron impact. Moreover, the asymptotic angular distribution of the products is largely dominated² by the final state correlations, that is the Coulombic interactions between the outgoing particles. Therefore, an (e,3e) experiment where three electrons and one doubly charged ion are present in the continuum is expected to yield unique information towards understanding the solution of the 3-and the 4- body problems for which exact solutions are not yet known. Main objective of this work is placed along these lines, with a special emphasis being put on understanding which particular mechanism is responsible for the electron impact double ejection of two electrons from the target into the continuum. In other words, we would like to answer the question: is the electron impact DI due to a direct process, or does it proceed via the electron correlations ? We will see that the (e,3e) experiments may enable disentangling between various competing DI processes.