Coulombic Entanglement: Two-Step Double Photoionization of Atoms

Abstract

Unlike in the previous Chap. 5, an atom or a molecule may lose two of its electrons in two consecutive steps as well (e.g., Fig. 3.1). While its primary ionization (i.e., loss of first electron) is caused from the energy supplied by some external source, the secondary ionization (i.e., emission of second electron) takes place in the rearrangement of electrons resulting from the primary ionization. Such a rearrangement of electrons becomes necessary whenever an inner-shell electron leaves the target in latter’s primary ionization. However, it is equally possible that such a rearrangement may lead to the emission of a photon in place of an electron (e.g., Fig. 3.2). This loss of energy in the form of a photon by, or departure of an electron from, an atom or a molecule due to rearrangement of its constituents is known as spontaneous radiative or non-radiative decay, respectively. The non-radiative decay was first observed by Auger [73, 74, 175, 176, 261]. The secondary ionization is, therefore, also known as Auger decay and the emitted particle called an Auger electron, say, e _a. In this monograph, we will consider the primary ionization due only to the absorption of a single photon and, hence, the emitted particle will be known as a photoelectron e _​p (say).