(E, 2E) Collisions

Abstract

The study of (e, 2e) collisions has expanded rapidly since the first coincidence measurements of the two emitted electrons in the electron impact ionization of helium. This chapter focuses on the symmetric (e, 2e) reaction at high and intermediate energies—that is, the regime of (e, 2e) collisions that can yield reliable information on the momentum distribution of the struck electrons for transitions to definite final ion states. This chapter deals with only those experiments designed to yield detailed information on the electronic structure of atoms and molecules. This is the regime of symmetric kinematics at intermediate and high electron energies. The chapter outlines some of the experimental techniques employed in these investigations. The basic theory necessary for describing the reaction mechanism and for extracting all the structure information is developed. The theory for atoms is extended to cover the case of molecular targets. The reaction mechanism at intermediate to high energies is investigated in the chapter for atomic targets in both the coplanar and noncoplanar symmetric geometry. Some of the structure information that has been obtained on atoms and molecules that include electron–electron correlation effects in both the target and final ion states are also discussed in the chapter.