Chapter 2.6.1 - Electron and Positron Scattering by Atoms, Ions and Molecules

Abstract

This chapter reviews the theory of electron and positron scattering by atoms, ions, and molecules. Resonances play an important role in low-energy electron scattering by atoms and ions. There are two types of resonances—open channel or shape resonances and closed channel or Feshbach resonances. Shape resonances occurs when the effective potential between the electron and the target has a characteristic shape with an inner attractive well and an outer repulsive barrier, the latter usually caused by the centrifugal repulsion. Feshbach resonances occur for scattered electron energies just below excitation thresholds where the scattered electron is captured temporarily into a bound state with the target in an excited state. The chapter concludes with a discussion on electron scattering by molecules. The processes that occur in electron scattering by molecules are considerably more varied than those that arise in electron scattering by atoms and atomic ions because of the possibility of exciting degrees of freedom associated with the motion of the nuclei. Thus, along with electronic excitation and ionization, which also occur in electron atom scattering, additional processes that can take place include rotational and vibrational excitation, and dissociation and dissociative ionization.