Ion–Atom Scattering Experiments: Low Energy

Abstract

This chapter outlines the physical principles and experimental methods used to investigate low energy ion–atom collisions. A low-energy collision is here defined as one in which the initial ion–atom relative velocity v is less than the mean orbital velocity ⟨v_e⟩ of the active electrons during the collision. For outer or valence electrons, ⟨v_e⟩ ≃ v_B, where $v_{\text{B}}={\mathrm{2.1877\times 10^{8}}}\,{\mathrm{cm/s}}$ is the Bohr velocity. In terms of the energy of a projectile ion, v_B corresponds to 24.8 ke V ∕ u.

The theory and results of ion–atom scattering studies are further discussed in other chapters of the book. The focus here is on the experimental techniques. Since several of these depend on the characteristics of a specific process, the following section presents a summary of the physics of low-energy ion–atom collisions.