Negative Ions

Abstract

This chapter provides a review of negative ions. This chapter starts with a brief discussion on the ground states of negative atomic ions and involves determination of atomic electron affinities for several elements. All the methods used for this depend on the determination of the small difference between two directly calculated large numbers. In principle at least it would be an advantage if the small difference could be calculated directly. The chapter also discusses excited states of atomic negative ions and electron affinities and structures of negative molecular ions—for example, diatomic and polyatomic ions. The chapter covers dissociative attachment that has continued to engage the attention of many research groups both experimental and theoretical. On the experimental side, the work can be classified into three main categories: (1) measurements at room temperature of total dissociation cross sections as a function of electron energy for further molecules as well as with increased energy resolution for molecules previously investigated, (2) measurement of differential cross sections including the angular distributions of the product ions, and (3) the effect of initial vibrational or rotational energy excitation on the rate of dissociative attachment. The chapter explains photodetachment and photodissociation, ionic reactions at thermal and epithermal energies, ionic reactions at high energies and closes with a discussion on negative ions in electric discharge and breakdown phenomena.