Showing papers in "Chemical Reviews in 1969"

Small free negative ions

Abstract: This article surveys the restricted subject of properties of isolated atomic and small molecular negative ions. By so defining our subject, we include in our discussion electron affinities, electronic states, and optical properties, and the experimental and theoretical methods for studying these properties. We exclude from our discussion the vast group of problems associated with large polyatomic negative ions and with most of the rich subject of collision processes involving negative ions, such as detachment and transfer of electrons in collisions. Such a choice means that roughly we cover those aspects of negative ion chemistry that are related to thermodynamics and to astrophysics, the aspects that depend on equilibrium properties and on the interaction of isolated negative ions with radiation. The aspects we omit are those pertinent to gaseous discharge physics, to radiation damage problems, and to the study of ion-molecule reactions. Our emphasis is primarily on assessing the state of our knowledge of the properties, of the level of precision and accuracy of this knowledge, and of how the information is obtained. At present, the larger part of our most accurate information about negative ions comes from experiments rather than from theory. Moreover, the theoretical methods for studying properties of these ions are essentially the same as those for studying neutrals or positive ions, while the experimental methods are considerably more specialized and sometimes almost unique. We therefore dwell considerably more on the experimental methods than on the theoretical, and in general simply cite the theoretical results and methods.