Small Atomic and Molecular Clusters: Production, Properties, and Electronic Structure

Abstract

The clusters are relatively small aggregates of atoms or molecules, frequently in the gas phase. Clusters produced in this size range exhibit a number of properties that helped launch the field; they exhibit magic numbers in mass spectra and oscillations in their ionization potentials (IPs) and electron affinities (EAs). The magic numbers in particular led to some initial controversy as to their origin. Question arise whether they resulted from increased stability due to some geometric packing effect or rather because of a particularly stable electronic structure—that is, an electronically closed shell or whether the magic numbers were not because of stability, but to kinetic effects in the cluster production process. The answer turned out to be some of each. The oscillations in the IPs and EAs, on the other hand, indicated that particular cluster sizes would be more reactive than others and perhaps might point in the direction of good catalysts. Clearly then, important questions in this arena relate to stability, chemical reactivity, geometrical shape, and electronic structure. This chapter provides an overview of production, properties, and electronic structure of small atomic and molecular clusters.