Atomic Confinement

Abstract

We review the recent revival of interest in the subject of confined atoms, motivated by experimental developments in a number of areas, e.g. atoms under extreme pressure, atoms confined in zeolites, in bubbles, in solids, in quantum dots or trapped in molecular cages, as occurs in met- allofullerenes. The subject originated very early in the development of quantum mechanics, and even provided a theme for Arnold Sommerfeld in a birthday celebration in honour of Wolfgang Pauli. After this high point, it languished relatively unnoticed, except by a few practitioners who mostly used wavefunctions of confined atoms as a starting approximation to describe atoms in solids. The recent discovery of new forms of confinement demonstrates that concepts must be refined to bring out the rich diversity of effects expected in the spectroscopy of confined atoms. They allow atomic behaviour to be explored under novel circumstances, and provide a new bidge (alternative to cluster physics) from the atom to the solid. At present, metallofullerene targets are still difficult to manufacture with sufficient number density for ultraviolet and soft X-ray spectra to be probed. It is likely that this experimental problem will soon be resolved. Thus, the motivation already exists to predict what novel effects may occur and what their likely spectral manifestations will be. This should turn into a thriving new area.. Some current theoretical problems in the treatment of confined atoms will be described. A discussion of the recent classification of resonances in confined atoms into three different types will e presented. The influence of confinement on correlations will be indicated. Possible connections to the theory of EXAFS will be outlined.