Resonances in electron scattering and photon absorption

A short survey is given of the development of ideas about resonances in atomic scattering processes and their connection with the theory of resonant states in nuclei, impurity resonances in solids, ion-atom scattering and recombination in plasmas. A detailed discussion of the experimental situation for atomic resonances is then given, followed by a review of the theory of resonance reactions as applied to them. Special attention is given to effective range and quantum defect methods, and to Fano's configuration interaction theory. Theoretical results for line positions, shapes and widths are compared with experimental data and the need for more angular distribution data is emphasized.