A general formula for the profiles of 'giant resonances'

Abstract

The 'giant resonances' observed in atomic photoionisation are discussed in the context of scattering by a short-range attractive well. It is argued that they correspond to a scattering regime of the virtual states not usually probed in high-energy physics. In the shape-independent approximation, a general formula for the profile of a 'giant resonance' is derived and compared with experiment. A 'universal curve', connecting the breadth of a 'giant resonance' to its energy above threshold is also demonstrated from available data for free atoms.