Quantum defect theory X. Photoionization

Abstract

Photoionization cross sections are expressed in terms of quantities which vary slowly as functions of energy, and known functions which may vary rapidly. The theory is applied to photoionization of Be, with inclusion of the Be⁺ 2s and 2p states. The slowly varying functions are computered at energies above the 2p threshold and extrapolated to the resonance region below the threshold. A parametric form is obtained for the calculation of resonance structures this is superior to the form obtained by Fano (1961) for the case in which the widths of the resonances are comparable with the separation of resonances in a Rydberg series.