SHAPE RESONANCE LOCATIONS AND WIDTHS IN ATOMIC PHOTOIONIZATION

The large enhancement of the normalization constants and the rapid var iation of the phase shifts in low-energy continuum wave functions due to screening can lead to a shape resonance in the photoionization tota l cross-sections. We investigate the location of the resonance by usin g the variations of the phase shift and the normalization with respect to the continuum energies and compare the result with an estimate fro m a direct numerical computation of the total cross-sections. We analy ze the shape resonance width by using the Breit-Wigner resonance formu la. We also discuss the shape resonance energy by using the semiclassi cal WKB approximation, considering the shape resonance as a quasi-boun d state.