Photoionization of He-like systems below the N=2 threshold

Abstract

The authors have implemented a recently proposed L2-integrable basis method to study photoionization of He-like systems below the n=2 threshold in the framework of a Fano-Feshbach theory. Non-resonant background cross sections and Fano parameters for the (2, n)1P degrees doubly excited states of He and Li+ up to N=5 are calculated. For n>or=3 an anomalous behaviour of the profile parameter q is found in He, which is the result of the existence of interfering, but nevertheless non-overlapping, resonances in the (2, nb) and (2, nc) series. The behaviour of photoionization parameters as a function of the nuclear charge is also discussed.