MECHANISM OF THE ENHANCEMENT OF SOME HIGH-LYING RESONANCE SERIES IN THE PHOTOIONIZATION SPECTRA OF EXCITED HELIUM

The hyperspherical close-coupling method is used to compare the detail ed structures in the photoionization spectra of He(1 1S) and He (2 1S ) between the He+ (n=4) and He+ (n=6) thresholds; both the total photo ionization cross section and the partial cross sections for the produc tion of He+ (n) are studied. Some doubly excited resonance series of e xcited angular modes that are either weak or unobservable in the groun d-state spectrum are greatly enhanced in the metastable-state spectrum . This corroborates that previously derived propensity rules do not ap ply, in fact, to the photoionization of He(2 1S). The dependence of t he propensity rules on the initial state is interpreted in terms of th e correlation patterns of its wave function in the region of the hyper radius that contributes dominantly to the photoionization cross sectio n. This interpretation suggests a generality of the enhancement of som e resonance series in excited-state spectra. Some overlapping resonanc es that are overlooked in the literature are uncovered and analyzed by using the Gailitis-average procedure.