HIGHLY DOUBLY-EXCITED S-STATES OF THE HELIUM ATOM

We calculate and analyse S-wave resonances of helium up to an energy o f -0.02 au applying the complex rotation technique. Rydberg series con verging to the hydrogenic thresholds of the He+ ion are analysed by qu antum defect theory. For moderately excited inner electrons the series converging to different thresholds begin to overlap resulting in pert urbed Rydberg series. We find that approximate quantum numbers as well as propensity rules governing the decay of the resonances and the per turbation scheme of the Rydberg series prevail. With increasing excita tion of the inner electron however, only series whose states tend to e xtreme interelectronic angles (cos theta) = +/-1 remain regular.