Rydberg and autoionizing triplet states in Helium up to the NÂ =Â 5 threshold

Energy levels of highly excited bound Rydberg states, the position and widths of autoionizing states, and oscillator strengths are calculated for He 3S, 3Pe, 3Po, 3De and 3Do symmetries up to the N = 5 He+ excitation threshold. The calculations are performed with the K-matrix B-spline method with maximum orbital angular momentum ℓmax = 8. Reliable doubly excited-state parameters up to the n = 20 multiplet below each ionization threshold are presented. One thousand and six hundred newly identified bound and metastable states, seven times those available in literature, fill many gaps, reveal a dozen intruder states, and allow new speculations on propensity rules and radiative decays of triplet Rydberg states.