Core-scattered combination orbits in the M=0 Stark spectrum of helium

Scaled-energy spectroscopy is used to measure the in = 0 Stark recurrence s pectrum of the two spin forms of helium. This case is characterized by much stronger orbit-core interaction than the m = 1 case studied previously. Vi ewed globally as a function of scaled energy epsilon and scaled action (S) over cap clusters of core-scattered recurrences are revealed, emphasizing t heir importance in the Stark spectrum. Data are interpreted using closed-or bit theory. Integrating recurrence peaks over scaled energy allows comparis on between singlet and triplet core scattering, highlighting the link with e + He+ scattering. [S1050-2947(99)04306-1].