A new Bohr-Rydberg spectrum of two-electron states

Recently observed states in He - in which two electrons reach high levels of excitation are shown to fit a Rydberg sequence of bound-state energy levels in a six-dimensional Coulomb potential (1/R). Thereby, these states provide conclusive evidence for a new class of quantised energy levels residing at the 'Wannier saddle point' of the two-electron system. In the vicinity of this saddle point of the potential surface, the system reduces to that of a single particle in an attractive Coulomb potential in the six-dimensional hyperspherical radius R=(r 1 2 +r 2 2 ) 1 2/. Energy positions, angular momentum aspects and intensity ratios of the observed states are all in conformity with this picture.