Semiclassical cycle expansion for the helium atom

The authors analyse the classical dynamics of near-collinear electron configurations in helium. The dynamics turns out to be fully chaotic. An application of periodic orbit quantization techniques yields the energy of doubly excited states with high accuracy. The analysis shows that near-collinear intra-shell resonances are associated with an asymmetric stretch like motion of the electron pair rather than the symmetric stretch motion along the Wannier ridge.