The Wannier two-electron ionisation ladder in many-electron systems: the He 1Psup(o) doubly excited states

A theory is presented for the identification and accurate calculation of a particular class of doubly excited states which lead - as a function of excitation energy - to the 'Wannier state' at the two-electron ionisation threshold of any atom in any symmetry. An application to the He 1Psup(o) Wannier two-electron ionisation ladder is considered. Conditional probability density plots of these states are presented which show how the localisation around (r1)=(r2) and (theta12)=π increases as a function of the principle quantum number n. The energies are fitted to an effective Rydberg-like formula Esub(n)=-(Z - σ)2/ (n+μ)2 with σ=0.16244 and μ=0.1595. (author)