Long-lived resonant states in Planetary atoms

We report on a class of long-lived resonant states of doubly excited twoelectron atoms which exhibit distinct angular and radial electron correlation. The states are characterized by a highly polarized inner electron located near the axis between the nucleus and a dynamically localized outer electron. Classical mechanics studies prove the stability of the corresponding classical motion and allow for EBK-quantization to obtain semiclassical energies. The resonance states are treated further within the framework of a single channel adiabatic approximation. The adiabatic energies as well as the semiclassical results are in good agreement with resonance energies obtained by highly accurate solutions of the full three-body Schrodinger equation. Approximate quantum numbers derived from the semiclassical and from the adiabatic approach explain the nodal structures of the full quantum wavefunctions. The decay widths of the resonances turn out to be extremely small