  Effective Hamiltonians for doubly excited Heliums states based on approximate
O(4) symmetry are revised. New quantum numbers for a 4D Harmonic Oscillator are
assigned to Helium states with both electrons in the n=2 shell. An effective
Hamiltonian operator is constructed and optimzed by means of non-linear
least-square fits to the energy levels of the Helium isoelectronic series. The
results are interpreted in terms of electron correlation and a possible unified
description of two-electron atom intrashell states.
