In recent publications we have presented a general theory for the identification and computation of correlated wavefunctions of a particular class of doubly excited states which constitute a two-electron ionization ladder (TEIL) leading smoothly to the so-called Wannier state at E = 0. In this work, we examine further the properties of these wavefunctions for two-electron atoms of 1S and 1Po symmetry, especially as regards their analysis in terms of hydrogenic basis sets and good quantum numbers. We find that the Herrick–Sinanoglu (K, T) classification loses accuracy as we move toward threshold and we show that, when single as well as double excitations are considered, a better quantum number for the TEIL is F = N - 1 - K, where N,K are not good numbers anymore. The extent of the breakdown of the (K, T) representation depends on the system and on the level of excitation (more serious in negative ions and for high lying states). © 1993 John Wiley & Sons, Inc.
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