PROPERTIES OF THE 2-ELECTRON IONIZATION LADDER AND RELATED GOOD QUANTUM NUMBERS

In recent publications we have presented a general theory for the iden tification and computation of correlated wavefunctions of a particular class of doubly excited states which constitute a two-electron ioniza tion ladder (TEIL) leading smoothly to the so-called Wannier state at E = O. In this work, we examine further the properties of these wavefu nctions for two-electron atoms of S-1 and P-1(0) symmetry, especially as regards their analysis in terms of hydrogenic basis sets and good q uantum numbers. We find that the Herrick-Sinanoglu (K, T) classificati on loses accuracy as we move toward threshold and we show that, when s ingle as well as double excitations are considered, a better quantum n umber for the TEIL is F = N - 1 - K, where N,K are not good numbers an ymore. The extent of the breakdown of the (K, T) representation depend s on the system and on the level of excitation (more serious in negati ve ions and for high lying states). (C) 1993 John Wiley & Sons, Inc.