A Molecular Description of Electron Pair Excitation in Atoms

Abstract

It has been thought for some time that the shape, depicted in Fig. 1, of the two-center Coulomb potential in two-electron atoms characterizes much of the atom’s internal motions, particularly for double or “pair” excitations outside an ionic core. The idea is rooted in the familiar Wannier model of threshold double escape (Wannier, 1953; Rau, 1971; Peterkop, 1971). Small total energy E near threshold ensures that electron kinetic energies are small and hence that the escape is strongly dependent on the Interplay of the Interelectronic repulsion 1/R and the electron-ion attraction -Z/r₁-Z/r₂. The breakup is thus characterized by a collinear configuration for the escaping pair along the “Wannier” saddle in the potential, clearly visible in Fig. 1. As the double escape develops and the two electrons and hence the two centers separate, one pictures the saddle as moving about the ion but with its center always located near the ion. This picture excludes the formation of one-electron bound states (single escape) when one or the other of the two-center wells orbits the ion, since the center of the saddle is located halfway between the two electrons at their center of charge.