Abstract

The effects of electron correlation in atomic and molecular systems are perhaps most pronounced in negative ions. No long-range Coulomb field is present to bind an additional electron to a parent state of a neutral atom. The stability of a negative ion state is thus usually attributed to one of two alternative mechanisms, both of which invoke electron correlation phenomena: i) polarization of the parent atom provides an attractive potential in which an electron can be weakly bound; ii) two electrons orbit a singly-charged positive ion in a highly correlated fashion, so that each electron is effectively subject to the Coulomb potential of a fractional charge. These correspond respectively to motions in the valleys and upon the ridge of a hyperspherical potential surface. Both mechanisms seem capable of generating the long series of resonances converging on the parent ionization limit, which have been observed in most negative ion systems.¹

© 1986 Optical Society of America