Effects of long-range forces in excitations of simple atomic and molecular systems

Abstract

The influence of long-range forces is examined in excitations between bound states of simple one- and two-center systems. The photoabsorption of light and electron scattering in the near-forward direction are the two excitation processes explored. The one-center system used is an excited state of helium with a nonpenetrating outer electron; the two-center system used consists of two hydrogen atoms separated by a large distance. I consider only nonrelativistic theory and ignore spin. It is found that the long-range forces exert themselves by means of the polarizabilities and induced electric moments in the part of the system which is not excited. As a result, the leading long-range corrections to the transition amplitudes may be expressed in a simple form depending only on these polarizabilities and one-electron operators between hydrogen wave functions.