Many-body approach to the properties of interacting atoms

Abstract

There is considerable current interest in the theoretical study of intermolecular forces and properties of interacting atoms. During the Eyring symposium, we reported on the application of the Brueckner-Goldstone (BG) many-body perturbation approach [l] to the calculation of the van der Waals (VDW) constant C, , for H-H, H-He, and He-He atoms [2]. The purpose of the present paper is to report the results of our calculation on three-body forces and also the effect of long-range interactions on the hyperfine structure (HFS) of paramagnetic atoms in a diamagnetic buffer gas atmosphere. The former is of considerable interest because a detailed knowledge of three-body dispersion forces is crucial to the quantitative understanding of intermolecular effects in liquids [ 3 ] . The theory of interatomic effects on HFS is of importance in the understanding of the hyperfine pressure shifts observable through optical pumping experiments [4].The VDW constant CAB in the two-body long-range interaction energy expression [5] A ( 2 ) E ( R A B ) = --C24B R-1 L3( 1 ) can be calculated using the expression a( o) being the frequency dependent polarizabilities of the individual atoms. In a similar manner, the leading term of the nonadditive contribution to the interaction of three non-overlapping atoms A , B, and C at separations R,, , RB, , and R,, can be expressed as [6] (3 cos eA cos e B cos ec + 1)

Dipole properties of the metastable 23S state of helium

“…The calculated response functions of a system to time dependent multipole perturbations are also directly utilizable in computing the long range interatomic forces [5] and its effect on other properties of atomic systems such as the hyperfine pressure shift (HPS) of paramagnetic atoms in opticaI pumping experiments [ S ] . In this paper we report on the results of our investigation on the metastable (Is2s: 3S) state of helium and its long range interaction with the ground state of helium.…”