Many-Body Approach to the Hyperfine Pressure Shift in Optical-Pumping Experiments

Abstract
The formulation of the van der Waals (VDW) interaction between atoms in terms of frequency-dependent polarizabilities is extended to the problem of the long-range contribution to the hyperfine pressure shift in optical-pumping experiments. The requisite perturbed-energy expression for the present problem involves two orders of VDW interaction and one order of magnetic hyperfine interaction. This expression is recast in terms of integrals involving requisite frequency-dependent response functions which are evaluated using the Brueckner-Goldstone many-body technique applied earlier to VDW energy calculations. Specific applications are made to H-He and H-Ne systems. The fractional shift ΔAA0 of the hyperfine constant is expressed in the form of DHXR6, where R (a.u.) is the separation between H and X atoms. The values we obtain for DHX are 13.34 and 26.13 for X=He and Ne, respectively. This analysis removes one of the important uncertainties in hyperfine-pressure-shift calculations, namely, the influence of correlation effects on the long-range part of ΔAA0.