Hyperfine Pressure Shift and van der Waals Interactions. I. Hydrogen-Helium System

Abstract

The origin of the hyperfine pressure shift (HPS) for hydrogen atoms in a helium atmosphere has been analyzed quantitatively. The theory is discussed in terms of three distinct regions of interaction. Calculations are carried out explicitly for the short-range and long-range regions, and the importance of the intermediate region is investigated. At short range, the Pauli distortion effect is treated through an orthogonalization procedure, and a variation-perturbation approach is utilized to consider the long-range van der Waals interaction. Our theoretical result for the HPS is 1.9 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$/mm Hg as compared with the experimental value of 3.7 \ifmmode\pm\else\textpm\fi{} 0.7 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}9}$/mm Hg. The major sources for the discrepancy between these results appear to be neglect of correlation effects and uncertainties with respect to the intermediate-range contribution.