Hyperfine pressure shift and Van der Waals interactions. I. Hydrogen-Helium System

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 × 10-9/mm Hg as compared with the experimental value of 3.7 ± 0.7 × 10-9/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. © 1968 The American Physical Society.