Hyperfine Pressure Shift and van der Waals Interaction. II. Nitrogen-Helium System

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Abstract
In continuation of a series of investigations of hyperfine pressure shifts (HPS) in interacting atoms, an investigation of the long-range interaction of nitrogen atoms in a helium atmosphere is reported. The procedure requires wave functions perturbed to first order in the van der Waals and nuclear hyperfine Hamiltonians, respectively. The van der Waals perturbed wave function is obtained through a variational procedure described previously for the H-He system. The first-order hyperfine wave function is a moment-perturbed (MP) function used in an earlier study of the short-range N-He interaction. The theoretical result for the longrange contribution to HPS is 0.22 cps/mm Hg to be combined with a contribution from shortrange of 0.91 cps/mm Hg, as compared with a total experimental HPS of 0.27±0.07 cps/mm Hg. Various factors which might contribute to the difference between theory and experiment are discussed. In particular, the role of correlation at short range is stressed.