Abstract

Indirect spin-spin interactions between nuclei bound in a molecule are well known in nuclear magnetic resonance, but such interactions between unbound atoms are less well studied and are often assumed to be zero. We present a precision calculation of this interaction between ¹²⁹Xe and ³He nuclei in a gas. Relativistic, state-of-the-art electronic structure theory is used to compute the scalar coupling constant \(J(R)\) and the interatomic potential energy function \(V(R)\) as functions of the Xe-He internuclear distance \(R\). Using virial expansion we find the nuclear spin enhancement factor κ = −0.0105 ± 0.0015, in excellent agreement with recent experiments. This interaction is particularly important for precision measurements using nuclear spin comagnetometers.