“…It might, for example, be expected that HF, having the largest B 0 value, will on solvation exhibit the smallest reduction in rotational constant of the three molecules. Although several potential energy surfaces for He−HX (X = F, Cl, Br) already exist in the literature, − to make a more consistent and even-handed comparison, ab initio PESs for all three complexes are computed and fitted to the same functional form. We find that (i) it is not only the size of the anisotropy that matters but also its symmetry; that is, which Legendre polynomials contribute to the angular anisotropy; and (ii) the bosonic symmetry of the solvent requires that all of the He atoms couple identically to the molecule.…”