Interaction potentials for diffraction of a He atom by a NaCl(001) surface

There exist two quite different sets of experimental results for the He-NaCl(001) interaction potential, inferred from bound-state resonance measurements of associated ⁴He-NaCl(001) bound-state energies E_n: Frankl's group has found a lowest bound-state energy E₀ ≈ −4.1 meV, whereas Benedek's group has found evidence of a deeper interaction potential well, with E₀≈ −7.2 meV. Furthermore, there are strong physical arguments for the existence of the deeper well. In the present paper, interaction potentials, based on empirical pairwise He-Na⁺ and He-Cl⁻ interactions, for diffraction of a He atom by a NaCl(001) surface are considered. Comparisons of close-coupling diffraction calculations with experimental data of Frankl's group are made, and values of the empirical parameters are inferred. On the basis of these comparisons, it is concluded that the lowest bound state proposed by Benedek's group is absent, and that the correct bound-state energies are those proposed by Frankl's group.