Is the dipole polarizability of hydrogen iodide accurately known?

A large [21s16p15d7f/11s9p7d3f] basis set consisting of 287 contracted gaussian-type functions yields near-Hartree–Fock non-relativistic values for the mean and the anisotropy of the static dipole polarizability of hydrogen iodide, ᾱ=35.38 and Δα=2.62 e2a02Eh−1. Using a smaller, carefully optimized basis set at the CCSD(T) level of theory, we obtain[ᾱ(R)−ᾱ(Re)]/e2a20E−1h=5.15(R−Re)+1.42(R−Re)2−0.44(R−Re)3−0.57(R−Re)4and[Δα(R)−Δα(Re)]/e2a20E−1h=10.50(R−Re)+3.52(R−Re)2−0.76(R−Re)3−0.75(R−Re)4for the behaviour of the polarizability invariants around the equilibrium bondlength Re=1.60916 Å. Combining our best values, we propose for the ground vibrational state ᾱ=36.52 and Δα=2.94 e2a02Eh−1. Even with the inclusion of relativistic effects the theoretical values are not reconcilable with the available experimental data.