An improved potential energy surface for the degenerate rearrangement of (HF)2

We report a new potential energy surface for the (HF)2 van der Waals molecule and quantum mechanical nine-dimensional eigenvalue calculations of vibrational energy levels on this surface. The new surface has been adjusted to give an accurate tunneling splitting but is otherwise based on the SQSBDE potential energy surface of Quack and Suhm. We obtain a ground-state dissociation energy of 1076.1 cm−1 and a ground-state tunneling splitting of 0.65 cm−1, in good agreement with the experimental values of 1062 cm−1 and 0.659 cm−1, respectively.