Ab initio study of the intermolecular potential surface of He–NH3

The intermolecular potential surface for the van der Waals complex He–NH3 is studied by ab initio calculation using fourth-order Møller–Plesset perturbation theory (MP4) with a bond function basis set. The calculation gives a global minimum at R=3.26 Å, θ=89°, φ=60° (in a Jacobi coordinate system) with a well depth of De=32.96 cm−1, along with barriers of 23.09 and 20.86 cm−1 for in-plane rotations at θ=0° and 180°, respectively, and a barrier of 10.45 cm−1 for out-of-plane rotation at θ=89°, φ=0°. The potential energy surface of He–NH3 is compared to those of Ar–NH3 and He–H2O, respectively.