Helium structures around SF 5 + and SF 6 + : novel intermolecular potential and mass spectrometry experiments.

Helium clusters around the recently experimentally observed sulphur hexafluoride SF6 + and sulphur pentafluoride SF5 + ions are investigated using a combined experimental and theoretical effort. Mass spectrometry ion yields are obtained and the energetics and structure of the corresponding He N -SF6 + and He N -SF5 + clusters are analyzed using path integral molecular dynamics calculations as a function of N , the number of He atoms, employing a new intermolecular potential describing the interaction between the dopant and the surrounding helium. The new force field is optimized on benchmark potential energy ab initio calculations and represented by improved Lennard-Jonnes analytical expressions. This procedure improves the previous potentials employed in similar simulations for neutral SF6 attached to helium nanodroplets. The theoretical analysis explains the characteristic features observed in the experimental ion yields which suggest the existence of stable configurations at specific sizes.