Molecular-beam study of the ammonia–noble gas systems: Characterization of the isotropic interaction and insights into the nature of the intermolecular potential

We report new high resolution molecular beam experiments aimed at characterizing the intermolecu- lar interaction in the NH3–Ng (Ng = He, Ne, Ar, Kr, Xe) weakly bound complexes. Integral cross sec- tion data are obtained over a sufficiently wide velocity range and with rotationally hot NH3 molecules to produce (except for the NH3–He case) a well resolved “glory” quantum interference pattern. Data analysis, carried out by employing a recently proposed potential model, allows unique information on the absolute scale of the intermolecular interaction to be obtained both at long range and at the equilibrium distance. An extensive and internally consistent comparison with the behavior of the corresponding Kr–Ng systems is exploited in order to identify those cases where an interaction com- ponent due to charge transfer effects provides an appreciable intermolecular bond stabilization that is clearly distinct from and must be added to the standard van der Waals plus induction picture. The results of the present investigation extend the phenomenology of perturbative charge transfer effects in gas phase complexes involving hydrogenated molecules.