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

Abstract

We report new high resolution molecular beam experiments aimed at characterizing the intermolecular interaction in the NH(3)-Ng (Ng = He, Ne, Ar, Kr, Xe) weakly bound complexes. Integral cross section data are obtained over a sufficiently wide velocity range and with rotationally hot NH(3) molecules to produce (except for the NH(3)-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 component 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.

Scattering of NH3 and ND3 with rare gas atoms at low collision energy

“…These values can be compared to those obtained by Pirani et al from high resolution molecular beam experiments in which the elastic cross sections for NH 3 -Rg scattering were measured. 21 There is good agreement with the present values for all parameters, except for NH 3 -Xe where the discrepancy in the value of ϵ m is somewhat larger. …”

“…[10][11][12][13][14][15] Although the literature is less extensive regarding the other NH 3 -Rg complexes, these systems have also been studied experimentally in spectroscopic [16][17][18][19] or molecular beam experiments. 20,21 Recent advances on the manipulation and control of molecular beams have renewed interest in these systems. Measurements of rotationally inelastic, quantumstate resolved, differential cross sections were realized using a hexapole-focused beam of ND 3 molecules colliding with various rare gases (Rg's) or molecular hydrogen.…”

Potential energy surface and bound states of the NH3–Ar and ND3–Ar complexes

“…The band origins E 0 and the rotational and distortion constants B and D are reported in Table IV for these states and compared to the available experimental data. The energies E 0 are given with respect to the lowest rovibrational state of para NH 3 -Ar ( 1 1 ) 1 and l 1 1 are strongly mixed by the Coriolis interaction, and it was found better to fit the energies of both states simultaneously. 9 In order to compare with the experimental data, the values reported in Table IV are As in the case of the ortho states, we find excellent agreement with the experimental data for the energies E 0 , TABLE III.…”

“…The interaction of ammonia with noble gases (NG) has been the subject of a large number of studies motivated mainly by the understanding of weak interactions 1 as well as by the importance of rotational energy transfer in NH 3 -NG collisions in the modelling of various astrophysical and atmospherical environments. 2 Moreover, the possibility of producing cold and ultracold NH 3 molecules either by buffer gas cooling or by sympathetic cooling with noble gas atoms has been examined.…”

“…The most recent PES was obtained by Schmuttenmaer et al 25 by fitting the spectroscopic data, which provided a detailed understanding of the spectrum of the complex. Finally, geometry optimization calculations were performed recently by Bistoni et al 26 using the coupled cluster method, in relation with molecular beam experiments probing the isotropic part of the PES, 1 with good agreement between theory and experiment.…”