Long range intermolecular forces in triatomic systems: connecting the atom–diatom and atom–atom–atom representations

Abstract

The long-range forces that act between three atoms are analysed in both atom-diatom and atomatom-atom representations. Expressions for atom-diatom dispersion coefficients are obtained in terms of 3-body nonadditive coefficients. The anisotropy of atom-diatom C6 dispersion coefficients arises primarily from nonadditive triple-dipole and quadruple-dipole forces, while pairwise-additive forces and nonadditive triple-dipole and dipole-dipole-quadrupole forces contribute significantly to atom-diatom C8 coefficients. The resulting expressions are applied to dispersion coefficients for Li + Li2 (triplet) and recommendations are made for the best way to obtain global triatomic potentials that dissociate correctly both to three separated atoms and to an atom and a diatomic molecule.

Interactions and dynamics in Li+Li2 ultracold collisions

“…50 However, for Li+ Li 2 the nonadditive term is so large that the potential minimum for the trimer occurs at a distance that is high on the repulsive wall for the dimer. Because of this, Eq.…”

“…The need to include the nonadditive term has been described in detail in Ref. 50. In particular, the sum of pair potentials gives an isotropic atom-diatom C 6 coefficient, whereas in reality there are important anisotropic terms.…”

“…For the pairwise potentials V dimer ͑r͒, we used the Li 2 RKR potential of Linton et al, 47 which extrapolates to a three-term dispersion expression with coefficients C 6 , C 8 , and C 10 as given by Yan et al 46 The nonadditive potential was constructed as described in Ref. 50 64 The long-range form V LR ͑r͒ is designed to be valid when any of the atom-atom distances is large. The short-range ͑IMLS͒ and long-range potentials were joined using the switching function …”

Formation of molecular oxygen in ultracoldO+OHcollisions

“…As r OH increases, the diatomic mixing decreases and α 1 → 1 and α 2 → 1. The dependence of the long-range coefficients for atom -diatom interactions on the diatomic separation has also been noted and investigated in recent work on the Li + Li 2 and Na + Na 2 systems [75,76]. For the atommolecule reduced mass we used µ = 15023.74 au.…”

Molecular collisions in ultracold atomic gases

“…Inspired by the recent progress in experimental techniques for producing and studying ultracold molecules, we have collaborated with Jean-Michel Launay and coworkers at the University of Rennes to produce a series of theoretical studies [35,46,47,48,49,50,51,52] on interactions and collisions between spin-polarized alkalimetal atoms and molecules. In particular, ultra-lowenergy collisions were studied for Na + Na 2 [46,48], Li + Li 2 (isotopically homonuclear [35,49] and heteronuclear [50]), and K + K 2 [51].…”