On the formation of van der Waals complexes through three-body recombination

Abstract

In this work, we show that van der Waals molecules X-RG (where RG is the rare gas atom) may be created through direct three-body recombination collisions, i.e., X + RG + RG → X-RG + RG. In particular, the three-body recombination rate at temperatures relevant for buffer gas cell experiments is calculated via a classical trajectory method in hyperspherical coordinates [Pérez-Ríos et al., J. Chem. Phys. 140, 044307 ( 2014)]. As a result, it is found that the formation of van der Waals molecules in buffer gas cells (1 K ≲ T ≲ 10 K) is dominated by the long-range tail (distances larger than the LeRoy radius) of the X-RG interaction. For higher temperatures, the short-range region of the potential becomes more significant. Moreover, we notice that the rate of formation of van der Walls molecules is of the same order of the magnitude independent of the chemical properties of X. As a consequence, almost any X-RG molecule may be created and observed in a buffer gas cell under proper conditions.

Ozone formation in ternary collisions: Theory and experiment reconciled

“…The present approach is based on a classical trajectory (CT) method in hyperspherical coordinates, which has shown efficiency for reactive collisions of three neutral atoms [11][12][13]29] as well as for ion-neutral-neutral ternary recombination processes [30][31][32]. The method is adapted to the present problem representing the O 2 molecule as a super-atom.…”

“…Figure 5 gives the rate coefficients for the formation of all three possible products of the reaction, O 3 , ArO 2 , and ArO. The figure demonstrates two distinct characteristics: First, at low collision energies (E c 130 K) [13,29], ArO 2 is formed more quickly than ArO, which is formed more quickly than O 3 (assuming equal densities of Ar, O, and O 2 ). The result is explained by the fact that the attractive potential of the Ar-O 2 system decays slower than that of Ar-O, so that it has a larger density of available vibrational states to be formed (a larger phasespace volume in the classical formulation of the problem).…”

“…The novelty of the present work is that it aims at obtaining the rate coefficient considering the ternary collision O 2 + O + M without splitting the process into two steps. The present theoretical approach combines an ab initio potential energy surfaces (PES) of the ArO 3 system, obtained in this study, and the classical-trajectory method in hyperspherical coordinates developed previously by two of us et al [11][12][13].…”

Classical threshold law for the formation of van der Waals molecules

“…[34][35][36][37][38] In Ref. [39], we considered the formation of atom-rare gas vdW molecules via a direct three-body recombination mechanism at temperatures relevant for buffer gas cell experiments. As a result, we found that almost any atom a) Electronic mail: mirahmadi@fhi-berlin.mpg.de b) Electronic mail: jperezri@fhi-berlin.mpg.de in a helium buffer gas will evolve into a vdW molecule.…”

“…Fueled by those results, our goal in the present work is to present a comprehensive study of A + B + B → AB + B reactions and derive a classical threshold law for the formation of vdW molecules in cold environments. To investigate this problem, we use a classical approach in hyperspherical coordinates, which has previously been used to consider the three-body recombination of three neutral atoms, 33,39,40 as well as ion-neutral-neutral threebody recombination processes. 36,37,41 In order to derive a threshold law, we have obtained an effective long-range potential in hyperspherical coordinates.…”