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We study the role of pairwise long-range interactions in the formation of van der Waals molecules through direct three-body recombination processes A + B + B → AB + B, based on a classical trajectory method in hyperspherical coordinates developed in our earlier works [J. Pérez-Ríos et al., J. Chem. Phys. 140, 044307 (2014); M. Mirahmadi and J. Pérez-Ríos, J. Chem. Phys. 154, 034305 (2021)]. In particular, we find the effective long-range potential in hyperspherical coordinates with an exact expression in terms of dispersion coefficients of pairwise potentials. Exploiting this relation, we derive a classical threshold law for the total cross section and the three-body recombination rate yielding an analytical expression for the three-body recombination rate as a function of the pairwise long-range coefficients of the involved partners. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The collision dynamics of 17O2(3Σg-)+17O2(3Σg-) in the presence of a magnetic field is studied within the close-coupling formalism in the range between 10 nK and 50 mK. A recent global ab initio potential energy surface (PES) is employed and its effect on the dynamics is analyzed and compared with previous calculations where an experimentally derived PES was used [T. V. Tscherbul et al., New J. Phys 134, 055021 (2009)]. Compared to the results using the older PES, magnetic-field dependence of the low-field-seeking state in the ultracold regime is characterized by a very large background scattering length, abg, and cross sections exhibit broader and more pronounced Feshbach resonances. The marked resonance structure is somewhat surprising considering the influence of inelastic scattering but it can be explained by resorting to the analytical van der Waals theory, where the short-range amplitude of the entrance channel wavefunction is enhanced by the large abg. This strong sensitivity to the short range of the ab initio PES persists up to relatively high energies (10 mK). After this study and despite quantitative predictions are very difficult, it can be concluded that the ratio between elastic and spin relaxation scattering is generally small, except for magnetic fields which are either low or close to an asymmetric Fano-type resonance. Some general trends found here, such as a large density of quasibound states and a propensity toward large scattering lengths, could be also characteristic of other anisotropic molecule-molecule systems. [ABSTRACT FROM AUTHOR]

An optimal procedure for obtaining spherically averaged potentials for the interaction between two linear centrosymmetric molecules (Koide and Kihara, Chem Phys 1974, 5, 34) is extended here for the calculation of the leading anisotropy term of the interaction. It is found that by computing the potential just at nine specific relative orientations of the monomers, the main anisotropy term of the spherical harmonic expansion can be calculated exactly provided that the expansion does not involve more than the first 14 terms. The approach also serves to investigate, in an affordable manner, the dependence of the interaction potential on the intramolecular degrees of freedom, and, in this way, to go beyond the commonly used rigid rotor approximation. Application has been performed for the [O(Σ)] dimer by means of high-level ab initio calculations (RCCSD(T) method), and results are compared with a previous accurate rigid rotor potential energy surface. It is found that both the present isotropic and main anisotropy terms are very reliable and that the effect of the corrected vibrationally averaged potential is of about 1%. In addition, the dependence of the intermolecular potentials with the intramolecular vibrational modes is analyzed for the different geometries studied. The treatment can be quite useful in a realistic description of the main features of intermolecular interactions in more complex systems. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]