Ultracold $O_2$+$O_2$ collisions in a magnetic field: on the role of the potential energy surface

TL;DR

This study investigates ultracold oxygen molecule collisions in a magnetic field using a recent ab initio potential energy surface, revealing significant resonance structures and sensitivity to short-range interactions, with implications for understanding molecule-molecule interactions.

Contribution

It provides the first detailed analysis of ultracold O₂+O₂ collisions using an ab initio PES, highlighting the impact of the PES on resonance behavior and scattering properties.

Findings

Presence of broad Feshbach resonances in low-field-seeking states.

Strong sensitivity of scattering to the potential energy surface.

Large background scattering length influences resonance structure.

Abstract

The collision dynamics of $^{17}O_2(^3\Sigma_g^-) +^{17}O_2(^3\Sigma_g^-)$ 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 {\em 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 [New J. Phys {\bf 11}, 055021 (2009)]. In contrast to the results using the older PES, magnetic field dependence of the low-field-seeking state in the ultracold regime is characterized by quite a large background scattering length, $a_{bg}$, and, in addition, cross sections exhibit broad and 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 wave function is enhanced by the large $a_{bg}$. This strong sensitivity to the short range of the {\em 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 towards large scattering lengths, could be also characteristic of other anisotropic molecule-molecule systems.