Triatomic Photoassociation in an Ultracold Atom–Molecule Collision

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2023-01, Vol.127 (1), p.18-28
• Main Authors: Elkamshishy, Ahmed A., Greene, Chris H.
• Format: Article
• Language: English
• Subjects: A: Structure, Spectroscopy, and Reactivity of Molecules and Clusters
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.2c04727

Ultracold collisions of neutral atoms and molecules have been of great interest since experimental advances enabled the cooling and trapping of such species. This study develops a simplified theoretical treatment of a low-energy collision between an alkali atom and a diatomic molecule accompanied by absorption of a photon from an external electromagnetic field. The long-range interaction between the two species is treated, including the atomic spin–orbit interaction. The long-range potential energy curves for the triatomic complex are calculated in realistic detail, while effects of the short-range behavior are mimicked by applying different boundary conditions at the van der Waals length. For neutral colliding species, the leading interaction term is the dipole–dipole interaction. In the case of nonpolar dimers like Cs2, the second leading term is the quadrupole–quadrupole interaction. However, there is also a strong dipole–quadrupole interaction for dimers with a large permanent dipole moment such as NaCs, making the dipole–quadrupole interaction the second leading term for an atom colliding with a polar dimer. Our applications of the simplified treatment show a higher density of trimer states for a polar dimer compared to the case of a nonpolar dimer like Cs2. This is a consequence of the strong quadrupole–dipole coupling between the atom and the dimer dipole moment.