Modeling Photoassociative Spectra of Ultracold NaK + K

A model for photoassociation of ultracold atoms and molecules is presented and applied to the case of ³⁹K and ²³Na³⁹K bosonic particles. The model relies on the assumption that photoassociation is dominated by long-range atom-molecule interactions well outside the chemical bond region. The frequency of the photoassociation laser is chosen close to a bound-bound rovibronic transition from the X¹Σ⁺ ground state toward the metastable b³Π lowest excited state of ²³Na³⁹K, allowing us to neglect any other excitation, which could hinder the photoassociation detection. The energy level structure of the long-range ³⁹K···²³Na³⁹K excited super-dimer is computed in the space-fixed frame by solving coupled-channel equations, involving the coupling between the ²³Na³⁹K internal rotation and the mechanical rotation of the super-dimer complex. A quite rich structure is obtained, and the corresponding photoassociation rates are presented. Other possible photoassociation transitions are discussed in the context of the proposed model.