Modeling Photoassociative Spectra of Ultracold NaK + K.

A model for photoassociation of ultracold atoms and molecules is presented and applied to the case of 39 K and 23 Na 39 K 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 X 1 Σ + ground state toward the metastable b 3 Π lowest excited state of 23 Na 39 K, allowing us to neglect any other excitation, which could hinder the photoassociation detection. The energy level structure of the long-range 39 K··· 23 Na 39 K excited super-dimer is computed in the space-fixed frame by solving coupled-channel equations, involving the coupling between the 23 Na 39 K 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.