Modeling Photoassociative Spectra of Ultracold NaK plus K

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