Feshbach resonances in Na-23 + K-39 mixtures and refined molecular potentials for the NaK molecule

We present a detailed study of interspecies Feshbach resonances of the bosonic Na-23 + K-39 mixture for magnetic fields up to 750 G in various collision channels. A total of 14 Feshbach resonances are reported, as well as four zero crossings of the scattering length and three inelastic two-body loss features. We use the observed magnetic-field locations of the resonant features together with the known data on Na-23 + K-40 to refine the singlet and triplet ground-state potentials of NaK and achieve a consistent description of Feshbach resonances for both the Bose-Bose mixture of Na-23 + K-39 and the Bose-Fermi mixture of Na-23 + K-40. We also discuss the influence of the interplay between inelastic two-body and three-body processes on the observation of a Feshbach resonance.