Laser cooling and the highest bound states of the Na di-atom system.

Using a multi-channel bound-state method we predict the highest bound states of the 23 Na di-atom system, closely related to the collisional behavior of ultra-cold atoms. The results agree well with a model where the hyperfine interaction is treated in first order perturbation theory, except for the triplet level closest to the continuum, which we predict to be very weakly bound. This level is responsible for the large, positive scattering length of the m f = \Sigmaf states of the lower hyperfine manifold. Its experimental observation would confirm our prediction of a stable Bose condensate. Pacs number(s): 32.80.Pj,42.50.Vk Typeset using REVT E X Collisions between cold atoms play an important role in the rapidly developing field of laser cooling experiments. They are interesting as a largely unexplored kind of collisions in a new temperature regime [1] and are crucial in determining fundamental limits on the accuracy in precision experiments like the cesium atomic frequency stand..