Long-Range Predissociation in Two-Color Photoassociation of Ultracold Na Atoms

We report two-color photoassociative ionization of sodium in a magneto-optical trap. The experimental results yield information on both singly and doubly excited states. We find that the highest bound vibrational levels ( $v>\mathrm{}20\mathrm{}$) of the singly excited $0_g^{-}$ state predissociate into the $3^2{P}_{3/2}{+3\mathrm{}}^2{S}_{1/2}(F_g=1\mathrm{})$ dissociation continuum due to avoided crossings of the hyperfine components of this potential with other molecular symmetries. Based on symmetry and energy consideration we argue that a doubly excited $1_u$ state remains autoionizing even when excited only a few GHz above the dissociation continuum.