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 (upsilon > 20) of the singly excited O-g(-) state predissociate into the 3(2)P(3/2) + 3(2)S(1/2)(F-g=1) 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.