Single-color photoassociative ionization of ultracold sodium: The region from 0 to 5 GHz - art. no. 013408

We have measured the rate of production of Na-2(+) ions in collisions of ul tracold Na atoms held in a magneto-optical trap (MOT) as a function of prob e laser detuning using a single-color probe beam. The ion rate is measured with the atoms mainly in the 3S(f = 2) level ("bright MOT'') or the 3S(f = 1) level ("dark MOT''). Usings recent experimental information about the do ubly excited autoionizing states of Na-2, we find that the large structures in the first 5 GHz red of the atomic transition frequency are due to a dou bly resonant excitation process with levels in the O-g(-) potential (asympt otically connected to 3S(1/2) + 3P(3/2)) as the intermediate states, and le vels in the 0(u)(-) and 1(u) potentials (asymptotically connected to 3P(3/2 ) + 3P(3/2)) as the final autoionizing states. We can account for nearly al l of the observed structure in this region of the spectra for both the brig ht and dark MOT.