Photoassociative ionization of heteronuclear molecules in a novel two-species magneto-optical trap

We describe the experimental observation of ultracold NaCs+ molecular forma tion in a novel two-species magneto-optical trap. We interpret our observat ions in terms of a photoassociative ionization pathway similar to that obse rved in a sodium trap: Na + Cs + (h) over bar omega(Na) + (h) over bar omeg a(Cs) --> NaCs+ + e(-). We have directly measured the: NaCs+ production rat e as a function of the excitation laser frequency and intensity elucidating the role of ground-state hyperfine levels. We have observed resonance stru ctures in the frequency-dependent ion rate which we associate with the mole cular character of the process, [S0031-9007(98)08234-9].