Observation of ultracold ground-state potassium molecules

Ultracold potassium molecules are produced in the X (1)Sigma(g)(+) electron ic ground state by photoassociation in a magneto-optical trap. They are det ected sensitively and selectively by use of two-color resonant ionization, followed by time-of-flight mass spectroscopy. We observe deeply bound molec ules with nu congruent to 36, at a temperature of about 300 mu K. Presently about 1000 molecules/sec are produced, and much higher production rates sh ould be attainable in the future.