  We report on the creation and characterization of heteronuclear KRb Feshbach
molecules in an optical dipole trap. Starting from an ultracold gas mixture of
K-40 and Rb-87 atoms, we create as many as 25,000 molecules at 300 nK by rf
association. Optimizing the association process, we achieve a conversion
efficiency of 25%. We measure the temperature dependence of the rf association
process and find good agreement with a phenomenological model that has
previously been applied to Feshbach molecule creation by slow magnetic-field
sweeps. We also present a measurement of the binding energy of the
heteronuclear molecules in the vicinity of the Feshbach resonance and provide
evidence for Feshbach molecules as deeply bound as 26 MHz.
