Ultracold and quantum degenerate mixtures of two or more atomic species open up many new research avenues, including the formation of ultracold heteronuclear ground-state molecules possessing a permanent electric dipole moment. The anisotropic, long range dipole-dipole interactions between such molecules offer many potential applications, including novel schemes for quantum information processing and simulation. Our goal is to create ultracold ground-state RbCs molecules using magneto-association on a Feshbach resonance followed by optical transfer to the rovibronic ground state. Here we present a detailed study of the Feshbach spectrum for and ultracold atomic mixture of Rb and Cs. We report five interspecies s-wave resonances for 87Rb-Cs in the magnetic field range up to 1100 G. We present a thorough characterisation of the interspecies scattering length dependence for 85Rb-Cs for magnetic fields up to 700 G and observe nine Feshbach resonances. We also examine the case of a single species 85Rb gas, where we report 16 experimentally observed intraspecies resonances. We demonstrate that all the resonances are in good agreement with coupled-channel calculations.
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