Formation of fermionic molecules via interisotope Feshbach resonances

We perform an analysis of recent experimental measurements and improve the lithium interaction potentials. For {sup 6}Li a consistent description can be given. We discuss theoretical uncertainties for the position of the wide {sup 6}Li Feshbach resonance, and we present an analytic scattering model for this resonance, based on the inclusion of a field-dependent virtual open-channel state. We predict new Feshbach resonances for the {sup 6}Li-{sup 7}Li system, and their importance for different types of crossover superfluidity models is discussed.