Precise determination of $^6$Li cold collision parameters by   radio-frequency spectroscopy on weakly bound molecules
  We employ radio-frequency spectroscopy on weakly bound $^6$Li$_2$ molecules to precisely determine the molecular binding energies and the energy splittings between molecular states for different magnetic fields. These measurements allow us to extract the interaction parameters of ultracold $^6$Li atoms based on a multi-channel quantum scattering model. We determine the singlet and triplet scattering lengths to be $a_s=45.167(8)a_0$ and $a_t=-2140(18)a_0$ (1 $a_0$ = 0.0529177 nm), and the positions of the broad Feshbach resonances in the energetically lowest three $s-$wave scattering channels to be 83.41(15) mT, 69.04(5) mT, and 81.12(10) mT. 
M. Bartenstein, A. Altmeyer, S. Riedl, R. Geursen, S. Jochim, C. Chin,   J. Hecker Denschlag, R. Grimm, A. Simoni, E. Tiesin...