Hyperfine, rotational and Zeeman structure of the lowest vibrational   levels of the $^{87}$Rb$_2$ $\tripletex$ state
  We present the results of an experimental and theoretical study of the electronically excited $\tripletex$ state of $^{87}$Rb$_2$ molecules. The vibrational energies are measured for deeply bound states from the bottom up to $v'=15$ using laser spectroscopy of ultracold Rb$_2$ Feshbach molecules. The spectrum of each vibrational state is dominated by a 47\,GHz splitting into a $\cog$ and $\clg$ component caused mainly by a strong second order spin-orbit interaction. Our spectroscopy fully resolves the rotational, hyperfine, and Zeeman structure of the spectrum. We are able to describe to first order this structure using a simplified effective Hamiltonian. 
T. Takekoshi, C. Strauss, F. Lang, J. Hecker Denschlag, M. Lysebo, L.   Veseth
physics.atom-ph quant-ph