  We report on measurements of the binding energies of several weakly bound
vibrational states of the paramagnetic $^{174}$Yb$^{6}$Li molecule in the
electronic ground state using two-photon spectroscopy in an ultracold atomic
mixture confined in an optical dipole trap. We theoretically analyze the
experimental spectrum to obtain an accurate description of the long-range
potential of the ground state molecule. Based on the measured binding energies,
we arrive at an improved value of the interspecies $s$-wave scattering length
$a_{s0}=30$ $a_0$. Employing coherent two-photon spectroscopy we also observe
the creation of ''dark'' atom-molecule superposition states in the
heteronuclear Yb-Li system. This work is an important step towards the
efficient production of ultracold YbLi molecules via association from an
ultracold atomic mixture.

Atomic Physics