  We report on photoassociation spectroscopy probing the $c^3\Sigma_{1}^+$
potential of the bi-alkali NaCs molecule, identifying eleven vibrational lines
between $v' = 0$ and $v' = 25$ of the excited $c^3\Sigma_{1}^+$ potential, and
resolving their rotational and hyperfine structure. The observed lines are
assigned by fitting to an effective Hamiltonian model of the excited state
structure with rotational and hyperfine constants as free parameters. We
discuss unexpected broadening of select vibrational lines, and its possible
link to strong spin-orbit coupling of the $c^3\Sigma_{1}^+$ potential with the
nearby $b^3\Pi_1$ and $B^1\Pi_1$ manifolds. Finally we report use of the $v' =
22$ line as an intermediate state for two-photon transfer of weakly bound
Feshbach molecules to the rovibrational ground state of the $X^1\Sigma^+$
manifold.
