  We spectroscopically investigate a pathway for the conversion of
$^{23}\textrm{Na}^{39}\textrm{K}$ Feshbach molecules into rovibronic ground
state molecules via STImulated Raman Adiabatic Passage (STIRAP). Using
photoassociation spectroscopy from the diatomic scattering threshold in the
$a^3\Sigma^+$ potential, we locate the resonantly mixed electronically excited
intermediate states $|B^1\Pi, v=8\rangle$ and $|c^3\Sigma^+, v=30\rangle$
which, due to their singlet-triplet admixture, serve as an ideal bridge between
predominantly $a^3\Sigma^+$ Feshbach molecules and pure $X^1\Sigma^+$ ground
state molecules. We investigate their hyperfine structure and present a simple
model to determine the singlet-triplet coupling of these states. Using
Autler-Townes spectroscopy, we locate the rovibronic ground state of the
$^{23}\textrm{Na}^{39}\textrm{K}$ molecule ($|X^1\Sigma^+, v=0, N=0\rangle$)
and the second rotationally excited state $N=2$ to unambiguously identify the
ground state. We also extract the effective transition dipole moment from the
excited to the ground state. Our investigations result in a fully characterized
scheme for the creation of ultracold bosonic $^{23}\textrm{Na}^{39}\textrm{K}$
ground state molecules.
