A pathway to ultracold bosonic ²³Na³⁹K ground state molecules

We spectroscopically investigate a pathway for the conversion of ²³Na³⁹K Feshbach molecules into rovibronic ground state molecules via stimulated Raman adiabatic passage. Using photoassociation spectroscopy from the diatomic scattering threshold in the a ³Σ⁺ potential, we locate the resonantly mixed electronically excited intermediate states |B¹Π, v=8⟩ and |c³Σ⁺, v=30⟩ which, due to their singlet-triplet admixture, serve as an ideal bridge between predominantly a ³Σ⁺ Feshbach molecules and pure X ¹Σ⁺ 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 ²³Na³⁹K molecule (X¹Σ⁺, v=0, N=0⟩) 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 ²³Na³⁹K ground state molecules.