Experimental study of the NaK 3Π3 double minimum state

We have used the Doppler-free, perturbation-facilitated optical-optical double-resonance technique to investigate the vibrational, rotational, and hyperfine structure of the 3Π3 double minimum state of NaK. Since this electronic state arises from an avoided crossing with the nearby 4Π3 state, we observe striking patterns in the data that provide a sensitive probe of the electronic wave function in the various regions of the double well potential. A single-mode cw dye laser excites 2(A)Σ+1(vA,J)∼1(b)ΠΩ=03(vb,J) mixed singlet-triplet “window” levels from thermally populated rovibrational ground state levels, 1(X)Σ+1(vX,J±1). Further excitation by a single-mode cw Ti:sapphire laser selects various 3Π03(vΠ,JΠ) rovibrational levels, which are detected by observing direct 3Π03→1(a)Σ+3 fluorescence in the green spectral region. Using the inverse perturbation approximation method, we have determined a 3Π03 potential curve that reproduces the measured energies to ∼0.24cm−1. In addition, the hyperfine and spin–orbit constants, bF and Av, have been determined for each region of the potential curve.