Near-infrared bound-free emission from the NaK molecule

We report the observation of bound–free emission corresponding to the lowest triplet transition 1 3Π→1 3Σ+ of the NaK molecule. In the experiment, specific levels of the upper triplet state were populated directly from the ground state by virtue of spin–orbit induced perturbations between the 1 3Π0 and 2 1Σ+ states. Oscillations in the fluorescence spectra between 1.1 and 1.6 μm reflect the probability distribution (wave function squared) in the bound upper state. We have also carried out quantum mechanical simulations of the fluorescence spectra, based on recent ab initio calculations of the relevant potential curves. These simulations verify the identification of this near-infrared emission and provide a critical test for the calculated potentials.