Optical–optical double resonance polarization spectroscopy of highly excited states of 23Na39K

The Doppler-free high resolution spectrum of the transitions to highly excited states of the 23Na39K molecule was measured by using the technique of the optical–optical double resonance polarization spectroscopy. Several highly excited states 1Σ+, 1Π, and 1Δ were found, and the molecular constants for these states were determined. The vibrational numbering of the 1Δ state (G 1Δ state) was estimated, and the potential energy curve was calculated by the Rydberg–Klein–Rees method. Many perturbed lines were observed. The indirect perturbation between 1Σ+ and 1Δ levels through the L-uncoupling interaction with a distant 1Π state was identified. The hyperfine splittings were observed in transition lines to a 3Π state, which is perturbed by a 1Σ+ state.