Observation of the 4 ³Σ_g⁺, 3 ³Π_g, 2 ³Δ_g, and b ³Π_u states of ³⁹K₂ by perturbation facilitated optical-optical double resonance spectroscopy

The 4 ³Σ_g⁺, 3 ³Π _g, and 2 ³Δ_g states of K₂ have been studied by perturbation facilitated optical-optical double resonance spectroscopy for the first time. Molecular constants of those states are derived and compared with theoretical calculations. Varying the trial vibrational quantum numbers of these upper states, absolute vibrational quantum number assignments are obtained by comparison between the observed resolved fluorescence intensities and the calculated Franck-Condon factors. The Rydberg-Klein-Rees potential curves are constructed and compared with theoretical calculations. Finally, the observation of the lowest "dark" vibrational levels of the b ³Π_u state by resolved fluorescence from the 2 ³Δ_g state confirmed the absolute vibrational numbering of this state and allowed refinement of the b ³Π_u molecular constants.