Λ-Doubling investigation of the 5¹Π_g Rydberg state of Na₂ using optical-optical double resonance spectroscopy

The splitting of Λ-doubling in the 5¹Π_g Rydberg state of Na₂, which dissociates to Na(3s) + Na(4d), has been measured using the high-resolution cw optical-optical double resonance technique. The observed data are in the range of 0 ≤ v ≤ 22 and 11 ≤ J ≤ 83 with Λ-doubling revealed. A set of Dunham coefficients with Λ-doubling constants has been obtained from the experimental results. The splitting of Λ-doubling increases quadratically with the rotational quantum number J and weakly depends on the vibrational quantum number v. These splitting constants are much larger than those in the Na₂ B ¹Π_u state, which dissociates to Na(3s) + Na(3p). This indicates that the splitting of Λ-doubling in the 5¹Π _g state is affected by both the perturbations by adjacent Σ states and the L-uncoupling.