Observation of the 7Π_g State of Na₂ by Optical−Optical Double Resonance Spectroscopy

The 7¹Π_g Rydberg state of Na₂ correlating with the separated atom limit Na(3s) + Na(5p) has been observed using high-resolution cw optical−optical double resonance spectroscopy. A total of 104 identified rovibrational levels in the range v = 0−12 and 11 ≤ J ≤ 44 have been assigned to the 7¹Π_g state. Dunham coefficients were determined, and the Rydberg−Klein−Rees potential curve in the range of R = 2.99−4.66 Å was derived for the 7¹Π_g state using the observed quantum levels. The important molecular properties are the potential minimum T_e = 36 633.00(23) cm^-1 at R_e = 3.6313(29) Å, ω_e = 115.75(13) cm^-1, and B_e = 0.111 22(17) cm^-1. A detailed discussion of this investigation of the 7¹Π_g state is provided.