Abstract: | The Na2(3sσg)(4sσg) 23Σ+g state of Na2 has been observed and studied by cw perturbation-facilitated optical-optical double-resonance (PFOODR) spectroscopy for the first time. A single-mode dye laser and a Ti-sapphire laser served as the pump and the probe lasers, respectively. A total of 543 PFOODR excitation signals have been assigned to the 23Σ+g ← b3Π1u transitions. Absolute vibrational numbering was determined by counting nodes in the 23Σ+g → a3Σ+u bound-free spectra. Spectroscopic constants and the corresponding RKR potential energy curve are presented in this vsork. The values of Te, Re, and De, are found to be 25 551.237(49) cm−1, 3.53463(35) Å, and 6211.5(1) cm−1 respectively. |