Experimental study of the Na2 31Πg state

The 3 1 Π g state of Na 2 is experimentally investigated by using high resolution cw optical–optical double resonance spectroscopy. A single line Ar + laser (total of 9 lines) is used to pump the sodium dimers from thermally populated ground state X 1 Σ g + to the intermediate B 1 Π u state. Then a single mode Ti:sapphire laser is used to probe the 3 1 Π g state. Violet fluorescence from highly Rydberg excited states (mainly 2 3 Π g or 3 3 Π g states which are transferred from 3 1 Π g state via collisions) to the a 3 Σ u + state is monitored by a filtered photomultiplier tube and a lock-in amplifier. Compared with previous studies [C.C. Tsai, J.T. Bahns, W.C. Stwalley, J. Chem. Phys. 99 (1993) 7417], a wider range of rotational quantum numbers of data field are observed. A set of Dunham coefficients and the Rydberg–Klein–Rees potential energy curve of the 3 1 Π g state are deduced from all the observed rovibrational levels.