Experimental study of the Na2 31Î g state

The 31Πg state of Na2 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 X1Σg+ to the intermediate B1Πu state. Then a single mode Ti:sapphire laser is used to probe the 31Πg state. Violet fluorescence from highly Rydberg excited states (mainly 23Πg or 33Πg states which are transferred from 31Πg state via collisions) to the a3Σu+ 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 31Πg state are deduced from all the observed rovibrational levels.