RAY-YUAN CHANG, Department of Physics, National Cheng-Kung University, Tainan 70101,Taiwan(R.O.C.); THOU-JEN WHANG, CHUEN-PING CHENG, Department of Chemistry, National Cheng-Kung University, Tainan 70101, Taiwan(R.O.C.); CHIN-CHUN TSAI, Department of Physics, National Cheng-Kung University, Tainan 70101, Taiwan(R.O.C.).

The phenomenon of electronic orbital angular momentum L uncoupled from its internuclear axis has been observed in the sodium dimer using high resolution cw optical-optical double resonance spectroscopy. When L-uncoupling occurs, the degeneracy of Lambda-doubling is removed. In our experiment, the intermediate B 1 Piu state of Na2 is excited from the thermally populated ground X 1 Sigma+g state by a single line Ar+ laser. Then, a single-mode dye laser is used to probe the Rydberg states from the intermediate state. The signals are detected by monitoring the UV fluorescence from the triplet gerade states back to the a 3 Sigma+u state via collision energy transfer. Under our experimental resolution, the splitting of L-uncoupling and Lambda-doubling in both the 5 1 Deltag, 5 1 Pig states of Na2 can be measured.Total of 136 rovibronic levels with e/f parities have been assigned to the 5 1 Deltag state. The Lambda-splitting constants deduced from these data are : q0= 0.376(90)×10-4 cm-1 , qv= 0.114(6)×10-4 cm-1 , µ= 0.76(33)×10-8 cm-1. In general, the Lambda-splitting of the Delta states is considerably smaller than that of the Pi states. However, the first order splitting constants q0 and qv reported here are larger than those in the B 1 Piu state. This is due to the L-uncoupling of the Rydberg states. Total of 230 rovibrational levels are assigned to the Na2 5 1 Pig state, and the following are its correspondent Lambda-splitting constants : q0= 0.1758320898(0.017)×10-3 cm-1 , qv= -0.7124318162(0.071)×10-5 cm-1 , µ= -0.9608208561(0.8)×10-8 cm-1. The splitting of Lambda-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 1 Piu state. This indicates that the splitting of Lambda-doubling in the 5 1 Pig state is affected by both the perturbations by adjacent Sigma states and the L-uncoupling.

(grand no. NSC-95-2112-M-012-MY3).