First experimental observation of the doubly-excited 2/sup 1//spl Delta//sub g/ state of Na/sub 2/

We first experimentally observed the doubly-excited electronic state 2/sup 1//spl Delta//sub g/ of Na/sub 2/ dissociating into Na (3p) + Na (3p) limit. This state has the deepest interaction potential well among the 12 electronic states formed from this first doubly-excited limit. A single line Ar/sup +/ laser (total of 4 lines) was used to excite the Na/sub 2/ molecules from ground state X/sup 1//spl Sigma//sub g//sup +/ to the intermediate B/sup 1//spl Pi//sub u/ state. A solid-state pumped single mode Ti:sapphire laser was scanning from 12100 to 14300 cm/sup -1/ to search oh the optical-optical double resonance (OODR) signals. Using a combination of filters and photomultiplier tube to detect the total fluorescence from the OODR, more than 150 ro-vibrational levels from the 2/sup 1//spl Delta//sub g/ state were observed. Comparing the detected excitation intensity with the Franck-Condon factors and the observed vibrational separations with theoretical calculations, the lowest observed vibrational quantum number were assigned to /spl nu/ = 3. The T/sub e/, /spl omega//sub e/, and B/sub e/ from Dunham expansion fitting are 32540.669 cm/sup -1/, 124.039 cm/sup -1/ and 0.1186 cm-1, respectively.