DISSOCIATION ENERGY OF LI2 FROM LASER-EXCITED FLUORESCENCE

The fluorescence spectra B 1∏u-X 1∑g+ of the molecular species 6Li2, 6Li7Li, and 7Li2, excited by the cw lines of the argon ion laser, have been observed and analyzed. Based on a short Birge-Sponer extrapolation of the vibrational levels of the ground state, the dissociation energy for the Li 2 molecule has been determined to be D0 0=1.026±0.006 eV. This value, combined with the dissociation limit of the upper state determined by Loomis and Nusbaum, proves that there is a hump of about 0.12±0.04 eV above the asymptote of the potential curve of the Li2 B 1∏u state. Improved rotational and vibrational constants of the ground state of Li2 have also been obtained. A new technique is described which utilizes collision-induced rotational transfer to facilitate the v′, J′ assignment of the excited levels.