Predissociation Induced by Ungerade-Gerade Symmetry Breaking in ⁶Li⁷Li Molecule

In the recent sub-Doppler experiment on the B¹Π_u state of the Li₂ molecule by Bouloufa et al. [J. Chem. Phys. 111, 1926 (1999)], where the dissociation of vibrational levels due to the tunneling through the potential barrier was investigated, several vibrational levels with abnormally large dissociated rates were observed in the case of the ⁶Li⁷Li isotopomer. This dynamical effect cannot be explained by tunneling as in the case of ⁶Li₂ or ⁷Li₂. A simple model of coupling between B¹Π_u and 1¹Π_g states involving the u-g symmetry breaking for ⁶Li⁷Li is proposed. Rates of the B¹Π_u predissociated levels due to this coupling are calculated. A good agreement with the experiment is found.