Predissociation in the B ¹Π_u state of ⁶Li⁷Li: Accidental perturbations beyond the ungerade-gerade symmetry breaking

Recently, an unusual predissociation was observed for some vibrational levels of the B ¹Π_u molecular state of ⁶Li⁷Li [Bouloufa et al., Phys. Rev. A 63, 042507 (2001)]. It was interpreted as due to the ungerade-gerade symmetry breaking that couples the B ¹Π_u quasibound levels to the 1 ¹Π_g continuum. However, the agreement between theory and experiment was not perfect for predissociation rates of three rovibrational levels, occurring for isolated quantum numbers. Here, we identify these additional perturbations as due to the rotational coupling of the 1 ¹Π_g continuum with quasibound levels of the 2 ¹Σ_g⁺ state. In addition, our method allows a calculation of the Λ-doubling in the 1 ¹Π_g state and dissociation rates of quasibound 2 ¹Σ_g⁺ levels for three isotopomers of Li₂. Comparison with experimental data is discussed.