Double many-body expansion of the two lowest potential-energy surfaces for Li3 and dynamics of the Li + Li2(v) reaction. Initial orientation and vibrational excitation effects

Abstract

The semiempirical double many-body expansion method has been used to obtain consistent analytic representations of the two lowest doublet potential-energy surfaces for Li₃. A recently reported semiempirical formulation of the three-body dynamical correlation energy has been used, which accounts for the proper dependence on the diatomic intramolecular coordinate of the Li–Li₂ long-range dispersion energy. Besides providing an accurate description of the most recent, and reliable, ab initio energies for both sheets of the potential-energy surface of the title system at the strong interaction regions, the lowest sheet of the Li₃ doublet potential-energy surface shows the correct long-range behaviour for the isotropic and leading anisotropic terms in the Legendre analysis of the Li–Li₂ interaction as a function of the Li₂ stretching coordinate. Based on the premise that only this lowest sheet is necessary, quasiclassical trajectories have been run to explore the effect of vibrational bond stretching in the Li + Li₂(v) exchange reaction. The effect of the reagent initial orientation and rotational excitation as a function of the collision energy on the lithium atom exchange dynamics has also been investigated.