DOUBLE MANY-BODY EXPANSION OF THE 2 LOWEST POTENTIAL-ENERGY SURFACES FOR LI-3 AND DYNAMICS OF THE LI-2(UPSILON) REACTION - INITIAL ORIENTATION AND VIBRATIONAL-EXCITATION EFFECTS(LI)

The semiempirical double many-body expansion method has been used to o btain consistent analytic representations of the two lowest doublet po tential-energy surfaces for Li3. A recently reported semiempirical for mulation of the three-body dynamical correlation energy has been used, which accounts for the proper dependence on the diatomic intramolecul ar coordinate of the Li-Li2 long-range dispersion energy. Besides prov iding an accurate description of the most recent, and reliable, ab ini tio energies for both sheets of the potential-energy surface of the ti tle system at the strong interaction regions, the lowest sheet of the Li3 doublet potential-energy surface shows the correct long-range beha viour 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 neces sary, quasiclassical trajectories have been run to explore the effect of vibrational bond stretching in the Li + Li2(v) exchange reaction. T he effect of the reagent initial orientation and rotational excitation as a function of the collision energy on the lithium atom exchange dy namics has also been investigated.