Classical trajectory studies of alkali atom-alkali dimer exchange reactions : Na+Li₂ and Li+Na₂

Abstract

The endoergic and exoergic alkali atom-alkali dimer exchange reactions, Na+Li₂→NaLi+Li and Li+Na₂→LiNa+Na, have been studied using classical trajectory methods on LEPS surfaces exhibiting shallow potential wells at small internuclear separations. For both systems the total reaction cross section, collision lifetime, differential reaction cross section and product energy disposal were calculated for a range of initial collisional energies. Comparison with the results from statistical theories for the energy disposal and angular scattering show good agreement at the lower collisional energies. At these energies the reactions are found to proceed via the formation of a long-lived complex which is non-rigid and non-linear; as the energy is increased the reaction dynamics become direct. For the exoergic reaction about 60–70 per cent of the total available energy goes into internal motion of the product molecule; for the endoergic system, the fraction is 50–60 per cent. The effect of vibrational excitation of the reactant molecules was also investigated and it was found that for the endoergic system the total reaction cross section was increased by up to a factor of six when the reactant alkali dimer was vibrationally excited. The calculated reaction cross sections and energy disposal for the exoergic reaction Li+Na₂ are similar to the results from molecular beam studies on some alkali atom-alkali dimer exchange reactions.