Semiempirical pseudopotential surfaces for chemical reactions: The (AB)+X-dialkali halide systems

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Abstract
A generalization of the Roach-Child semiempirical pseudopotential calculation for K + NaCl to several analogous dialkali halide systems has been used to elucidate the chemical interactions governing the reaction dynamics. The Li + LiF ground-state potential surface, which exhibits a ∼ 20 kcal/mole basin for isosceles Li2F, is qualitatively similar to one obtained in a recent configurational interaction calculation. It is shown that regions of the Na2Cl ground-state surface corresponding to Na2 + interacting with Cl- can be described in terms of an ion-pair Rittner potential model similar to that employed for the alkali halides. Chemical trends in the triangular complex well depths satisfactorily account for the experimentally observed transition between the collision complex mechanism (Rb + KCl) and the osculating complex model (Li + KBr) for the alkali-alkali halide exchange reactions at thermal energies. For collinear configurations with the alkalis on opposite ends, avoided intersections between the lowest two potential surfaces are characterized in terms of diabatic surfaces computed from truncated basis sets. Crossings of these surfaces account for the vibrational-electronic energy transfer between alkali atoms and vibrationally excited alkali halides. The ionic X - + A 2 + potential surfaces are used to predict the product electronic excitation and partitioning of exoergicity in reactions of halogen atoms with alkali dimer molecules.