Potential energy surface for the Li+HF→LiF+H reaction

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Abstract
The three dimensional potential energy hypersurface for Li+HF→LiF+H has been studied at the self‐consistent field (SCF) and configuration interaction (CI) levels of electronic structure theory with a medium‐sized basis set that included polarization functions. The ’’corner’’ of the reaction channel was first mapped by calculation of a lattice of points, then further calculations were carried out to characterize selected points along the minimum energy pathway more precisely. The classical reaction endothermicity was 2.9 kcal/mole, but with zero‐point corrections, the reaction was found to be exothermic by 1.7 kcal/mole. As the Li atom approaches the diatomic, it first forms a bent complex with 4.5 kcal/mole of stabilization energy before reaching the transition state. The latter, also bent with an angle of 74° was located in the exit channel and is predicted to be 10 kcal/mole above the reactants. Force constants, vibrational frequencies, and zero‐point energies of the complex and the transition state were calculated. After applying zero‐point corrections to the transition state, the threshold energy for reaction was reduced to 6.4 kcal/mole, which will probably be further reduced to ∼4 kcal by higher order correlation effects. Our results were compared with previous theoretical efforts and with qualitative theories concerned with the transition state angle and its exit bias. A qualitative discussion of the dynamics over the surface emphasizing interrelationships between the translational, vibrational energy and the LiFH angle ϑ is also presented.