Empirical Evaluation of the London Potential Energy Surface for the H + H2 Reaction

Abstract

An empirical potential surface for the hydrogen exchange reaction is derived from the simplest form of the London approximation (neglecting overlap), by evaluating the Coulomb and exchange integrals from the potential curves for the ¹Σ_g⁺ and ³Σ_u⁺ states of H₂. This procedure gives an activation energy of 8.9±1.2 kcal/mole, in good agreement with the experimental value of 8.0±0.5 kcal/mole. The potential surface has a single saddle point, and the H: complex is linear and symmetrical, with a bond length of 0.96 Å. Simple, explicit formulas for the activation energy and the vibrational force constants are also obtained. The results emphasize the important contribution from the triplet repulsion between the end atoms with parallel spins in the complex.