Quasiclassical trajectory investigation of the reaction O(1D)+H2

Abstract

A theoretical investigation of the energetics and dynamics of the O(1D)+H2 reaction is reported. Two different valence bond diatomics-in-molecules potential energy surfaces were used which differed only in the presence or absence of a small barrier to the C2v approach. The results of quasiclassical trajectory calculations were completely different on the two surfaces and showed that the dynamics of this exothermic reaction are sensitive to features of the surface at large internuclear distances. Reactions were found to occur by two possible mechanisms. In one mechanism, the oxygen atom abstracts a hydrogen atom from the end of the molecule in a direct reaction. Alternatively, the oxygen atom inserts into the H–H bond to form a collision complex which subsequently breaks apart. At all collision energies, the vibrational distribution of products from insertion/decomposition events is statistical while that of abstraction events is centered about v′ = 2. An inversion in the total populations of the levels v′ = 1 and v′ = 2 is observed at a collision energy of 5.0 kcal mol. Insertion/decomposition reactions lead to hot rotational distributions of products. A transition from cold rotational distributions at low collision energies to a hot distribution at the highest collision energy is observed for abstraction reactions. At low collision energy, the differential cross section for insertion/decomposition reactions indicates a collision complex is formed whose lifetime is less than the rotational period. As the collision energy increases, a transition to the formation of a long-lived complex occurs.