Quasiclassical trajectory study of the reaction O(3P)+H₂→ OH+H. the effects of the location of the potential energy barrier, vibrational excitation and isotopic substitution on the dynamics

Three dimensional quasiclassical trajectory calculations were carried out for the nearly thermoneutral reaction of oxygen atoms O(³P) with hydrogen molecules (H₂,D₂, and HD). Three LEPS potential energy surfaces, all having the same barrier height but with slightly different locations, were used for the calculations. Calculations for various initial vibrational states of H₂ were performed for reaction temperatures of 300, 500, and 900 K. For the reactions O+D₂ and O+HD calculations were carried out for the ground vibrational state for 500 and 900 K. The trajectory calculations showed that the rate constants are very sensitive to the position of the potential energy barrier. They increase or decrease considerably when the barrier is shifted slightly in the direction of the exit valley or entry valley, respectively. The rate of the reaction O+H ₂(v)→OH+H was found to be enhanced significantly with vibrational excitation of the H₂. At 300 K the rate constant for v=1 was found to be larger than for v=0 by three to four orders of magnitude, depending on the potential energy surface used. The vibrational energy of the reactants E_v was found to be converted very efficiently into vibrational energy of the products E′_v. The results of the present trajectory calculations are compared with earlier results for another nearly thermoneutral reaction Cl+H₂→HCl+H and with experimental results for the rate constants and kinetic isotope effects.