Classical Trajectory Analysis of the Reaction F+H2→HF+H

Abstract

A classical trajectory analysis has been made for the reaction F+H2→HF+H using a semiempirical potential energy surface. The reaction cross sections, energy distributions among reaction products, and angular distributions of products were determined as functions of initial relative velocity for low-lying rotation–vibration states of H2 from Monte Carlo averages over a large number of trajectories. The modified London–Eyring–Polanyi–Sato surface used is characterized by a 1.68 kcal barrier in the entry valley with a net drop of 31.3 kcal to the exit valley occurring with F approaching H2. The reaction cross sections for H2 with υ = 0, J = 1 increased with relative velocity from a threshold value at a translational energy of 2.1 kcal to ∼ 6 Å2 at 14 kcal. Rotational energy had little effect on the cross sections. For υ = 1, J = 1 the translational energy threshold was slightly lower and the upper limit to cross sections was ∼ 8 Å2. The HF product was found to be strongly excited vibrationally with an average of ∼ 60% of the reaction energy released to vibrational excitation. Reaction rate constants determined by integrating the cross sections for thermal distributions of reactants were fitted to an Arrhenius rate expression k = A exp(− Ea / RT) with A = 1014.1cm3mole−1·sec−1 and Ea = 2.72 kcal. The results are in qualitative agreement with existing measurements of over-all reaction rates and with product energy distributions determined in measurements of infrared chemiluminescence. Results from a limited number of trajectories for the reaction F+D2→DF+F are also presented.