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

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 $\text{υ\hspace{0.17em}=\hspace{0.17em}0, J\hspace{0.17em}=\hspace{0.17em}1}$ increased with relative velocity from a threshold value at a translational energy of 2.1 kcal to ∼ 6 Ų at 14 kcal. Rotational energy had little effect on the cross sections. For $\text{υ\hspace{0.17em}=\hspace{0.17em}1, J\hspace{0.17em}=\hspace{0.17em}1}$ the translational energy threshold was slightly lower and the upper limit to cross sections was ∼ 8 Ų. 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 $\mathrm{k\hspace{0.17em}=\hspace{0.17em}A}\exp {\mathrm{(-\hspace{0.17em}E}}_a\mathrm{\hspace{0.17em}/\hspace{0.17em}RT)}$ with ${\text{A\hspace{0.17em}=\hspace{0.17em}10}}^{\text{14.1}}{\mathrm{cm}}^3{\mathrm{mole}}^{\text{−1}}·{\sec }^{\text{−1}}$ and $E_a\text{\hspace{0.17em}=\hspace{0.17em}2.72}\mathrm{kcal}$ . 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.