Effect of Reagent Vibrational Excitation on the Dynamics of F + H2(v = 1, j = 0) → HF(v', j') + H Reaction.

The reaction of fluorine atom with vibrationally excited H2 at v = 1 has been studied using a high resolution crossed molecular beam apparatus at collision energies of 0.52 and 0.90 kcal/mol. Product HF rotational state-resolved differential cross sections (DCSs) were measured at v' = 2, 3, 4 levels. The product angular distributions are predominantly backward scattered except for a small forward signal of HF(v' = 4) at 0.90 kcal/mol. At the collision energy of 0.52 kcal/mol, the forward scattering peak of the HF(v' = 2) product, which arises in F + H2(v = 0) reaction from the Feshbach resonances, disappears in F + H2(v = 1) reaction. Oscillatory structures do not appear in the backward direction of the scattering as the collision energy increases from 0.4 to 2.0 kcal/mol, indicating there are no explicit reaction resonances in the F + H2(v = 1, j = 0) → HF + H reaction in the studied energy range. Quantum dynamics calculations on a highly accurate potential energy surface are in good agreement with the experimental results and reveal that the reaction occurs via likely a direct abstraction mechanism, not via long-lived reactive resonances.