Semiclassical dynamics on multiple electronic surfaces: Three-dimensional treatment of reactive F+H2

The role of electronic transitions in collisions is investigated for the reaction of F+H2 by combining quasiclassical Monte Carlo trajectories with a semiclassical decoupling approximation for the electronic transitions. The interaction potential is represented by three interacting potential energy surfaces constructed from one LEPS and two valence-bond type surfaces. Specific attention is focused on the reaction of excited state flourine atoms reacting to form ground state products. The reactants are initiated in either of the two spin–orbit states of the atom with the diatom in the ground vibrational state and the lowest four rotational states, at relative translational energies of 0.1, 0.2, and 0.3 eV. Cross sections are presented for each of these processes and compared to those from previous single surface calculations and experiment. Even if the reactants are initiated on the excited state surface, the reactive cross sections (which are classically forbidden) are significant. The major dynamical effects of the excited state reaction are the flow of reactant electronic energy into product internal energy. The effects of changing reactant rotational states on the product vibrational distribution was also investigated. By comparing cross sections into specific product vibrational states (v′) we find that there is a decrease in the ratio σ (v′=3)/σ (v′=2) as the rotational quantum number is increased form 0 to 3. This same trend is observed for reactions from both the ground and excited states. The ratio σ (v′=1)/σ (v′=2), however, is seen to increase as the rotational energy is increased.