Trajectory surface hopping study of the C+CH reaction

The influence of electronically nonadiabatic transitions in the C(P-3(g)) + CH(X (2)Pi) --> C-2(X (1)Sigma(g)(+), a (3)Pi(u)) + H(S-2(g)) reaction is investigated by using Tully's fewest-switches version of the trajectory surface hopping method. A diabatic model of the first two (2)A' potential energy surfaces coupled by a conical intersection is used. The diatomic CH has the internal state (nu = 0, j = 0) and batches of 20 000 trajectories are computed for four collision energies, E = 0.1, 0.3, 0.5 and 0.7 eV. We find that the reaction dynamics does not exhibit a statistical character, despite the existence of deep wells along the reaction path. Only the distribution of scattering angle shows a good agreement between trajectories and phase space theory results. A strong excess of vibrational energy is disposed on both electronic products C-2(X (1)Sigma(+) g) and C-2(a (3)Pi(u)), correlated with a lack of recoil energy. With all trajectories starting on a single potential surface, we obtain an electronic branching ratio X : a close to 2 : 3, only slightly dependent on the collision energy.