Photodissociation dynamics of formaldehyde initiated at the T1/S0 minimum energy crossing configurations.

The photodissociation dynamics of H(2)CO is known to involve electronic states S(1), T(1) and S(0). Recent quasiclassical trajectory (QCT) calculations, in conjunction with experiment, have identified a "roaming" H-atom pathway to the molecular products, H(2)+CO [Townsend; et al. Science 2004, 306, 1158.]. These calculations were initiated at the global minimum (GM) of S(0), which is where the initial wave function is located. The "roaming" mechanism is not seen if trajectories are initiated from the molecular transition state saddle point (SP). In this Letter we identify the minimum energy-crossing configurations and energy of the T(1)/S(0) potentials as a step toward studying the multisurface nature of the photodissociation. QCT calculations are initiated at these configurations on a revised potential energy surface and the results are compared to those initiated, as previously, from the S(0) GM as well as the S(0) SP. The product state distributions of H(2) + CO from trajectories initiated at the T(1)/S(0) crossing are in excellent agreement with those initiated at the S(0) GM.