Three-State Trajectory Surface Hopping Studies of the Photodissociation Dynamics of Formaldehyde on ab Initio Potential Energy Surfaces

Full-dimensional, three-state, surface hopping calculations of the photodissociation dynamics of formaldehyde are reported on ab initio potential energy surfaces (PESs) for electronic states S-1, T-1, and S-0. This is the first such study initiated on S-1 with ab initio-calculated spin orbit couplings among the three states. We employ previous PESs for S-0 and T-1, and a new PES for S-1, which we describe here, as well as new spin-orbit couplings. The time-dependent electronic state populations and the branching ratio of radical products produced from S-0 and T-1 states and that of total radical products and molecular products at three total energies are calculated. Details of the surface hopping dynamics are described, and a novel pathway for isomerization on T-1 via S-0 is reported. Final translational energy distributions of H + HCO products from S-0 and T-1 are also reported as well as the translational energy distribution and final rovibrational distributions of H-2 products from the molecular channel. The present results are compared to previous trajectory calculations initiated from the global minimum of S-0. The roaming pathway leading to low rotational distribution of CO and high vibrational population of H-2 is observed in the present calculations.