Quasiclassical trajectory study of formaldehyde unimolecular dissociation:: H2CO→H2+CO, H+HCO -: art. no. 114313

We report quasiclassical trajectory calculations of the dynamics of the two reaction channels of formaldehyde dissociation on a global ab initio potential energy surface: the molecular channel H2CO -> H-2+CO and the radical H2CO -> H+HCO. For the molecular channel, it is confirmed that above the threshold of the radical channel a second, intramolecular hydrogen abstraction pathway is opened to produce CO with low rotation and vibrationally hot H-2. The low-j(CO) and high-nu(H2) products from the second pathway increase with the total energy. The competition between the molecular and radical pathways is also studied. It shows that the branching ratio of the molecular products decreases with increasing, energy, while the branching ratio of the radical products increases. The results agree well with very recent velocity-map imaging experiments of Suits and co-workers and solves a mystery first posed by Moore and co-workers. For the radical channel, we present the translational energy distributions and HCO rotation distributions at various energies. There is mixed agreement with the experiments of Wittig and coworkers, and this provides an indirect confirmation of their speculation that the triplet surface plays a role in the formation of the radical products. (c) 2005 American Institute of Physics.