A roaming pathway leads to unexpected water+vinyl products in C₂H₄OH dissociation

E. Kamarchik, L. Koziol, H. Reisler, J.M. Bowman, and A.I. Krylov
J. Phys. Chem. Lett. 1, 3058 – 3065 (2010)

We report molecular dynamics simulations of the unimolecular dissociation of energetic C₂H₄OH radicals using a full-dimensional potential energy surface (PES). The PES is a permutationally invariant fit to density functional theory (DFT) and coupled-cluster with single and double excitations (CCSD) calculations. Quasiclassical trajectories are initiated on the surface using microcanonical sampling at a total energy of 85.0 kcal/mol. The trajectories reveal a previously unexplored roaming channel leading to the formation of water after an initially frustrated dissociation to hydroxyl plus ethene. The transition state (TS) corresponding to direct water production is energetically inaccessible. However, the roaming pathway finds a lower-energy path via frustrated dissociation to hydroxyl that makes water+vinyl production feasible. The trajectory calculations suggest that the roaming pathway constitutes a minor (a few percent) but robust channel of the overall C₂H₄OH dissociation. The mechanism of the roaming reaction is analyzed in terms of the geomterical proximity of the TS's leading to OH loss and internal abstraction as well as the partitioning of vibrational energy into different modes.

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