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Full Dimension Potential Energy Surface and Low Temperature Dynamics of the H2CO + OH —> HCO + H2O reaction

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Authors : A. Zanchet, P. Del-Mazo, A. Aguado, O. Roncero, E. Jiménez, A. Canosa, M. Agúndez, and J. Cernicharo
Abstract : A new method is proposed to analytically represent the potential energy surface of reactions involving polyatomic molecules capable of accurately describing long-range interactions and saddle points, needed to describe low-temperature collisions. It is based on two terms, a reactive force field term and a manybody term. The reactive force field term accurately describes the fragments, long-range interactions among them and the saddle points for reactions. The many-body term increases the desired accuracy everywhere else. This method has been applied to the OH + H2CO - H2O + HCO reaction, giving a barrier of 27.4 meV. The simulated classical rate constants with this potential are in good agreement with recent experimental results [Ocaña et al., Astrophys. J., 2017, submitted], showing an important increase at temperatures below 100 K. The reaction mechanism is analyzed in detail here, and explains the observed behavior at low energy by the formation of long-lived collision complexes, with roaming trajectories, with a capture observed for very long impact parameters, 4100 a.u., determined by the long-range dipole–dipole interaction.
Journal : Phys. Chem. Chem. Phys 20[8], 5415-5426 (2018)