Stereodynamical Origin of Anti-Arrhenius Kinetics: Negative Activation Energy and Roaming for a Four-Atom Reaction.

摘要: The OH + HBr → H2O Br reaction, prototypical of halogen-atom liberating processes relevant to mechanisms for atmospheric ozone destruction, attracted frequent attention experimental chemical kinetics: the nature unusual reactivity drop from low high temperatures eluded a variety theoretical efforts, ranking this one among most studied four-atom reactions. Here, inspired by oriented molecular-beams experiments, we develop first-principles stereodynamical approach. Thermalized sets trajectories, evolving on multidimensional potential energy surface quantum mechanically generated on-the-fly, provide map visited regions at each temperature. Visualizations rearrangements bonds along trajectories and role specific angles reactants’ mutual approach elucidate mechanistic change kinetic regime (where incident reactants reorient find propitious alignment leading reaction) temperature speed hinders adjustment o...