Ab Initio Molecular Dynamics Simulation Study on the Stereo Reactions between Atomic Oxygen Anion and Methane.

Ion⁻molecule reaction between atomic oxygen anion (O) and methane (CH₄) has been systematically investigated employing the on-the-fly ab initio molecular dynamics simulations. Besides the major H-abstraction process as the exothermic reaction studied widely, an endothermic pathway to produce OCH₃ and H is also observed in this study. Three typical O attack modes with reference to the pyramid structure of CH₄ fixed in space have been considered. It was found that the internal motions of the radical products are significantly dependent on the O attack modes. As for the reaction between O and the thermally vibrating CH₄, the major pathway to produce OH and CH₃ is preferred by the direct H-abstraction and the minor pathway to produce H and OCH₃ is the roaming reaction via the transient negative ion [HO-CH₃].