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 (CH(4)) 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 OCH(3)(−) and H is also observed in this study. Three typical O(−) attack modes with reference to the pyramid structure of CH(4) 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 CH(4), the major pathway to produce OH(−) and CH(3) is preferred by the direct H-abstraction and the minor pathway to produce H and OCH(3)(−) is the roaming reaction via the transient negative ion [HO-CH(3)](−).