Abstract
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]−.
Highlights
As a high clean fossil energy, how to convert methane (CH4 ) to high-density energy sources and high value-added chemicals has attracted interests of researchers from the fields of the energy science and coordination chemistry [1,2,3,4,5,6,7,8]
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 ]−
As a highly reactive free radical anion, atomic oxygen anion (O− at 2 P state) can effectively activate the C-H bond, which is involved in the ion–molecule reaction
Summary
As a high clean fossil energy, how to convert methane (CH4 ) to high-density energy sources and high value-added chemicals has attracted interests of researchers from the fields of the energy science and coordination chemistry [1,2,3,4,5,6,7,8]. As a highly reactive free radical anion, atomic oxygen anion (O− at 2 P state) can effectively activate the C-H bond, which is involved in the ion–molecule reaction. Ion–molecule reaction between O− and molecules has a profound significance in aspects of atmospheric chemistry, combustion, and environmental pollution control [9,10,11,12,13,14,15,16,17]. As a prototype reaction for ion–molecule reaction in hydrocarbon flames, the reaction between O− and methane (CH4 ) is an important example. For this reaction mechanism, Comer and Schulz reported an associative-detachment channel [18], O− + CH4 → CH3 OH + e−
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