H-abstraction mechanisms in oxidation reaction of methane and hydrogen: A CASPT2 study

• The H-abstraction mechanisms of methane and hydrogen with oxygen were investigated systematically using CASPT2 approach.
• The analysis of potential energy curve, geometric structure and electronic configuration.
• An accurate multireference method in hydrogen free-radical transfer reaction.

The oxidation of methane and hydrogen are fundamental for the understanding of the combustion or gas explosion. In this work, the H-abstraction mechanisms of two reactions: CH4 + O2 and H2 + O2 were investigated systematically using a multireference method, CASPT2. By the analysis of potential energy curve, geometric structure and electronic configuration, the H-abstraction mechanisms of the two reactions are clarified. Three H-abstraction reaction pathways occur from the triplet oxygen (3A″) and the two forms of the first electronic excited singlet oxygen (1A′ and 1A″). The pathways 1A″ and 3A″ are similar in proceeding a transition state and a van der Waals complex, respectively. The pathway 1A″ is superior in the H-abstraction reactions of the singlet oxygen-enrichment for its lower activation barrier than 3A″. The pathway 1A′ is distinct from 1A″ in dissociation to radicals directly, though their reactant energies are degenerate. A new insight is provided for the important systems like low carbon alkane oxidation.

Figure optionsDownload as PowerPoint slide