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

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+O-2 and H-2+O-2 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 ((3)A '') and the two forms of the first electronic excited singlet oxygen ((1)A' and (1)A ''). The pathways (1)A '' and (3)A '' are similar in proceeding a transition state and a van der Waals complex, respectively. The pathway (1)A '' is superior in the H-abstraction reactions of the singlet oxygen-enrichment for its lower activation barrier than (3)A ''. The pathway (1)A' is distinct from (1)A '' 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. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.