Theoretical studies of the O₂ + methane, ethane and propane reactions

The reactions of ground state molecular oxygen with short chain alkanes were studied using electronic structure calculations and molecular dynamics simulations. The energy profiles of the O₂ + RH → HO₂ + R (H abstraction) and O₂ + RH → RO₂ + H (H elimination) reactions (R=CH₃, C₂H₅, C₃H₇) were characterized using ab initio and density functional theory methods. Both reactions were strongly endothermic, and whereas H abstraction did not show any barrier other than the reaction energy, the lowest energy H elimination saddle point was reminiscent of that of an SN2 reaction. Direct dynamics calculations were carried out using the classical trajectory method in conjunction with a high-quality semiempirical Hamiltonian. Excitation functions, products energy, and angular distributions revealed the importance and dynamics characteristics of the different reaction channels as well as the microscopic mechanisms of reaction. This is an abstract of a paper presented at the 228th ACS National Meeting (Philadelphia, PA, 8/22-26/2004).