Molecular Dynamics Study of Combustion Reactions in Supercritical Environment. Part 3: Boxed MD Study of CH₃ + HO₂ → CH₃O + OH Reaction Kinetics

The kinetics of reaction CH₃ + HO₂ → CH₃O + OH in supercritical carbon dioxide media at pressures from 0.3 to 1000 atm in the temperature range (600-1600) K was studied using boxed molecular dynamics simulations at QM/MM theory level with periodical boundary conditions. The mechanism of this process includes two consecutive steps: formation and decomposition of CH₃OOH intermediate. We calculated the activation free energies and rate constants of each step, then used Bodenstein's quasistationary concentrations approximation to estimate the rate constants of the reaction. On the basis of the temperature dependence of the rate constants, parameters in the extended Arrhenius equation were determined. We found that reaction rate of each step, as well as overall reaction, increases with increasing CO₂ pressure in the system. The most effective zone for the process is T = 1000-1200 K, and the CO₂ pressure is about 100 atm.