Computational study of the reactions of methane with XO radicals (X = F, Cl, or Br): Implications in combustion chemistry

Theoretical calculations were carried out on the H atom abstraction reactio n from methane by XO (X = F, Cl or Pr) radical attack. Geometry optimizatio ns and vibrational frequency calculations were performed using three method s: Moller-Plesset second-order perturbation theory (MP2), quadratic configu ration interaction in the space of single and double excitations (QCISD), a nd the "hybrid" three-parameter exchange functional with Becke's gradient c orrected exchange and Lee-Yang-Parr correlation functional (B3LYP). Single- point energy calculations were performed using several high quality basis s ets. Canonical transition-stale theory was used to predict the rate constan ts as a function of temperature (700-2500 K), and three-parameter Arrhenius expressions were obtained by fitting to the computed rate constants. The p ossible impact of the title reactions in combustion chemistry is also discu ssed.