Influence of water on the CH₃O˙ + O₂ → CH₂O + HO₂˙ reaction

Electronic structure calculations employing density functional theory have been used to study the effect of a single water molecule on the CH3O˙ + O2 → CH2O + HO2˙ reaction. The investigation suggests that in the presence of water the reaction barrier reduces from 3.01 kcal mol-1 to -1.86 kcal mol-1. Consequently, when we consider the bimolecular rate constants for the water catalyzed channel, they were found to be 104 to 105 times higher than that of the uncatalyzed reaction. Interestingly, the Arrhenius plot indicates a negative temperature dependency of the catalyzed channel (anti-Arrhenius behavior); as a result of this the domination of the catalyzed channel over the bare reaction increases with the lowering of the temperature. But the effective bimolecular rate constant values for the catalyzed channel were found to be approximately four orders of magnitude lower than that of the uncatalyzed one, which implies that the contribution of the catalyzed channels to the overall rate of the reaction is very small.