Water Vapor does not Catalyze the Reaction between Methanol and OH Radicals

Recent works [Jara‐Toro et al., Angew. Chem. Int. Ed. 2017, 56, 2166 and PCCP 2018, 20, 27885] suggest that the rate coefficient of OH reactions with alcohols would increase by up to 2 times from dry to high humidity. This finding would have an impact on the budget of alcohols in the atmosphere and that it may explain differences in measured and modeled methanol concentrations. The results were based on a relative technique carried out in a small Teflon bag, which might suffer from wall reactions. We have re‐investigated this effect using a direct fluorescence probe of OH radicals, and no catalytic effect of H2O could be found. Experiments in a Teflon bag were also carried out, but we were not able to reproduce the results of Jara‐Toro et al. Further theoretical calculations show that the water‐mediated reactions have negligible rates compared to the bare reaction and that even though water molecules can lower the barriers of reactions, it cannot make up for the entropy cost.

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