Atmospheric Chemistry of Enols: Vinyl Alcohol + OH + O 2 Reaction Revisited.

The OH-initiated oxidation of vinyl alcohol (VA) produced by phototautomerization of acetaldehyde is thought to be a source of formic acid (FA) in the atmosphere. A recent theoretical study predicted that the VA + OH + O-2 reaction 1 proceeds by OH addition at alpha-C (66%) and beta-C (33%) of VA and that FA is a main product of reaction 1. However, the metastable reactant (anti-VA, similar to 18% at 298 K, 1.42 kcal mol(-1) higher than syn in energy) used in that study inspired us to reinvestigate reaction 1. Using the state-of-the-art quantum-chemical and kinetic calculations, we first found that a conformer of VA has a significant influence on the rate coefficient and branching ratio of reaction 1. Upon derivation, it is found that similar to 84% of reaction 1 takes place through the beta-C-addition channel and similar to 16% of reaction 1 happens by the alpha-C-addition channel. The calculated total initial rate coefficient at 298 K is 1.48 X 10(-11 )cm(3) molecule(-1) s(-1), which is in reasonable agreement with the experimental values of similar systems (vinyl ethers + OH reactions). The predicted main products of reaction 1 are glycolaldehyde and the HO2 radical, whereas FA is just a byproduct.