The vinyl hydroperoxide (VHP) formed in alkene ozonolysis is the most important non-photochemical source of hydroxyl radical (OH) in the atmosphere. Recent experimental and computational studies suggest that, in spite of a low barrier to peroxy bond homolysis, the chemically activated VHP may not be a stoichiometric source of OH under atmospheric conditions. We have performed CBS-QB3 and equation-of-motion spin-flip coupled-cluster (EOM-SF-CC) electronic structure calculations to quantify both dissociation and rearrangement pathways for the VHPs derived from acetaldehyde oxide and methyl vinyl carbonyl oxide, two of the most common Criegee intermediates formed in gas-phase ozonolysis. We find that EOM-SF-CC calculations that include all single and double excitations and a perturbative estimate of the effect of triple excitations (CCSD(dT)) predict energetics for peroxy bond homolysis that agree to within 1 kcal/mol of the predictions of far more demanding multi-reference CISD+Q calculations. This suggests that EOM-SF-CCSD(dT) theory provides a convenient and accurate way to treat diradical species commonly formed in atmospheric reactions.  We also provide computational evidence that rearrangements of the VHP to alcohols can partially account for less-than-expected OH yields from alkene ozonolysis.

Quantum chemical modeling of atmospheric free radical production from vinyl hydroperoxides

248th National Meeting (2014)

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