Tuesday, 8 January 2013
Carbonyl oxides (Criegee intermediates or CIs) are produced in the process of olefins ozonolysis and can decompose to form OH or engage in bimolecular reactions with SO2, H2O, CO2, aldehydes, etc. In particular, the reaction of carbonyl oxides with SO2 can contribute to conversion of SO2 to H2SO4, a crucial step in the formation of sulfate aerosols and represents. Since isoprene is one of the most abundant hydrocarbons naturally emitted by the terrestrial biosphere and ozonolysis of isoprene provides an important source of nighttime OH radicals on the regional scale. In this study, the potential enery surface (PES) and mechanism of the reaction between the stabilized syn carbonyl oxide arising from isoprene ozonolysis and SO2 are investigated by using density functional theory (DFT) and ab initio (MP2 and CCSD(T)) methods. The mechanism involving the formation of a preactivation complex and an adduct, followed by two decomposition pathways leading to methyl vinyl ketone (MVK) + SO3 and an ester + SO2 is described. The results reveal a profound impact of the title reaction on SO2 oxidation and OH formation yield from isoprene ozonolysis under atmospheric conditions.
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