Multiscale Modeling of Interfacial Oxidation Mechanism at Air/Organic Interface: Reactions of CH2═CH-Terminated Self-Assembled Monolayer with OH•, O3, and HO2•

The first few elementary steps of the reactions of a structurally characterized CH2═CH-terminated self-assembled monolayer (SAM) with reactive oxygen species, such as OH•, HO2•, and O3 were investigated using the multilayer first principle technique (ONIOM[QCISD(T)/cc-pVTZ:MP2/6-311G(d,p):BHandHLYP/6-31G(d)]//ONIOM[BHandHLYP/6-311G(d,p):BHandHLYP/6-31G(d)]) as a proxy for the interfacial oxidation mechanism on organic aerosol surfaces. The energetics of the reactions is compared with the analogous QCISD(T)/cc-pVTZ//BHandHLYP/6-311G(d,p) gas-phase results, to measure the energetic consequences of the presence of the surrounding alkene chains. All of the reactions studied are affected in such a way that the relative energies of the interfacial reactions became lower by the average value of 11.5 ± 6.1 kJ/mol than the corresponding gas-phase values. Because of this effect, interfacial H-abstractions by OH• on both allylic and vinylic positions have submerged barriers (ΔE0‡ = −5.4 kJ/mol and ΔE0‡ = −5.8 kJ/mol...