Supporting data for Formation of Highly Oxidized Molecules from NO3 Radical Oxidation of Δ-3-Carene: A Computational Mechanism
Draper, Danielle et al. (2019), Supporting data for Formation of Highly Oxidized Molecules from NO3 Radical Oxidation of Δ-3-Carene: A Computational Mechanism , Dryad, Dataset, https://doi.org/10.7280/D1VT0B
NO3 radical oxidation of most monoterpenes is a significant source of secondary organic aerosol (SOA) in many regions influenced by both biogenic and anthropogenic emissions, but there are very few published mechanistic studies of NO3 chemistry beyond simple 1st generation products. Here, we present a computationally-derived mechanism detailing the unimolecular pathways available to the 2nd generation of peroxy radicals following NO3 oxidation of Δ-3-carene, defining generations based on the sequence of peroxy radicals formed rather than number of oxidant attacks. We assess five different types of unimolecular reactions, including peroxy and alkoxy radical (RO2 and RO) hydrogen shifts, RO2 and RO ring closing (e.g. endoperoxide formation), and RO decomposition. Rate constants calculated using quantum chemical methods indicate that this chemical system has significant contribution from both bimolecular and unimolecular pathways. The dominant unimolecular reactions are endoperoxide formation, RO H-shifts, and RO decomposition. However, the complexity of the overall reaction is tempered as only 1 or 2 radical propagation pathways dominate the fate of each radical intermediate. Chemical Ionization Mass Spectrometry (CIMS) measurements using the NO3- reagent ion during Δ-3-carene + NO3 chamber experiments show products consistent with each of the three types of unimolecular reactions predicted to be important from the computational mechanism. Moreover, the SIMPOL group contribution method for predicting vapor pressures suggests that a majority of the closed-shell products inferred from these unimolecular reactions are likely to have low enough vapor pressure to be able to contribute to SOA formation.
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National Science Foundation, Award: AGS-1762098
National Science Foundation, Award: AGS-1762106