Direct observation of the particle-phase bicyclic products from OH-initiated oxidation of 1,3,5-trimethylbenzene under NOx-free conditions
Résumé
The OH initiated oxidation of 1,3,5-trimethylbenzene (1,3,5-TMB) under NOx-free conditions has been investigated by using a home-made vacuum ultraviolet (VUV) photoionization aerosol mass spectrometer complemented by high-level theoretical computations. The chemical composition of the nascent particles from the oxidation reaction is measured on-line and the high mass O 2-bridged bicyclic compounds in the particle phase are directly observed and determined, with the aid of the deuterated 1,3,5-TMB experiments to confirm the species' assignment. To illuminate the formation of the O 2-bridged bicyclic compounds, the potential energy surfaces of the reaction of the bicyclic peroxy radical (BPR) with the hydroperoxy radical (HO 2), and of the self-reaction of the BPR radical, have been theoretically calculated and then their reaction mechanisms are discussed in detail. This study provides direct evidence to support the essential role of the O 2-bridged bicyclic compounds in the particle formation from the OH initiated oxidation of 1,3,5-TMB.
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