Selective deuteration as a tool for resolving autoxidation mechanisms in α-pinene ozonolysis

• Published in: Atmospheric chemistry and physics 2023-04, Vol.23 (7), p.4373
• Main Authors: Meder, Melissa, Peräkylä, Otso, Varelas, Jonathan G, Luo, Jingyi, Cai, Runlong, Zhang, Yanjun, Kurtén, Theo, Riva, Matthieu, Rissanen, Matti, Geiger, Franz M, Thomson, Regan J, Ehn, Mikael
• Format: Article
• Language: English
• Subjects: Hydrogen; Isomerization; Mass spectrometry
• ISSN: 1680-7316

Highly oxygenated organic molecules (HOMs) from α-pinene ozonolysis have been shown to be significant contributors to secondary organic aerosol (SOA), yet our mechanistic understanding of how the peroxy-radical-driven autoxidation leads to their formation in this system is still limited. The involved isomerisation reactions such as H-atom abstractions followed by O.sub.2 additions can take place on sub-second timescales in short-lived intermediates, making the process challenging to study. Similarly, while the end-products and sometimes radical intermediates can be observed using mass spectrometry, their structures remain elusive. Therefore, we propose a method utilising selective deuterations for unveiling the mechanisms of autoxidation, where the HOM products can be used to infer which C atoms have taken part in the isomerisation reactions. This relies on the fact that if a C-D bond is broken due to an abstraction by a peroxy group forming a -OOD hydroperoxide, the D atom will become labile and able to be exchanged with a hydrogen atom in water vapour (H.sub.2 O), effectively leading to loss of the D atom from the molecule.