Accretion product formation in the self-reaction of ethene-derived hydroxy peroxy radicals

In this study we revisit one of the simplest RO₂• + RO₂• reactions: the self-reaction of the ethene-derived hydroxyperoxy radical formed via sequential addition of •OH and O₂ to ethene. Previous studies of this reaction suggested that the branching to 'accretion products', compounds containing the carbon backbone of both reactants, was minimal. Here, CF₃O⁻ GC-CIMS is used to quantify the yields of ethylene glycol, glycolaldehyde, a hydroxy hydroperoxide produced from RO₂• + RO₂•, and a C₄O₄H₁₀ accretion product. These experiments were performed in an environmental chamber at 993 hPa and 294 K. We provide evidence that the accretion product is likely dihydroxy diethyl peroxide (HOC₂H₄OOC₂H₄OH=ROOR) and forms in the gas-phase with a branching fraction of 23 ± 5%. We suggest a new channel in the RO₂• + RO₂• chemistry leading directly to the formation of HO₂ (together with glycolaldehyde and an alkoxy radical). Finally, by varying the ratio of the formation rate of RO₂ and HO₂ in our chamber, we constrain the ratio of the rate coefficient for the reaction of RO₂• + RO₂• to that of RO₂• + HO₂• and find that this ratio is 0.22 ± 0.07, consistent with previous flash photolysis studies.