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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 + HO2, 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 .22±.07, consistent with previous flash photolysis studies.