Reaction between Peroxy and Alkoxy Radicals Can Form Stable Adducts

Peroxy (RO₂) and alkoxy (RO) radicals are prototypical intermediates in any hydrocarbon oxidation. In this work, we use computational methods to (1) study the mechanism and kinetics of the RO₂ + OH reaction for previously unexplored "R" structures (R = CH(O)CH₂ and R = CH₃C(O)) and (2) investigate a hitherto unaccounted channel of molecular growth, R'O₂ + RO. On the singlet surface, these reactions rapidly form ROOOH and R'OOOR adducts, respectively. The former decomposes to RO + HO₂ and R(O)OH + O₂ products, while the main decomposition channel for the latter is back to the reactant radicals. Decomposition rates of R'OOOR adducts varied between 103 and 0.015 s^-1 at 298 K and 1 atm. The most long-lived R'OOOR adducts likely account for some fraction of the elemental compositions detected in the atmosphere that are commonly assigned to stable covalently bound dimers.