Unimolecular Reactions of Peroxy Radicals in Atmospheric Chemistry and Combustion

Peroxy radicals can undergo isomerisation and dissociation reactions in competition with reactions with NO and with other peroxy radicals. Such a competition is central to the recently proposed mechanism for OH regeneration in the atmospheric oxidation of isoprene. The occurrence of peroxy radical isomerisation reactions in both combustion and atmospheric chemistry is discussed, and exemplified by reference to the peroxy radicals formed from the C2H5, CH3CO, HO- C2H2 and HO- C6H6 radicals. The discussion is based on the use of electronic structure and master equation calculations to interpret experimental results.