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 C(2)H(5), CH(3)CO, HO-C(2)H(2) and HO-C(6)H(6) radicals. The discussion is based on the use of electronic structure and master equation calculations to interpret experimental results.