Read this ‘HOT’ article by Ian Sims and colleagues:
Low temperature kinetics: the association of OH radicals with O2
Meryem Tizniti, Sébastien D. Le Picard, André Canosa, Ian R. Sims and Ian W. M. Smith
Phys. Chem. Chem. Phys., 2010,DOI: 10.1039/C0CP00591F
Rate constants have been measured at low temperatures for the association of OH radicals with O2 to form the weakly bound hydroxyl-peroxy radical HOOO.