Oxygen anion radicals O- play an important role in various physico-chemical processes, including those taking place on solid surfaces, where their behavior is especially difficult to follow. This work presents a detailed study on the behavior of O- radicals adsorbed on FeZSM-5 surface in the reaction of O-2 isotopic exchange carried out over a wide range of temperatures (198-513 K). High concentration of O-in this unique system (called alpha-oxygen) made it possible to identify two exchange mechanisms, R-0 and R-1, operating in the presence of O-alpha. The R-1 mechanism (E = 15 kJ/mol) dominates in the high-temperature region and can be represented by the following equation: O-18(2) + O-16(alpha)- reversible arrow[O-3(-)](alpha) reversible arrow (OO)-O-16-O-18 + O-18(alpha)-. This mechanism is convincingly supported by several arguments: the first order reaction with respect to O-2; the linear dependence of reaction rate on O-alpha concentration: the ESR observation of O-3(-) species (in other systems); and, according to isotopic exchange theory, by a twofold excess of the rate of homoexchange over the rate of heteroexchange. The R-0 exchange (E = 0.8 kJ/mol) is a new reaction pathway that appears at cryogenic temperatures and leads to isotope redistribution only between O-2 molecules, not affecting the isotopic composition of O-alpha This exchange mechanism is not quite clear. The necessity of the presence of O-alpha without its direct involvement in the exchange process seems to be quite surprising. The reaction may proceed via a hypothetical complex [O-5(-)](alpha) which allows cleavage and redistribution of chemical bonds between two O-2 molecules adsorbed on the alpha-oxygen. The cleavage and redistribution of such strong bonds at cryogenic temperatures with nearly zero activation energy are an intriguing phenomenon worthy of further study. (C) 2009 Elsevier Inc. All rights reserved.