Reflection absorption infrared spectroscopy was used to study the reaction of adsorbed molecular oxygen with carbon monoxide to produce adsorbed carbon dioxide at 130 K. By simultaneously monitoring the O-O stretch of O-2(ads), the C-O stretch of CO(ads), and the asymmetric O-C-O stretch of CO2(ads), it is found that there is an O-2-CO interaction, suggesting that the transition state involves direct transfer of an O atom from O-2(ads) to CO, rather than through reaction of CO(ads) with a hot surface O atom produced from O-2 dissociation. (C) 2014 Elsevier B. V. All rights reserved.