Experimental results supported by density functional theory calculations show carbonate formation and reaction on atomic oxygen precovered Au(111). Oxygen mixing is observed in temperature-programmed desorption measurements when a Au (111) precovered with O-16 is exposed to isotopically labeled CO2 ((CO2)-O-18). The presence of 160180 is attributed to surface carbonate formation and decomposition at surface temperatures ranging from 77-400 K and initial oxygen coverages ranging from 0.18-2.1 ML. A reaction probability on the order of 10(-4) and an activation energy of -0.15 +/- 0.08 eV are estimated for this reaction.