The O-18(D-1)+(CO2)-C-44 oxygen isotope exchange reaction has been studied using a crossed molecular beam apparatus at a collision energy of 7.7 kcal/mol. Two different reaction channels are observed, both proceeding via a relatively long-lived CO3 complex. Electronic quenching of O(D-1) is the major channel, accounting for 68% of all isotope exchange, while 32% occurs without quenching. These results are the first experimental evidence that isotope exchange can occur through a long-lived CO3 intermediate without subsequent crossing to the triplet surface, and could prove important for atmospheric models of oxygen isotope exchange between CO2 and O-3. (C) 2003 American Institute of Physics.