The first multi-isotope (Δ17O and Δ18O) study of an isotopic exchange between an electronically excited species O( 1D) and CO2 has been performed. The O( 1D), which was generated from O3 UV photolysis, undergoes an isotopic exchange with CO2 via a CO3* intermediate transition state. A non-mass-dependent isotopic effect is observed via the exchange, which has a direct application to recent stratospheric CO2 observations and analysis of water presumed to be derived from the Martian surface. The isotopic data are also important in assessing the physical-chemical properties of the CO3* complex. ¿ American Geophysical Union 1992