Anomalous isotope effects in the O(1D) + CO2 isotope exchange reaction

The stable isotope compn. of atm. CO_2 can be used to constrain the relative strengths of carbon sources and sinks, and trace the evolution of large-scale atm. transport. In the stratosphere, CO_2 shows an unusual, puzzling enrichment in ^(17)O relative to ^(18)O which is strongly correlated with enrichments in multiply-substituted isotopologues of mass 47 (mainly ^(13)C^(18)O^(16)O). We report evidence of an anomalous enrichment in the multiply-substituted CO_2 isotopologues arising directly from O(1D) + CO_2 isotope exchange reaction. This reaction proceeds through the CO_3* intermediate and these observations may provide information on the dynamics and mechanism of the exchange process. The implications of this for the electronic structure of CO_3*, symmetry-based anomalous isotope effects, and stratosphere-troposphere transport are discussed