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Published October 8, 2004 | Published
Journal Article Open

Evidence for O-atom exchange in the O(^1D) + N_2O reaction as the source of mass-independent isotopic fractionation in atmospheric N_2O


Recent experiments have shown that in the oxygen isotopic exchange reaction for O(^1D) + CO_2 the elastic channel is approximately 50% that of the inelastic channel [Perri et al., 2003]. We propose an analogous oxygen atom exchange reaction for the isoelectronic O(^1D) + N_2O system to explain the mass-independent isotopic fractionation (MIF) in atmospheric N_2O. We apply quantum chemical methods to compute the energetics of the potential energy surfaces on which the O(^1D) + N_2O reaction occurs. Preliminary modeling results indicate that oxygen isotopic exchange via O(^1D) + N_2O can account for the MIF oxygen anomaly if the oxygen atom isotopic exchange rate is 30–50% that of the total rate for the reactive channels.

Additional Information

© 2004 by the American Geophysical Union. Received 7 July 2004; revised 21 August 2004; accepted 31 August 2004; published 8 October 2004. We thank R.-L. Shia for helping to run the 2-D model for N_2O and M. Gerstell, X. Jiang, and J. Kaiser for helpful discussions. We also thank the two referees for helpful comments. Special thanks are due M. H. Thiemens for sending us his data and for many illuminating conversations. This work was supported in part by NSF grant ATM-9903790. The extension of the Caltech/JPL 2-D model to the troposphere was supported by NASA ACMAP grant NAG1-1806. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract No. DE-AC04-94AL85000. RPM would like to thank Schrodinger, LLC, for use of the Jaguar program.

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