Atmos. Chem. Phys. Discuss., 11, 16075-16105, 2011
© Author(s) 2011. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Isotope effects in N2O photolysis from first principles
J. A. Schmidt1, M. S. Johnson1, and R. Schinke2
1Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
2Max-Planck-Institut für Dynamik und Selbstorganisation, 37073 Göttingen, Germany

Abstract. For the first time, accurate potential energy surfaces allow N2O cross sections and isotopic fractionation spectra to be derived that are in agreement with available experimental data (without ad hoc shifting), extending knowledge to a much broader range of conditions. Absorption spectra of rare N- and O-isotopologues (15N14N16O, 14N15N16O, 15N216O, 14N217O and 14N218O) calculated using wavepacket propagation are compared to the most abundant isotopologue (14N216O). The fractionation constants as a function of wavelength and temperature are in excellent agreement with experimental data. The study shows that excitations from the 3rd excited bending state, (0,3,0), and the first combination band, (1,1,0), are important for explaining the isotope effect at wavelengths longer than 210 nm. Only a small amount of the mass independent oxygen isotope anomaly observed in atmospheric N2O samples can be explained as arising from photolysis.

Citation: Schmidt, J. A., Johnson, M. S., and Schinke, R.: Isotope effects in N2O photolysis from first principles, Atmos. Chem. Phys. Discuss., 11, 16075-16105, doi:10.5194/acpd-11-16075-2011, 2011.
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