1Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark
2Max-Planck-Institut für Dynamik und Selbstorganisation, 37073 Göttingen, Germany
Received: 20 May 2011 – Published in Atmos. Chem. Phys. Discuss.: 26 May 2011
Abstract. For the first time, accurate first principles potential energy surfaces allow N2O cross sections and isotopic fractionation spectra to be derived that are in agreement with all available experimental data, extending our 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 state, (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.
Revised: 23 Aug 2011 – Accepted: 24 Aug 2011 – Published: 02 Sep 2011
Schmidt, J. A., Johnson, M. S., and Schinke, R.: Isotope effects in N2O photolysis from first principles, Atmos. Chem. Phys., 11, 8965-8975, doi:10.5194/acp-11-8965-2011, 2011.