title: Ab initio study of nitrogen and position-specific oxygen kinetic isotope effects in the NO + O3reaction.
abstract: Ab initio calculations have been carried out to investigate nitrogen (k15/k14) and position-specific oxygen (k17/k16O & k18/k16) kinetic isotope effects (KIEs) for the reaction between NO and O3using CCSD(T)/6-31G(d) and CCSD(T)/6-311G(d) derived frequencies in the complete Bigeleisen equations. Isotopic enrichment factors are calculated to be -6.7‰, -1.3‰, -44.7‰, -14.1‰, and -0.3‰ at 298 K for the reactions involving the15N16O,14N18O,18O16O16O,16O18O16O, and16O16O18O isotopologues relative to the 14N16O and 16O3isotopologues, respectively (CCSD(T)/6-311G(d)). Using our oxygen position-specific KIEs, a kinetic model was constructed using Kintecus, which estimates the overall isotopic enrichment factors associated with unreacted O3and the oxygen transferred to NO2to be -19.6‰  and -22.8‰, respectively, (CCSD(T)/6-311G(d)) which tends to be in agreement with previously reported experimental data. While this result may be fortuitous, this agreement suggests that our model is capturing the most important features of the underlying physics of the KIE associated with this reaction (i.e., shifts in zero-point energies). The calculated KIEs will useful in future NOxisotopic modeling studies aimed at understanding the processes responsible for the observed tropospheric isotopic variations of NOxas well as for tropospheric nitrate.
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Wendell W
authors.initials: WW
authors.lastname: Walters
authors.affiliation: Department of Earth, Atmospheric, and Planetary Sciences Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Greg
authors.initials: G
authors.lastname: Michalski