CO + OH → CO2 + H: The relative reaction rate of five CO isotopologues

Karen L. Feilberg; Stig R. Sellevåg; Claus J. Nielsen; David W. T. Griffith; Matthew S. Johnson

doi:10.1039/B204827M

CO + OH → CO₂ + H: The relative reaction rate of five CO isotopologues

Karen L. Feilberg,*^a Stig R. Sellevåg,^b Claus J. Nielsen,^b David W. T. Griffith^c and Matthew S. Johnson^a

* Corresponding authors

^a Department of Chemistry, University of Copenhagen, Universitetsparken 5, Copenhagen Ø, Denmark
E-mail: klf@kiku.dk

^b Department of Chemistry, University of Oslo, P.O. Box 1033, Blindern, Oslo, Norway

^c Department of Chemistry, University of Wollongong, Wollongong, Australia

Abstract

The reaction of carbon monoxide with the hydroxyl radical (CO + OH) plays a central role in tropospheric chemistry. While the analysis of stable isotope enrichment has been used to refine models of the sources and sinks of atmospheric CO and CO₂, less is known about the mechanism behind the enrichment. We have initiated the present work to provide a larger set of experimental observations of the effect. We report the OH radical reaction rate of ¹²C¹⁶O relative to ¹³C¹⁶O, ¹²C¹⁸O and ¹³C¹⁸O and the reaction rate of ¹²C¹⁷O relative to ¹²C¹⁸O at 295 K. At 1013 mbar the relative rates are 0.960 ± 0.014, 0.943 ± 0.019, 0.948 ± 0.024 and 0.996 ± 0.0067 respectively (k_light/k_heavy, 2σ errors indicated); results at 506 and 66 mbar are also reported. The hydroxyl radical was generated by the UV photolysis of ozone in the presence of water. The concentration of the carbon monoxide isotopologues as a function of photolysis time was determined using a global fit of the rovibrationally resolved FTIR spectrum of the gas mixture in the reaction cell. The observed inverse kinetic isotope effect is best understood in terms of the effect of isotopic substitution on the relative rate of unimolecular dissociation of the HOCO intermediate to reform reagents versus dissociation to products.

Article information

https://doi.org/10.1039/B204827M

Article type

Paper

Submitted

17 May 2002

Accepted

24 Jul 2002

First published

23 Aug 2002

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Phys. Chem. Chem. Phys., 2002,4, 4687-4693

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CO + OH → CO₂ + H: The relative reaction rate of five CO isotopologues

K. L. Feilberg, S. R. Sellevåg, C. J. Nielsen, D. W. T. Griffith and M. S. Johnson, Phys. Chem. Chem. Phys., 2002, 4, 4687 DOI: 10.1039/B204827M

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Physical Chemistry Chemical Physics

CO + OH → CO₂ + H: The relative reaction rate of five CO isotopologues

Abstract

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CO + OH → CO₂ + H: The relative reaction rate of five CO isotopologues

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