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Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO_2 Radicals

Morajkar, Pranay and Schoemaecker, Coralie and Okumura, Mitchio and Fittschen, Christa (2014) Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO_2 Radicals. International Journal of Chemical Kinetics, 46 (5). pp. 245-259. ISSN 0538-8066. doi:10.1002/kin.20817.

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Rate and equilibrium constants for the reaction of HO_2 with formaldehyde CH_2O + HO_2 ↔ HOCH_2O_2 and acetaldehyde CH_3CHO + HO_2 ↔ CH_3CH(OH)O_2 have been directly measured. The concentration of HO_2 radicals was followed in a time-resolved method by coupling cw-CRDS (cavity ringdown spectroscopy) to laser photolysis. The reaction of HO_2 with CH_2O (R1) was measured at 50 Torr helium over the temperature range 292–306 K, whereas the reaction of CH_3CHO with HO_2 (R2) was measured in 50 Torr He but at only 294 K. The observed HO_2 decay profiles were modeled to take into account secondary chemistry, especially that of the reaction products, hydroxyl-peroxy radical adducts. The rate constants for forward and back reactions of (R1) at 297 K were found to be k_1 = (3.3 ± 0.6) × 10^(−14) cm^3 molecule^(−1)s^(−1) and k_(−1) = (55 ± 5) s^(−1), respectively, both roughly a factor of two slower than earlier measurements (possibly due to falloff effects), while the equilibrium constant was found to be K_1 = (6.0 ± 1.8) × 10^(−16) molecule^(−1) cm^3 at 297 K, in good agreement with earlier, more indirect determinations. The equilibrium constant of the reaction with CH_3CHO was found to be K_2 = (1.7 ± 0.5) × 10^(−17) molecule^(−1) cm^3 at 294 K, with the forward rate constant k_2 = (1.5 ± 0.75) × 10^(−14) cm^3 molecule^(−1)s^(−1) and the rate constant for the back reaction k_(−2) = (900 ± 450)s^(−1).

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Okumura, Mitchio0000-0001-6874-1137
Additional Information:© 2013 Wiley Periodicals, Inc. Issue published online: 27 MAR 2014; Article first published online: 23 SEP 2013; Manuscript Accepted: 1 AUG 2013; Manuscript Revised: 31 JUL 2013; Manuscript Received: 15 JUN 2013. The laboratory participates in the Institut de Recherche en ENvironnement Industriel (IRENI), which is financed by RégionNord Pas-de-Calais, the Ministère de l'Enseignement Supérieur et de la Recherche, the CNRS, and European Regional Development Fund (ERDF). This project was supported by the French ANR agency under contract no. ANR−11-LabEx-0005–01 CaPPA (Chemical and Physical Properties of the Atmosphere) and by the CNRS through the French–German program “ATMOCHEM.” MO acknowledges support of the Upper Atmospheric Research Program (UARP) of the U.S. National Aeronautics and Space Administration (NASA) for grant NNX12AE01G, and IRENI for a visiting professorship.
Funding AgencyGrant Number
Agence Nationale pour la Recherche (ANR)ANR-11-Lab-Ex-0005-01 CaPPA
Centre National de la Recherche Scientifique (CNRS)UNSPECIFIED
Institut de Recherche en Environnement IndustrielUNSPECIFIED
Issue or Number:5
Record Number:CaltechAUTHORS:20140425-103708205
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Official Citation:Morajkar, P., Schoemaecker, C., Okumura, M. and Fittschen, C. (2014), Direct Measurement of the Equilibrium Constants of the Reaction of Formaldehyde and Acetaldehyde with HO2 Radicals. Int. J. Chem. Kinet., 46: 245–259. doi: 10.1002/kin.20817
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:45227
Deposited By: Aucoeur Ngo
Deposited On:25 Apr 2014 19:15
Last Modified:10 Nov 2021 17:01

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