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Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures

Taylor, S.E., Goddard, A., Blitz, M.A., Cleary, P.A. and Heard, D.E. (2008) Pulsed Laval nozzle study of the kinetics of OH with unsaturated hydrocarbons at very low temperatures. Physical Chemistry Chemical Physics, 10 (3). pp. 422-437. ISSN 1463-9076

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Abstract

The kinetics of reactions of the OH radical with ethene, ethyne (acetylene), propyne (methyl acetylene) and t-butyl-hydroperoxide were studied at temperatures of 69 and 86 K using laser flash-photolysis combined with laser-induced fluorescence spectroscopy. A new pulsed Laval nozzle apparatus is used to provide the low-temperature thermalised environment at a single density of similar to 4 x 10(16) molecule cm(-3) in N-2. The density and temperature within the flow are determined using measurements of impact pressure and rotational populations from laser-induced fluorescence spectroscopy of NO and OH. For ethene, rate coefficients were determined to be k(2) = (3.22 +/- 0.46) x 10(-11) and (2.12 +/- 0.12) x 10(-11) cm(3) molecule(-1) s(-1) at T = 69 and 86 K, respectively, in good agreement with a master-equation calculation utilising an ab initio surface recently calculated for this reaction by Cleary et al. (P. A. Cleary, M. T. Baeza Romero, M. A. Blitz, D. E. Heard, M. J. Pilling, P. W. Seakins and L. Wang, Phys. Chem. Chem. Phys., 2006, 8, 5633-5642) For ethyne, no previous data exist below 210 K and a single measurement at 69 K was only able to provide an approximate upper limit for the rate coefficient of k(3) < 1 x 10(-12) cm(3) molecule(-1) s (-1), consistent with the presence of a small activation barrier of similar to 5 kJ mol (-1) between the reagents and the OH-C2H2 adduct. For propyne, there are no previous measurements below 253 K, and rate coefficients of k(4) = (5.08 +/- 0.65), (5.02 +/- 1.11) and (3.11 +/- 0.09) x 10(-12) cm(3) molecule(-1) s(-1) were obtained at T = 69, 86 and 299 K, indicating a much weaker temperature dependence than for ethene. The rate coefficient k(1) = (7.8 +/- 2.5) x 10(-11) cm(3) molecule(-1) s (-1) was obtained for the reaction of OH with t-butyl-hydroperoxide at T = 86 K. Studies of the reaction of OH with benzene and toluene yielded complex kinetic profiles of OH which did not allow the extraction of rate coefficients. Uncertainties are quoted at the 95% confidence limit and include systematic errors.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 Royal Society of Chemistry. This is an author produced version of a paper published in Physical Chemistry Chemical Physics. Uploaded in accordance with the publisher's self archiving policy.
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Chemistry (Leeds)
Depositing User: Repository Administrator York
Date Deposited: 08 Apr 2008 16:19
Last Modified: 08 Feb 2013 17:05
Published Version: http://dx.doi.org/10.1039/b711411g
Status: Published
Publisher: Royal Society of Chemistry
Refereed: Yes
Identification Number: 10.1039/b711411g
Related URLs:
URI: http://eprints.whiterose.ac.uk/id/eprint/3723

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