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The Decomposition of 2-Pentyl and 3-Pentyl Radicals



Jeffrey A. Manion, Iftikhar A. Awan


The isomerization and decomposition reactions of 2-pentyl and 3-pentyl radicals have been studied in a single-pulse shock tube over a temperature range of 973 K to 1121 K and pressures of 120 kPa to 800 kPa. The results represent the first direct study of the alkene product branching ratio resulting from the kinetics of the competition between isomerization and beta C-C bond scission for a secondary alkyl radical at high temperatures. Such species are representative of intermediates important in the combustion of typical hydrocarbon fuels. In the present work small quantities (μL/L levels) of H atoms are thermally produced in the presence of excess (E)-2-pentene and lead to the radicals of interest via addition of H to the double bond. Decomposition of the chemically activated pentyl radicals results in the stable olefin products ethene, propene, and 1-butene, which are detected in postshock gas chromatographic analyses utilizing flame-ionization and mass-spectrometric detection. It is shown that the olefin product ratios can be related to the isomerization and decomposition reactions of the 2-pentyl and 3-pentyl radicals and the results are consistent with the existence of distinct non-overlapping cracking patterns for the two radicals. The data are compared with predictions made on the basis of a model developed from experiments on the decomposition of thermalized (i.e. not chemically activated) 1-pentyl radicals. Good agreement is observed. In conjunction with an RRKM/Master Equation analysis, the results for 2-pentyl and 3-pentyl radicals are projected over a wide range of temperatures. In addition, the rate constants for addition of H atoms to the alternate double bond positions of (E)-2-pentene are derived relative to a standard reaction and absolute rate constants for these processes are reported.
Proceedings of the Combustion Institute


2-pentyl, 3-pentyl, kinetics, H-atoms, 2-pentene


Manion, J. and Awan, I. (2012), The Decomposition of 2-Pentyl and 3-Pentyl Radicals, Proceedings of the Combustion Institute, [online], (Accessed April 15, 2024)
Created July 15, 2012, Updated February 19, 2017