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Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments

Abstract : Product detection studies of C(P-3) atom reactions with butene (C4H8) isomers (but-1-ene, cis-but-2-ene, trans-but-2-ene) are carried out in a flow tube reactor at 353 K and 4 Torr under multiple collision conditions. Ground state carbon atoms are generated by 248 nm laser photolysis of tetrabromomethane, CBr4, in a buffer of helium. Thermalized reaction products are detected using synchrotron tunable VUV photoionization and time-of-flight mass spectrometry. The temporal profiles of the detected ions are used to discriminate products from side or secondary reactions. For the C(P-3) + trans-but-2-ene and C(P-3) + cis-but-2-ene reactions, various isomers of C4H5 and C5H7 are identified as reaction products formed via CH3 and H elimination. Assuming equal ionization cross sections for all C4H5 and C5H7 isomers, C4H5:C5H7 branching ratios the C(P-3) + trans-but-2-ene and the C(3P) + cis-but-2-ene reactions, respectively. For the C(P-3) + but-1-ene reaction, two reaction channels are observed: the H-elimination channel, leading to the formation of the ethylpropargyl isomer, and the C3H3 + C2H5 channel. Assuming equal ionization cross sections for ethylpropargyl and C3H3 radicals, a branching ratio of 1:0.95 for the C3H3 + C2H5 and H + ethylpropargyl channels is derived. The experimental results are compared to previous H atom branching ratios and used to propose the most likely mechanisms for the reaction of ground state carbon atoms with butene isomers.
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Jérémy Bourgalais, Michael Spencer, David L. Osborn, Fabien Goulay, Sébastien Le Picard. Reactions of Atomic Carbon with Butene Isomers: Implications for Molecular Growth in Carbon-Rich Environments. Journal of Physical Chemistry A, American Chemical Society, 2016, 120 (46), pp.9138--9150. ⟨10.1021/acs.jpca.6b09785⟩. ⟨hal-01437440⟩

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