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Issue 2, 2012
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Chemical dynamics of the CH(X2Π) + C2H4(X1A1g), CH(X2Π) + C2D4(X1A1g), and CD(X2Π) + C2H4(X1A1g) reactions studied under single collision conditions

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Abstract

The crossed beam reactions of the methylidyne radical with ethylene (CH(X2Π) + C2H4(X1A1g)), methylidyne with D4-ethylene (CH(X2Π) + C2D4(X1A1g)), and D1-methylidyne with ethylene (CD(X2Π) + C2H4(X1A1g)) were conducted at nominal collision energies of 17–18 kJ mol−1 to untangle the chemical dynamics involved in the formation of distinct C3H4 isomers methylacetylene (CH3CCH), allene (H2CCCH2), and cyclopropene (c-C3H4) viaC3H5 intermediates. By tracing the atomic hydrogen and deuterium loss pathways, our experimental data suggest indirect scattering dynamics and an initial addition of the (D1)-methylidyne radical to the carbon–carbon double bond of the (D4)-ethylene reactant forming a cyclopropyl radical intermediate (c-C3H5/c-C3D4H/c-C3H4D). The latter was found to ring-open to the allyl radical (H2CCHCH2/D2CCHCD2/H2CCDCH2). This intermediate was found to be long lived with life times of at least five times its rotational period and decomposed via atomic hydrogen/deuterium loss from the central carbon atom (C2) to form allenevia a rather loose exit transition state in an overall strongly exoergic reaction. Based on the experiments with partially deuterated reactants, no compelling evidence could be provided to support the formation of the cyclopropene and methylacetylene isomers under single collision conditions. Likewise, hydrogen/deuterium shifts in the allyl radical intermediates or an initial insertion of the (D1)-methylidyne radical into the carbon–hydrogen/deuterium bond of the (D4)-ethylene reactant were found to be—if at all—of minor importance. Our experiments propose that in hydrocarbon-rich atmospheres of planets and their moons such as Saturn's satellite Titan, the reaction of methylidyne radicals should lead predominantly to the hitherto elusive allene molecule in these reducing environments.

Graphical abstract: Chemical dynamics of the CH(X2Π) + C2H4(X1A1g), CH(X2Π) + C2D4(X1A1g), and CD(X2Π) + C2H4(X1A1g) reactions studied under single collision conditions

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Publication details

The article was received on 19 Jul 2011, accepted on 11 Oct 2011 and first published on 23 Nov 2011


Article type: Paper
DOI: 10.1039/C1CP22350J
Citation: Phys. Chem. Chem. Phys., 2012,14, 529-537
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    Chemical dynamics of the CH(X2Π) + C2H4(X1A1g), CH(X2Π) + C2D4(X1A1g), and CD(X2Π) + C2H4(X1A1g) reactions studied under single collision conditions

    F. Zhang, P. Maksyutenko and R. I. Kaiser, Phys. Chem. Chem. Phys., 2012, 14, 529
    DOI: 10.1039/C1CP22350J

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