Pressure Effects on Product Channels of the Allyl Radical Reactions; C3H5+C3H5 and C3H5+CH3

Details Pressure Effects on Product Channels of the Allyl Radical Reactions; C3H5+C3H5 and C3H5+CH3 Pressure Effects on Product Channels of the Allyl Radical Reactions; C3H5+C3H5 and C3H5+CH3

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p13a1645h&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P13A-1645

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[5405] Planetary Sciences: Solid Surface Planets / Atmospheres, [5704] Planetary Sciences: Fluid Planets / Atmospheres, [6005] Planetary Sciences: Comets And Small Bodies / Atmospheres, [6281] Planetary Sciences: Solar System Objects / Titan

Scientific paper

Relatively large hydrocarbon molecules (C4, C6 and larger) have been detected in several planetary environments. The mechanism for the formation of such large molecular species and detailed mechanism for their potential destruction are not well understood and are of considerable current interest. Previously we have studied the kinetics and product channels of small unsaturated hydrocarbon radical (C2 and C3s) reactions relevant to planetary atmospheric modeling. Reactions of C2 radicals (such as vinyl, H2CCH and ethynyl C2H) and C3 radicals (such as propargyl, HCCCH2) can affect the abundances of a large number of stable observable C3, C4, C5, C6 and larger molecules, including linear, aromatic and even poly aromatic molecules. Pressure-dependent product yields have been determined experimentally for the self- and cross-radical reactions performed at 298 K and at pressures between ~4 Torr (0.5 kPa) and 760 Torr (101 kPa). Final reaction products were quantitatively determined using a gas chromatograph with mass spectrometry/flame ionization detection (GC/MS/FID). In some cases complementary computational studies extended the pressure and temperature range of the experiments and provided valuable information on the complex reaction mechanisms. Theses studies provide a systematic framework so that important energetic and structural parameters for radical-radical reactions can be assessed. Here we report recent results for the allyl radical reactions H2CCCH3+ H2CCCH3 and H2CCCH3+CH3. For the allyl radical self-reaction, at high pressures the "head -to-head", combination channel forming 1,5-hexadiene is dominant with a combination/disproportionation = 1,5-hexadiene/propyne ratio of about 24 at 500 Torr (67 kPa, T=298K). At low pressures the ratio is substantially reduced to about 1.2 (at 0.3 kPa) and other major products are observed including allene, propene, 1-butene and propyne.

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