Neutral-neutral Reactions in the Interstellar Medium. I. Formation of Carbon Hydride Radicals via Reaction of Carbon Atoms with Unsaturated Hydrocarbons
نویسندگان
چکیده
The reactions of ground-state atomic carbon with acetylene, (1), methylacetylene, (2), 22 3 ethylene, (3), and propylene, (4), are investigated at relative collision energies between 8.8 24 36 and 45 kJ mol~1 in crossed-beam experiments to elucidate the reaction products and chemical dynamics of atom-neutral encounters relevant to the formation of carbon-bearing molecules in the interstellar medium (ISM). Reactive scattering signal is found for (1), as well as the hitherto unobserved inter3 stellar radicals (2), (3), and (4). All reactions proceed on the triplet surface via addition 43 33 45 of the carbon atom to the molecular n-bond. The initial collision complexes undergo hydrogen migration (1/2) or ring opening (3/4) and decompose via C-H-bond rupture to (1), (2), pro3 43 pargyl (3), and methylpropargyl (4). The explicit identiÐcation of the carbon-hydrogen exchange channel under single collision conditions identiÐes this class of reaction as a potential pathway to carbon-bearing species in the ISM. Especially, the formation of correlates with actual astronomical observations 3 and explains a higher [cratio in the dark cloud TMC-1 as compared to the carbon star 33 IRC ]10216. Our Ðndings strongly demand the incorporation of distinct structural isomers in prospective chemical models of interstellar clouds, hot cores, and circumstellar envelopes around carbon stars. Subject headings : ISM: molecules È methods : laboratory È molecular processes
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