A crossed molecular beams study on the formation and energetics of the resonantly stabilized free i-C4H3(X A 0) radical and its isotopomers
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چکیده
The chemical dynamics of the formation of the i-C4H3(X A 0) radical together with its partially deuterated isotopomers were investigated in eight crossed molecular beams experiments of dicarbon molecules in their XRg electronic ground and in first excited a Pu state with (partially deuterated) ethylene at collision energies between 12.1 and 40.9 kJ mol . The center-of-mass angular distributions suggest that the reaction dynamics on the singlet and triplet surfaces are indirect and involve butatriene reaction intermediates. In case of the C2/C2H4 reaction, the ‘symmetric’ singlet butatriene intermediate would lead solely to a symmetric center-of-mass angular distribution; however, in combination with isotopically labeled reactants, we deduced that triplet butatriene intermediates excited to B/C like rotations likely account for the observed asymmetries in the center-of-mass angular distributions at higher collision energies. The translational energy distributions are also indicative of the involvement of both the triplet and singlet surfaces which lead both to the i-C4H3(X A 0) radicals through lose (singlet) and tight (triplet) exit transitions states. Also, our experiments helped to determine the enthalpy of formation of the i-C4H3(X A 0) radical to be about 504 ± 10 kJ mol 1 in good agreement with previous computational studies suggesting 498–499 kJ mol . The explicit identification of the resonance-stabilized i-C4H3(X A 0) radical proposes that the reaction of dicarbon with ethylene can lead to formation of i-C4H3(X A 0) in combustion flames; the n-C4H3(X A 0) isomer is not formed in this reaction. This conclusion correlates nicely with Hansen’s et al. flame experiments at the advanced light source observing only the i-C4H3(X A 0) radical in hydrocarbon flames. Published by Elsevier B.V.
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تاریخ انتشار 2007