Crossed-beam reaction of carbon atoms with hydrocarbon molecules. II. Chemical dynamics of {ital n}-C{sub 4}H{sub 3} formation from reaction of C({sup 3}{ital P}{sub {ital j}}) with methylacetylene, CH{sub 3}CCH ({ital X}{sup 1}{ital A}{sub 1})
- Department of Chemistry, University of California, Berkeley, California 94720 (United States)
The reaction between ground-state carbon atoms, C({sup 3}{ital P}{sub {ital j}}), and methylacetylene, CH{sub 3}CCH ({ital X}{sup 1}{ital A}{sub 1}), was studied at average collision energies of 20.4 and 33.2 kJmol{sup -1} using the crossed molecular beams technique. Product angular distributions and time-of-flight spectra of C{sub 4}H{sub 3} at {ital m/e}=51 were recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions isotropic at lower, but forward scattered with respect to the carbon beam at a higher collision energy. The translational energy flux distributions peak at 30{endash}60 kJmol{sup {minus}1} and show an average fractional translational energy release of 22-30%. The maximum energy release as well as the angular distributions are consistent with the formation of the {ital n}-C{sub 4}H{sub 3} radical in its electronic ground state. Reaction dynamics inferred from these distributions indicate that the carbon atom attacks the {pi}-orbitals of the methylacetylene molecule via a loose, reactant like transition state located at the centrifugal barrier. The initially formed triplet 1-methylpropendiylidene complex rotates in a plane almost perpendicular to the total angular momentum vector around the {ital B}/{ital C}-axes and undergoes [2,3]-hydrogen migration to triplet 1-methylpropargylene. Within 1-2 ps, the complex decomposes via C-H bond cleavage to {ital n}-C{sub 4}H{sub 3} and atomic hydrogen. The exit transition state is found to be tight and located at least 30-60 kJmol{sup -1} above the products. The explicit identification of the {ital n}-C{sub 4}H{sub 3} radical under single collision conditions represents a further example of a carbon{endash}hydrogen exchange in reactions of ground state carbon atoms with unsaturated hydrocarbons. This channel opens a versatile pathway to synthesize extremely reactive hydrocarbon radicals relevant to combustion processes as well as interstellar chemistry.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 392135
- Journal Information:
- Journal of Chemical Physics, Vol. 105, Issue 19; Other Information: PBD: Nov 1996
- Country of Publication:
- United States
- Language:
- English
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