Thumbnail
Access Restriction
Open

Author Kaiser, R. I. ♦ Stranges, D. ♦ Lee, Y. T. ♦ Suits, A. G.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword PHYSICS ♦ ACETYLENE ♦ ATOM-MOLECULE COLLISIONS ♦ CARBON ♦ COLLIDING BEAMS ♦ MOLECULAR BEAMS ♦ TIME-OF-FLIGHT METHOD ♦ MASS SPECTROSCOPY ♦ ANGULAR DISTRIBUTION ♦ CHEMICAL REACTION KINETICS ♦ HYDROCARBONS
Abstract 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.
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 1996-11-01
Publisher Department Lawrence Berkeley National Laboratory
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 105
Issue Number 19
Organization Lawrence Berkeley National Laboratory


Open content in new tab

   Open content in new tab