Crossed-beam Reaction of Carbon Atoms with Hydrocarbon Molecules IV: Chemical Dynamics of Methylpropargyl Radical Formation, C4H5, from Reaction of C(3Pj) with propylene, C3H6 (1XA’).

The reaction between ground state carbon atoms and propylene, C3H6 , was studied at average collision energies of 23.3 and 45.0 kJ mol21 using the crossed molecular beam technique. Product angular distributions and time-of-flight spectra of C4H5 at m/e553 were recorded. Forwardconvolution fitting of the data yields a maximum energy release as well as angular distributions consistent with the formation of methylpropargyl radicals. Reaction dynamics inferred from the experimental results suggest that the reaction proceeds on the lowest 3A surface via an initial addition of the carbon atom to the p-orbital to form a triplet methylcyclopropylidene collision complex followed by ring opening to triplet 1,2-butadiene. Within 0.3–0.6 ps, 1,2-butadiene decomposes through carbon–hydrogen bond rupture to atomic hydrogen and methylpropargyl radicals. The explicit identification of C4H5 under single collision conditions represents a further example of a carbon–hydrogen exchange in reactions of ground state carbon with unsaturated hydrocarbons. This versatile machine represents an alternative pathway to build up unsaturated hydrocarbon chains in combustion processes, chemical vapor deposition, and in the interstellar medium.