A crossed molecular beam study of the phenyl radical reaction with 1,3-butadiene and its deuterated isotopologues.

The reactions between the phenyl radical (C(6)H(5)) and 1,3-butadiene (CH(2)CHCHCH(2)) together with its D6- and D4-isotopologues were studied under single collision conditions. The scattering data suggest that the reaction proceeds via indirect scattering dynamics and is initiated by an addition of the phenyl radical to the terminal carbon atom of the 1,3-butadiene molecule to form a C(6)H(5)CH(2)CHCHCH(2) intermediate. Then, the collision complex undergoes a hydrogen atom loss through a tight exit transition state to form the 1-phenyl-1,3-butadiene product. Reactions with isotopically labeled reactants verify experimentally that the hydrogen loss originates from the terminal carbon atom of the 1,3-butadiene reactant. Our results are also compared with other phenyl radical reactions with unsaturated hydrocarbons studied earlier in our laboratory.