On the formation of phenyldiacetylene (C6H5CCCCH) and D5-phenyldiacetylene (C6D5CCCCH) studied under single collision conditions

Abstract

The crossed molecular beam reactions of the phenyl and D5-phenyl radical with diacetylene (C₄H₂) was studied under single collision conditions at a collision energy of 46 kJ mol⁻¹. The chemical dynamics were found to be indirect and initiated by an addition of the phenyl/D5-phenyl radical with its radical center to the C1-carbon atom of the diacetylene reactant. This process involved an entrance barrier of 4 kJ mol⁻¹ and lead to a long lived, bound doublet radical intermediate. The latter emitted a hydrogen atom directly or after a few isomerization steps via tight exit transition states placed 20–21 kJ mol⁻¹ above the separated phenyldiacetylene (C₆H₅CCCCH) plus atomic hydrogen products. The overall reaction was determined to be exoergic by about 49 ± 26 kJ mol⁻¹ and 44 ± 10 kJ mol⁻¹ as determined experimentally and computationally, thus representing a feasible pathway to the formation of the phenyldiacetylene molecule in combustion flames of hydrocarbon fuel.