Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures

The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry. Here we study this reaction in a high-temperature flow reactor by IR/UV ion dip spectroscopy, using free electron laser radiation as mid-infrared source. We identified several major reaction products based on their infrared spectra, among them indene, 1,2-dihydronaphthalene, naphthalene, biphenyl and para -terphenyl. Due to the structural sensitivity of the method, the reaction products were identified isomer-selectively. The work shows that the formation of indene and naphthalene, which was previously considered to be evidence for the HACA (hydrogen abstraction C 2 H 2 addition) mechanism in the formation of polycyclic aromatic hydrocarbons and soot can also be understood in a phenyl addition model. The self-reaction of the phenyl radical is one of the key reactions in combustion chemistry.