Five vs Six Membered-Ring PAH Products from Reaction of o- Methylphenyl Radical and two C3H4 Isomers

Using VUV synchrotron photoionization mass spectrometry, quantum chemistry and RRKM kinetic modeling, our paper identifies the products formed when a substituted aromatic free radical (ortho- methylphenyl) reacts with two C3H4 isomers found in flames – propyne and allene. Both reactions form polycyclic aromatic hydrocarbons but profound structural differences result from the nature of the C3H4 isomer. The allene case favors the formation of six-six bicyclic rings (graphitic), while the formation of new five-six membered bicylics dominate for the propyne case. These conclusions are rigorously supported by experiments, calculations and kinetic modelling.