Infrared analysis of flame-generated PAH samples

Data from infrared analyses are presented on the functional groups present in dichloromethane-soluble polycyclic aromatic hydrocarbon (PAH) material sampled from sooting flames as a function of height above the burner. The trends in the data indicate that PAH become progressively more aromatic (and less aliphatic) in nature as they grow up to the point of soot nucleation. At the soot nucleation point, the aromatic-to-aliphatic ratio drops dramatically. These changes are occurring in a zone of the flame in which the temperature is rapidly rising. A hypothesis is presented in which the cleavage of aliphatic groups or loss of aliphatic hydrogens from PAH coincides with the reactive coagulation of PAH to form soot nuclei.