New aspects of growth mechanisms for polycyclic aromatic hydrocarbons in diffusion flames

Two-photon ionization time-of-flight mass spectroscopy is used to analyze combustion products from laminar methane diffusion flames. High-resolution height profiles in the symmetry axis of the flame show sensitively the rise and decay of concentrations of various polycyclic aromatic hydrocarbons (PAH) in the mass range up to 472 amu. From a comparison of these profiles in dependence of the carbon content of the PAH, we derive fingerprints both of successive acetylene addition and of reactive coagulation as growth mechanisms of PAH.