Effect of HBr, HCl and Cl2 on fullerene formation in benzene/oxygen/argon flames

Amounts between 2.5 and 5.9% of HBr, HCl and Cl-2 were added to fullerene forming benzene/oxygen/argon flat-flames burning at 75 mbar in an attempt to affect halogen substitutions in the carbon framework. The inhibition effect of HBr dramatically reduced the yield of fullerene, while it stayed in the same order of magnitude after addition of HCl or Cl-2. No formation of halogenated fullerenic compounds could be detected by mass spectrometry using chemical ionization with CH4/N2O or MALDI. The measurement of bromine- and chlorine-precursor mass spectra showed the formation of a great number of bromine or chlorine containing compounds, essentially polycyclic aromatic hydrocarbons (PAH). In the case of HBr addition, only relatively small molecules could be observed because reactions with bromine atoms are thermodynamically less favourable in regions far from the burner with relatively high temperatures.