A theoretical study of the potential energy surface for the isomerization reaction of fluoranthene to aceanthrylene: Implications for combustion chemistry

Abstract Isomerization reaction of fluoranthene forming aceanthrylene was investigated using density functional theory (DFT). Geometrical structures and scaled vibrational frequencies of all species and thermodynamic properties including standard reaction enthalpies ΔrH°(T) and Gibbs free energies ΔrG°(T) were calculated at a wide range of temperature from 298 to 2500 K at the B97D3/6-311++G(3df,2p)//B97D3/6-311++G(d,p) level of theory. Consequently, the fluoranthene isomerization is initiated via two pathways, either by hydrogen 1,2-shift or carbon 1,2-shift reactions with reaction barrier of 356.6 and 393.6 kJ mol-1. Also, the co-existence of aceanthrylene and acephenanthrylene was observed with the corresponding ΔrH°(0 K) of 28.5 and 53.7 kJ mol-1. Kinetic calculations for the initiative step confirm that in comparison with the carbon 1,2-shift mechanism the hydrogen 1,2-shift mechanism is always predominant. However, as shown by the kinetic calculations, these reactions are not relevant under flame conditions. It may need to find other reaction pathways explaining the conversion of these two intermediate species to pyrene.