Theoretical Investigation of the Reaction of Pyrene\nFormation from Fluoranthene

This\npaper has investigated the reaction process concerning pyrene\nformation from fluoranthene in their electronic ground states. Both\naromatic compounds are considered as direct soot precursors. The geometrical\nparameters, the vibrational frequencies, and the zero-point energies\nhave been calculated using the BMK (Boese–Martin for kinetics)\nmethod and the 6-311++G­(d,p) basis set. More accurate single-point\nenergies have been obtained using BMK/6-311++G­(3df,2p) to retrieve\nthermodynamic properties (ΔrH°(T) and ΔrG°(T)) over a wide temperature range (298–2500 K). The\nisomerization reaction of fluoranthene to pyrene is exothermic and\nspontaneous in standard conditions. The transition states and the\npossible intermediate species have been located on the singlet potential\nenergy surface in order to determine the reaction mechanism. Two different\nreaction channels have been investigated and characterized by entrance\nreaction barriers of about 419 and 771 kJ mol–1 for\nthe first and the second reaction pathways, respectively. The present\nwork demonstrates that the first reaction channel is the most energetically\nfavored pathway at high temperatures. Therefore, the kinetic parameters\nof the forward and reverse first step reactions have been determined\nin sooting flame conditions.