Theoretical Investigation of Soot Nanoparticle Inception via Polycyclic Aromatic Hydrocarbon Coagulation (Condensation): Energetic, Structural, and Electronic Features

Abstract

Carbon nanoparticles, generated during combustion at relatively low [O2], or under pyrolysis conditions, can be seen both as soot precursors and as primary pollutants in themselves, since they are also directly emitted in the troposphere by vehicles. Soot particle inception (transition of relatively low-mass molecular systems from the gaseous phase to a solid nature) occurs at least in part via polycyclic aromatic hydrocarbon (PAH) coagulation/condensation. Complexes of different PAH systems, bound only by dispersion/multipolar forces, are investigated here by density functional theory, and their structural and energetic features discussed. The energetic features of the complexes allow to define an interplane interaction energy per C atom which compares satisfactorily with published experimental data on graphite exfoliation (i.e., removal of a single layer from the top of its bulk). The temperature dependence of the equilibrium K for these systems is then calculated to estimate the importance of PAH coagu...