Carbonaceous Nanoparticle Molecular Inception from Radical Addition and van der Waals Coagulation of Polycyclic Aromatic Hydrocarbon-Based Systems. A Theoretical Study

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. Soot particle inception, with transition of relatively low-mass molecular systems from the gaseous phase to a solid nature through coagulation/condensation, is believed to take place via chemical reactions as well as van der Waals (vdW) interactions involving polycyclic aromatic hydrocarbons (PAHs) or derivatives. In this Article, radical addition between open and closed shell molecular PAH or PAH-like systems (R• + P → R–P•) is examined by density functional theory, and different σ bond formations are compared to the stacking of the aromatic components (R•:P, previously discussed in J. Phys. Chem. C2011, 115, 1732–1739). Energetic and entropic effects are examined. At higher T, formation of aliphatic bridges (hence reticulation) appears to be of the utmost importance to link PAH-like moieties, with a preference for more extend...