On the Mechanism of Soot Nucleation. III. The Fate and Facility of the E-Bridge

Rotationally excited dimerization of aromatic moieties is a mechanism proposed recently to explain the initial steps of soot particle inception in combustion and pyrolysis of hydrocarbons. The product of such dimerization, termed E-bridge, is an angled molecular structure composed of two aromatic rings sharing a common bond. The present study explores the immediate fate of the E-bridge. The performed theoretical analysis indicates that abstraction of a bridge H atom by a gaseous H leads to a rapid transformation of the angled to planar structure. The implications of this result is that the collisionally activated E-bridge formation followed by its flattening effectively increases the size of planar aromatic precursors by combining two aromatic moieties with essentially collisional rates, instead of a slower atom-by-atom buildup. The faster growth speeds up PAH reaching a size when physical dimerization takes over. The dimerization can be further assisted by the biradicaloid valence structure of the flattened E-bridge.

Automated summary

Rotationally excited dimerization of aromatic moieties is proposed as a mechanism for soot particle inception, where the formed E-bridge can rapidly transform from an angled to a planar structure through bridge H atom abstraction. This process effectively speeds up the growth of polycyclic aromatic hydrocarbons by combining aromatic moieties collisionally, leading to physical dimerization.