Prenucleation chemistry of aromatics: A two-ring precursor?

Prenucleation reaction chemistry of polycyclic aromatic hydrocarbons was examined in detailed, site-specific kinetic Monte-Carlo simulations, tracking a single aromatic structure evolving from naphthalene in soot environments of two laminar premixed flames. The numerical results offer a possible reconciliation of a recent flame-based suggestion that one- or two-ring aromatics are the precursors to soot with the otherwise accumulating evidence that soot nucleation begins with mid-size aromatics. The resolution rests in the numerical observation of rapid destruction of the two-ring aromatic molecule, naphthalene, and its replacement with cyclopenta-added derivative structures. The analysis of the reaction events identified important contributions to aromatics evolution from methyl addition to edge five-membered rings. The computed curvature of the growing aromatics exhibited a similar dependence on the molecular size in two substantially different flame environments, thus raising a possibility of universality in aromatic-structure evolution. [ABSTRACT FROM AUTHOR]