Quantum mechanical study of molecular weight growth process by combinationof aromatic molecules

Formation pathways for high-molecular-mass compound growth are presented, s howing why reactions between aromatic moieties are needed to explain recent experimental findings. These reactions are then analyzed by using quantum mechanical density functional methods. A sequence of chemical reactions bet ween aromatic compounds (e.g., phenyl) and compounds containing conjugated double bonds (e.g., acenaphthylene) was studied in detail. The sequence beg ins with the H-abstraction from acenaphthylene to produce the corresponding radical, which then furnishes higher aromatics through either a two-step r adical-molecule reaction or a direct radical-radical addition to another ar omatic radical. Iteration of this mechanism followed by rearrangement of th e carbon framework ultimately leads to high-molecular-mass compounds. This sequence can be repeated for the formation of high-molecular-mass compounds . The distinguishing features of the proposed model lie in the chemical spe cificity of the routes considered. The aromatic radical attacks the double bond of five-membered-ring polycyclic aromatic hydrocarbons. This involves specific compounds that are exceptional soot precursors as they form resona ntly stabilized radical intermediates, relieving part of the large strain i n the five-membered rings by formation of linear aggregates. (C) 2001 by Th e Combustion Institute.