• PCCP-14-4081-4096

A quantitative study of the clustering of polycyclic aromatic hydrocarbons at high temperatures

Authors: Tim Totton, Alston J. Misquitta, and Markus Kraft*

Reference: Physical Chemistry Chemical Physics 14, 4081-4096, (2012)


The clustering of polycyclic aromatic hydrocarbon (PAH) molecules is investigated in the context of soot particle inception and growth using an isotropic potential developed from the benchmark PAHAP potential. This potential is used to estimate equilibrium constants of dimerisation for five representative PAH molecules based on a statistical mechanics model. Molecular dynamics simulations are also performed to study the clustering of homomolecular systems at a range of temperatures. The results from both sets of calculations demonstrate that at flame temperatures pyrene (C16H10) dimerisation cannot be a key step in soot particle formation and that much larger molecules (e.g. circumcoronene, C54H18) are required to form small clusters at flame temperatures. The importance of using accurate descriptions of the intermolecular interactions is demonstrated by comparing results to those calculated with a popular literature potential with an order of magnitude variation in the level of clustering observed. By using an accurate intermolecular potential we are able to show that physical binding of PAH molecules based on van der Waals interactions alone can only be a viable soot inception mechanism if concentrations of large PAH molecules are significantly higher than currently thought.

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*Corresponding author:
Telephone: +44 (0)1223 762784 (Dept) 769010 (CHU)
Address: Department of Chemical Engineering and Biotechnology
University of Cambridge
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Philippa Fawcett Drive
Cambridge CB3 0AS
United Kingdom
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