Department of Chemical Engineering and Biotechnology, University of Cambridge, New Museums Site, Pembroke Street, Cambridge, CB2 3RA, United Kingdom.
Phys Chem Chem Phys. 2012 Mar 28;14(12):4081-94. doi: 10.1039/c2cp23008a. Epub 2012 Feb 15.
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 (C(16)H(10)) dimerisation cannot be a key step in soot particle formation and that much larger molecules (e.g. circumcoronene, C(54)H(18)) 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.
采用各向同性势模拟多环芳烃（PAH）分子簇聚，该势由基准 PAHAP 势开发得到，用于研究烟尘颗粒初始形成和增长过程中 PAH 分子的二聚化平衡常数。基于统计力学模型，利用该势能估计了 5 种代表性 PAH 分子的二聚化平衡常数。还进行了分子动力学模拟，研究了同系物体系在一系列温度下的聚集情况。两组计算结果均表明，在火焰温度下，苝（C(16)H(10)）二聚化不可能是烟尘颗粒形成的关键步骤，而在火焰温度下形成小团簇则需要更大的分子（如，冠状烯，C(54)H(18)）。通过比较与文献中常用势计算结果的差异（观察到的聚集程度相差一个数量级），证明了使用准确的分子间相互作用描述的重要性。通过采用准确的分子间势能，我们可以表明，如果大 PAH 分子的浓度显著高于目前的认识，那么仅基于范德华相互作用的 PAH 分子的物理结合才可能是一种可行的烟尘初始形成机制。
