Collaborative Research: Polycyclic Aromatic Hydrocarbon Growth Mechanisms in Combustion involving Cyclopentadiene and Indene

这是多环芳烃(PAH)在环戊二烯(CPD)和含有环戊二烯(CPD)部分的吲哚燃烧体系中生长过程的基本分子分析。这些化合物存在于燃烧废气中，因为它们作为中间体参与了含有五元环的潜在致突变多环芳烃的形成，以及富勒烯和烟尘的形成。环戊二烯和吲哚对燃烧过程中多环芳烃的增长很重要，因为它们形成了共振稳定的自由基，在多个位置上都是反应的。在精心设计的分子系统中研究涉及这些化合物的反应，有助于更好地理解燃烧产生多环芳烃的潜在化学成分，以及控制有毒空气污染物和烟尘形成的条件。以前的工作表明，环戊二烯和吲基自由基增加了含有外部CPD部分的母体分子(CPD和吲哚)的pi键。随后的反应通过两条途径之一形成邻位稠合的多环芳烃：一条途径是两个五元环扩张，形成只有六元环的多环芳烃，路线类似于环戊二烯自由基结合生成萘；另一条途径是形成降冰片烯基桥联中间体，然后开环和失去一个C1物种形成保留一个CPD部分的多环芳烃。这第二条途径是以前没有提出的多环芳烃的形成途径。佐治亚理工学院的实验将CPD和吲哚化学的工作扩展到这些化合物与另外三种化合物的热反应：苯乙烯、庚和菲。研究了环戊二烯和吲基自由基加到其他类型的pi键上的PAH的形成和生长。苯乙烯是最简单的含有乙烯基取代基的芳香族分子；由于乙炔的丰富，这些物种在燃烧系统中很常见。萘是含有外部五元环的全共轭多环芳烃的代表；在燃烧系统中发现的其他例子包括乙基菲和乙基菲。菲是一种多环芳烃，它含有一个比其他芳香族pi？键更少共轭的pi？键；另一种具有这一特征的燃烧生成的多环芳烃是芘。因此，这项拟议的研究将极大地扩展对燃烧系统中碳部分增长的理解，这些增长来自环戊二烯和吲基自由基的添加以及随后的多环芳烃融合。用半经验分子模拟方法研究了多环芳烃的不同生成途径。实验观察到的多环芳烃产物通道之间的分配与计算得到了定性的一致。量子力学理论已被应用于含萘的碳生长过程的研究。这项研究包括在犹他州对CPD/indene体系进行从头计算建模，以改进计算方法并验证半经验建模结果。对实验中正在研究的环戊二烯和吲基加成反应的新途径进行了计算研究。溴化物影响本研究将通过实验和计算方法的紧密协调，改善燃烧系统中多环芳烃和碳烟形成的化学机理。该项目结合了两个机构研究人员的实验和计算专业知识。这种合作需要密切的互动，并将扩大每个小组的研究能力。

This is a fundamental molecular analysis of polycyclic aromatic hydrocarbon (PAH) growth processes in combustion systems involving cyclopentadiene (CPD) and indene, which contains the CPD moiety. These compounds, which are present in combustion effluents, are of interest because of their roles as intermediates in the formation of potentially mutagenic PAH which contain five-membered rings, as well as in the formation of fullerenes and soot. Cyclopentadiene and indene are important in growth of PAH from combustion processes because they form resonance-stabilized radicals that are reactive at multiple sites. Study of reactions involving these compounds in well-designed molecular systems leads to better understanding of the underlying chemistry of PAH growth from combustion and of conditions that control the formation of toxic air pollutants and soot. Previous work indicates that cyclopentadienyl and indenyl radicals add to the pi bonds of the parent molecules (CPD and indene) that contain external CPD moieties. Subsequent reactions lead to the formation of ortho-fused PAH via one of two pathways: one involving expansion of both five-membered rings to form PAH with only six-membered rings by a route similar to that for cyclopentadienyl radical combination to form naphthalene; the other involving formation of a norbornenyl-type bridged intermediate followed by ring opening and loss of a C1 species to form PAH that retain one CPD moiety. This second pathway is a route of PAH formation not previously proposed. Experiments at Georgia Tech extend work on CPD and indene chemistry to thermal reactions of these compounds with three other species: styrene, acenaphthylene, and phenanthrene. Formation of PAH and growth by addition of cyclopentadienyl and indenyl radicals to other types of pi?bonds is studied. Styrene is the simplest aromatic molecule that contains a vinyl substituent; these species are common in combustion systems due to the abundance of acetylene. Acenaphthylene is representative of fully conjugated PAH containing external five-membered rings; other examples found in combustion systems include acephenanthrylene and aceanthrylene. Phenanthrene is a PAH that contains a pi?bond that is less conjugated than other aromatic pi?bonds; another combustion-generated PAH with this feature is pyrene. Thus, the proposed study will significantly expand the understanding of the growth of carbon moieties in combustion systems from addition of cyclopentadienyl and indenyl radicals and subsequent PAH fusion. Semi-empirical molecular modeling has been performed on the CPD/indene system to study alternative PAH formation pathways. Qualitative agreement was obtained between experimentally observed and computed partitioning between PAH product channels. Quantum mechanical theory has been applied to the study of carbon growth processes involving acenaphthylene. This study includes ab initio modeling at Utah of the CPD/indene system to refine computational methods and verify semi-empirical modeling results. A computational study of the new cyclopentadienyl and indenyl addition pathways being investigated experimentally is conducted.Broader impactThis research will improve chemical mechanisms of PAH and soot formation in combustion systems, using a tight coordination of experimental and computational approaches. The project combines experimental and computational expertise of investigators at two institutions. This collaboration will require a close interaction and will broaden the research capabilities of each group.