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

这是一个基本的分子分析的多环芳烃（PAH）的增长过程中的燃烧系统，涉及环戊二烯（CPD）和茚，其中包含CPD部分。 这些存在于燃烧流出物中的化合物之所以引起人们的兴趣，是因为它们在形成含有五元环的潜在致突变多环芳烃以及富勒烯和烟灰的形成中作为中间体。 环戊二烯和茚在燃烧过程中PAH的增长中很重要，因为它们形成在多个位点反应的共振稳定的自由基。 研究涉及这些化合物在精心设计的分子系统中的反应，可以更好地了解燃烧中PAH生长的基本化学过程，以及控制有毒空气污染物和烟尘形成的条件。 先前的工作表明，C12和茚基自由基添加到含有外部CPD部分的母体分子（CPD和茚）的π键。随后的反应导致邻位稠合的PAH通过两种途径之一形成：一种涉及两个五元环的膨胀，通过类似于α自由基结合形成萘的途径形成仅具有六元环的PAH;另一种涉及形成α-丁烯基型桥接中间体，然后开环和失去C1物质，形成保留一个CPD部分的PAH。 这第二个途径是以前没有提出的PAH形成途径。 格鲁吉亚理工学院的实验将CPD和茚化学的工作扩展到这些化合物与其他三种物质的热反应：苯乙烯，苊烯和菲。 PAH的形成和增长，此外，其他类型的π和茚基自由基？债券研究。 苯乙烯是含有乙烯基取代基的最简单的芳香族分子;由于乙炔的丰富，这些物质在燃烧系统中很常见。 苊烯是含有外部五元环的完全共轭PAH的代表;在燃烧系统中发现的其他例子包括醋菲烯和醋蒽烯。 菲是一种含有π的多环芳烃？比其他芳香族π键共轭较少的键？另一种燃烧产生的具有这种特征的PAH是芘。因此，拟议中的研究将显着扩大的碳部分在燃烧系统中的增长的理解，从另外的α-和茚基自由基和随后的PAH融合。 半经验分子模拟已进行CPD/茚系统，以研究替代PAH的形成途径。 实验观察到的和计算的PAH产品通道之间的分区之间获得了定性协议。 量子力学理论已被应用于研究涉及苊烯的碳生长过程。本研究包括从头建模在犹他州的CPD/茚系统，以完善计算方法和验证半经验建模结果。 计算研究的新的正己烷和茚基加成途径正在实验研究carried. broaderimpactThis研究将提高化学机理的多环芳烃和碳烟的形成在燃烧系统中，使用紧密协调的实验和计算方法。 该项目结合了两个机构研究人员的实验和计算专业知识。这种合作将需要密切的互动，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.