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

这是对涉及环戊二烯 (CPD) 和含有 CPD 部分的茚的燃烧系统中多环芳烃 (PAH) 生长过程的基本分子分析。 这些存在于燃烧流出物中的化合物因其在含有五元环的潜在诱变多环芳烃的形成以及富勒烯和烟灰的形成中作为中间体的作用而受到关注。 环戊二烯和茚对于燃烧过程中 PAH 的生长非常重要，因为它们形成在多个位点具有反应性的共振稳定自由基。 研究精心设计的分子系统中涉及这些化合物的反应，可以更好地了解燃烧过程中多环芳烃生长的基本化学原理，以及控制有毒空气污染物和烟灰形成的条件。 先前的工作表明，环戊二烯基和茚基自由基会添加到包含外部 CPD 部分的母体分子（CPD 和茚）的 pi 键上。随后的反应通过以下两种途径之一导致邻位稠合 PAH 的形成：一种涉及两个五元环的扩展，通过类似于环戊二烯基自由基结合形成萘的途径，形成仅具有六元环的 PAH； 另一种涉及形成降冰片烯基型桥连中间体，然后开环并失去 C1 物质，形成保留一个 CPD 部分的 PAH。 第二条途径是以前未提出的 PAH 形成途径。 佐治亚理工学院的实验将 CPD 和茚化学工作扩展到这些化合物与其他三种物质（苯乙烯、苊和菲）的热反应。 研究了 PAH 的形成以及环戊二烯基和茚基自由基加成到其他类型的π键上的生长。 苯乙烯是最简单的芳香族分子，含有乙烯基取代基；由于乙炔含量丰富，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多环芳烃的代表；燃烧系统中发现的其他例子包括苊菲和苊。 菲是一种多环芳烃，其π键的共轭性低于其他芳香族π键；另一种具有这种特性的燃烧产生的多环芳烃是芘。因此，拟议的研究将显着扩展对燃烧系统中碳部分通过添加环戊二烯基和茚基自由基以及随后的多环芳烃融合而增长的理解。 对 CPD/茚系统进行了半经验分子建模，以研究替代的 PAH 形成途径。 PAH 产物通道之间的实验观察和计算分配之间获得了定性一致性。 量子力学理论已应用于涉及苊的碳生长过程的研究。这项研究包括在犹他州对 CPD/茚系统进行从头开始建模，以完善计算方法并验证半经验建模结果。 对正在实验研究的新环戊二烯基和茚基加成途径进行了计算研究。更广泛的影响这项研究将通过实验和计算方法的紧密配合，改善燃烧系统中多环芳烃和烟灰形成的化学机制。 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.