Hyperspectral Extinction and Emission Spectroscopy of Nascent Soot: Insight into Electronic Structure and Morphology

美国每年消耗的能量中约有80%是通过燃烧过程产生的，而煤烟（或黑碳）是不完全燃烧的副产品。众所周知，煤烟对地球气候和人类健康有有害影响，气候科学家发现，黑碳是第二大人为气候强迫因子，介于二氧化碳和甲烷之间。以煤烟为主要成分的小颗粒物被认为是造成一系列心血管和呼吸问题的原因，并可能成为有毒燃烧副产品的载体，带来进一步的健康影响。因此，减少燃烧过程中的烟尘排放是一个至关重要的目标，并且有必要对燃烧系统中导致烟尘的化学和物理过程进行基本了解。在这个项目中，研究人员正在进行基于激光的光学诊断研究，旨在了解烟尘形成过程中的关键阶段。这些实验得到了计算化学计算的补充和通知。该项目的成果将包括与燃烧研究界有关的数据，以及探索黑碳前体在星际空间中的作用及其在地球上电子和太阳能转换中的潜在用途的其他科学家。最后，该项目有助于培养和准备研究生在STEM领域的职业生涯。该研究项目是基于这样的假设，即烟尘的开始是由多环芳烃（PAH）物质的聚集开始的，这些物质大到足以在火焰温度下“粘”起来。该项目包括几个新的实验，旨在解决这个想法以及竞争模型的颗粒开始，他们是：（1）宽带，腔增强吸收/消光测量在近红外光谱区的分子和颗粒物种。(2)通过紫外和可见光的二维激发/发射研究，深入了解芳香族电子结构。(3)波长灵活，角度分辨散射测量，以确定颗粒分形形态。(4)扩展计算化学，以评估电子结构在PAH及其聚集体的热力学稳定性，带隙和光谱特性中的作用。(5)一套固态诊断法在热迁移取样微粒中的应用，包括红外和拉曼光谱法以及光学和电子显微镜法。

Approximately 80% of the energy consumed in the United States annually is produced through combustion processes, and soot (or black carbon) is a by-product of incomplete combustion. Soot is known to have harmful impacts on the earth's climate and human health, and climate scientists have found that black carbon is the second most important man-made climate-forcing agent, falling between carbon dioxide and methane. Small-sized particles, of which soot is a dominant contributor, are thought to be responsible for a range of cardiovascular and respiratory problems and may act as a carrier for toxic combustion by-products, introducing further health effects. Thus, reducing emissions of soot from combustion processes is a critically important goal, and developing a fundamental understanding of the chemical and physical processes in combustion systems that lead to soot will be necessary. In this project, researchers are performing laser-based optical diagnostic studies aimed at understanding a critical phase in the soot formation process. These experiments are being complemented and informed by computational chemistry calculations. The results of the project will include data that will be of relevance to the combustion research community, as well as other scientists exploring the role of black carbon precursors in interstellar space and their potential use here on Earth in electronics and solar energy conversion. Finally, this project is helping to train and prepare graduate students for careers in STEM fields. This research project is based upon the hypothesis that soot inception begins with the agglomeration of polycyclic aromatic hydrocarbon (PAH) species that are large enough to "stick" at flame temperatures. This project involves several new experiments designed to address this idea as well as competing models for particulate inception, and they are: (1) Broadband, cavity-enhanced absorption/extinction measurements in the near infrared spectral region for both molecular and particulate species. (2) Two-dimensional excitation/emission studies through the ultraviolet and visible to gain insight in aromatic electronic structure. (3) Wavelength-agile, angle-resolved scattering measurements to define particle fractal morphology. (4) Extension of the computational chemistry to evaluate electronic structure's role in thermodynamic stability, band gaps, and spectroscopic properties of PAH and their aggregates. (5) Application of a suite of solid-state diagnostics to thermophoretically sampled particulate including infrared and Raman spectroscopies and optical and electron microscopies.