Isomer selective interrogation of combustion and atmospheric intermediates

在化学学部化学结构动力学与机理a （CSDM-A）项目资助下，太平洋大学Bálint Sztáray教授利用质谱法和光电子能谱法的结合，研究了与大气化学相关的不稳定和难以捉摸的分子的化学反应。质谱法是一种根据分子或原子的质量和电荷分离分子或原子的技术。光电子能谱是一种利用光（通常来自激光）从原子或分子中射出电子的技术。射出电子的能量提供了电子与分子结合的强度的信息。Sztáray教授将这两种技术结合起来，形成了光电子-光离子重合光谱或“PEPICO”，它提供了更详细的分子指纹，并能够分析许多组分的气体混合物。利用瑞士的原型仪器和位于伯克利先进光源的新桑迪亚国家实验室设备，研究了与燃烧、大气或星际环境相关的不稳定中间物质的反应。参与该项目的学生在一个尖端的实验、高度协作的环境中接受培训。由于Sztáray实验室的研究涉及定制的仪器，研究生研究人员学习独特的设计和制造技能，这在高科技领域非常有价值。研究生和本科生研究人员也有机会与美国国家实验室（桑迪亚和劳伦斯伯克利国家实验室）以及国际机构（瑞士光源）的合作者合作。在PEPICO符合检测中，每个光电子都被其对应的光离子的质荷比（m/z）“标记”，本质上结合了质谱法和光电子能谱法的优点。该项目采用侧采样、脉冲激光光解流管反应器，重点研究难以捉摸的中间体的光谱和热化学，如烷基过氧和氢过氧烷基自由基、酮氢过氧化物和Criegee中间体。利用PEPICO检测的异构体选择性，对小碳自由基与小碳氢化合物的反应进行了系统的研究。丙炔、烯丙基和苯基自由基的重组反应在最终导致烟灰形成的分子量增长过程中起着至关重要的作用。在这里，PEPICO检测为理解这些反应途径和提供同分异构体选择性分支比和反应速率提供了一步。最终，通过确定关键中间体及其反应机制和速率，可以构建更完整的燃烧模型，从而更好地预测燃烧产物，包括气体和气溶胶污染物。这些预测可以帮助开发低排放发动机技术。

In this project funded by the Chemical Structure Dynamics and Mechanism-A (CSDM-A) program of the Chemistry Division, Professor Bálint Sztáray of the University of the Pacific is using a combination of mass spectrometry and photoelectron spectroscopy to study the chemical reactions of unstable and elusive molecules that are relevant to atmospheric chemistry. Mass spectrometry is a technique that separates molecules or atoms according to their mass and electrical charge. Photoelectron spectroscopy is a technique that uses light (typically from a laser) to eject electrons from atoms or molecules. The energy of the ejected electrons gives information about how strongly the electron was bound to the molecule. Professor Sztáray combines these two techniques to form photoelectron-photo-ion coincidence spectroscopy or "PEPICO", which provides a much more detailed molecular fingerprint, and enables the analysis of gaseous mixtures of many components. With a prototype instrument in Switzerland and with a new Sandia National Lab apparatus at the Advanced Light Source in Berkeley, reactions of unstable intermediate species, relevant in combustion, atmospheric, or interstellar environments are studied. The students involved in this project are receiving training in a cutting-edge experimental, highly collaborative environment. As the research in the Sztáray laboratory involves custom-built instruments, graduate student researchers learn unique design and fabrication skills which are highly valued in the high-tech sector. Graduate and undergraduate researchers also have opportunities to work with collaborators at US National Laboratories (Sandia and Lawrence Berkeley National Laboratories) as well as international facilities (Swiss Light Source).In PEPICO coincidence detection, each photoelectron is "labeled" with the mass-to-charge ratio (m/z) of the photoion it corresponds to, essentially combining the advantages of mass spectrometry and photoelectron spectroscopy. Using a side-sampled, pulsed-laser photolysis flow-tube reactor, the project focuses on the spectroscopy and thermochemistry of elusive intermediates, such as alkylperoxy and hydroperoxyalkyl radicals, ketohydroperoxides and Criegee intermediates. Utilizing the isomer selectivity of PEPICO detection, a systematic study is conducted on the reactions of small carbon-containing radicals with small hydrocarbons. Recombination reactions of propargyl, allyl, and benzyl radicals play a crucial role in molecular weight growth processes that ultimately lead to soot formation. Here, PEPICO detection offers a step forward in understanding these reactive pathways and providing isomer selective branching ratios and reaction rates. Ultimately, by identifying key intermediates, their reaction mechanisms, and rates, more complete combustion models can be constructed, leading to better predictions of combustion products, including gaseous and aerosol pollutants. These predictions can then aid in the development of low-emission engine technologies.