RUI: Microsolvation and halogen substitution effects in weakly bound complexes and carbocations

在这个由化学部化学结构、动力学和机理A （CSDM-A）项目资助的项目中，东伊利诺伊大学的Sean Peebles教授和Rebecca Peebles教授正在使用微波辐射和计算技术研究二氧化碳（CO2）在某些条件下如何像溶剂一样，以与水溶解其他分子和离子的方式大致相同的方式发挥作用。高度压缩的二氧化碳表现为流体，比工业过程中使用的许多石油衍生溶剂更环保，更通用。然而，二氧化碳多功能性的原因还没有得到很好的理解。在皮布尔斯的实验室里，一个溶质分子与一个或几个CO2溶剂分子分离。通过微波辐射探测这些小簇，可以确定溶剂分子的排列。系统地改变二氧化碳分子的数量有助于理解其作为溶剂的独特性质。在第二个相关的研究领域，带电分子（碳正离子）的产生和它们的结构是通过与微波辐射的相互作用研究的。与二氧化碳簇一样，这提供了有关原子排列的信息，在这种情况下，有助于回答有关化学反应中原子重新排列的具体步骤的问题。本研究的两个方面也利用计算研究来提供更多关于化学结构中电子排列的信息。这一研究结果可能会推动二氧化碳作为溶剂在重要化学过程中的应用。该项目利用傅里叶变换微波光谱研究不稳定化学物质的结构。其中一个主题是在所研究的化学结构中卤素原子取代的影响。在CO2微溶剂化研究中，利用真空室中的超音速膨胀产生团簇。对具有不同氟取代量的簇的检查有助于理解为什么氟化物种在超临界CO2中具有异常高的溶解度。改变一个簇中二氧化碳分子的数量，可以观察到当溶剂化发生时，分子间的弱相互作用是如何变化的。从这些研究中获得的知识也可能有助于理解和使用定制设计的分子构建二氧化碳封存框架。在第二部分的研究中，利用脉冲放电喷嘴或电子枪与超音速膨胀一起产生碳正离子。然后用微波辐射探测提供结构信息，帮助科学家了解碳正离子是以环还是非环形式存在，以及随着卤素取代的变化，结构是如何变化的。除了对二氧化碳工业使用的影响外，更广泛的影响是对化学和其他STEM领域本科生的动手教育。学生将获得重要的实践、解决问题和计算机技能，并提高他们的批判性思维能力。

In this project, funded by the Chemical Structure, Dynamics and Mechanism A (CSDM-A) program of the Chemistry Division, Professor Sean Peebles and Professor Rebecca Peebles of Eastern Illinois University are using microwave radiation and computational techniques to study how carbon dioxide (CO2) can, under certain conditions, act like a solvent in much the same manner that water can dissolve other molecules and ions. Highly compressed CO2 behaves as a fluid, and is more environmentally friendly and more versatile than many petroleum-derived solvents used in industrial processes. However, the reasons for CO2's versatility are not well understood. In the Peebles' laboratory, a single molecule of solute is isolated with one or a few CO2 solvent molecules. By probing these small clusters with microwave radiation, the arrangement of solvent molecules can be determined. Systematically varying the number of CO2 molecules builds understanding of its unique properties as a solvent. In a second related area of research, electrically charged molecules (carbocations) are generated and their structures are studied via interactions with microwave radiation. As with the CO2 clusters, this provides information about the arrangement of atoms, in this case helping answer questions about the specific steps by which atoms rearrange during a chemical reaction. Both aspects of this research also utilize computational studies to provide more information about the arrangement of electrons within the chemical structures. The results of this research may advance the use of CO2 as a solvent in important chemical processes.The project uses Fourier-transform microwave spectroscopy for investigating structures of unstable chemical species. A theme is the effect of halogen atom substitution within the chemical structures studied. In CO2 microsolvation studies, clusters are generated using a supersonic expansion into a vacuum chamber. Examination of clusters with varying amounts of fluorine substitution builds towards an understanding of why fluorinated species have unusually high solubility in supercritical CO2. Varying the number of CO2 molecules in a cluster allows observation of how weak intermolecular interactions vary as solvation occurs. The knowledge gained from these studies may also help in understanding and building CO2 sequestration frameworks using custom designed molecules. In the second part of the research, carbocations are generated using a pulsed discharge nozzle or electron gun together with the supersonic expansion. Probing with microwave radiation then provides structural information, helping scientists to understand whether carbocations exist in cyclic or noncyclic forms, and how structures change as halogen substitution is varied. In addition to implications for industrial use of CO2, broader impacts are hands-on education of undergraduate students in Chemistry and other STEM fields. Students gain significant practical, problem solving and computer skills and improve their critical thinking abilities.