New Tools and Applications for Kinetics and Dynamics with Broadband Rotational Spectroscopy

在化学系化学结构、动力学和机理(CSDM-A)项目的支持下，密苏里-哥伦比亚大学的Arthur Suits教授正在开发新的工具，允许应用啁啾脉冲傅里叶变换微/毫米波光谱来研究自由基反应的低温动力学。首先要研究的反应包括甲酰和乙酰基与稳定的开壳分子NO和O2的反应，以及涉及氢原子和氨基的反应。将作为这些研究的主题的自由基-自由基反应在广泛的极端环境中是重要的。然而，它们在实验上的研究是非常具有挑战性的，而且不容易用“黄金标准”的理论方法来处理。这些研究可以更好地理解复杂体系中的化学反应，对电子结构理论家积极研究的固有多参照系的理论特征进行基准测试，并对天体化学、大气化学和燃烧产生影响。学生和博士后将接受最先进的仪器开发方法、反应动力学和光化学、动力学和动力学建模、数据分析以及天体化学和大气化学问题的培训。开发的技术将免费与更广泛的社区共享。宽带旋转光谱是一种强大的、近乎通用的探针技术，但将其耦合到低温流动环境中进行动力学测量存在挑战。将流量采样到单独的检测区域是可能的，但这可能会引入冲击并产生干扰测量的非平衡条件。相反，Suits教授和他的学生将开发一种在其中发生反应的加长喷嘴，然后是无冲击的二次膨胀到低压，这是旋转光谱分析的理想选择。Suits教授和他的学生还将把共振增强多光子电离(REMPI)耦合到低温流动环境中，以探索这些具有挑战性的自由基-自由基反应的低温动力学、产品分支和动力学。这一策略将被用来检测氢原子和其他原子物种，用于动力学测量，否则在流动环境中很难或不可能探测到这些原子。他们还将采用REMPI技术来确定加长喷嘴内的条件，这对于验证用于确定速率的条件至关重要。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program in the Division of Chemistry, Professor Arthur Suits of the University of Missouri-Columbia is developing new tools to permit applications of Chirped-Pulse Fourier-Transform Micro/Millimeter Wave Spectroscopy to study low temperature kinetics of radical-radical reactions. The first reactions to be studied include formyl and acetyl radicals with the stable open shell molecules NO and O2 as well as reactions involving hydrogen atoms and amino radicals. The radical-radical reactions that will be the subject of these studies are important in a wide range of extreme environments. However, they are very challenging to investigate experimentally, and are not readily treated by the “gold standard” theoretical approaches. These studies could lead to a better understanding of chemical reactivity in complex systems, benchmark the theoretical characterization of inherently multireference systems that are the subject of active investigation by electronic structure theorists, and have implications for astrochemistry, atmospheric chemistry, and combustion. Students and post-docs will be trained in state-of-the-art instrument development methods, in reaction dynamics and photochemistry, in kinetics and kinetic modeling, in data analysis, and issues in astrochemistry and atmospheric chemistry. Techniques developed will be freely shared with the broader community.Broadband rotational spectroscopy is a powerful, near-universal probe technique but there are challenges in coupling it to the low temperature flow environment for kinetics measurements. Sampling the flow to a separate detection region is possible but this can introduce shocks and produce nonequilibrium conditions that interfere with the measurements. Professor Suits and his students will instead develop an extended nozzle in which the reactions take place, which is then followed by a shock-free second expansion to low pressure ideal for detection by rotational spectroscopy. Professor Suits and his students will also couple Resonance Enhanced Multiphoton Ionization (REMPI) to the low temperature flow environment to probe low temperature kinetics, product branching, and dynamics for these challenging radical-radical reactions. This strategy will be used to detect hydrogen atoms and other atomic species for kinetics measurements which are otherwise difficult or impossible to probe in the flow environment. They will also adapt the REMPI technique to determine the conditions inside the extended nozzle which will be essential to validate the conditions used for the rate determinations.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.