Reaction Dynamics of Polyatomic Molecules: Low Temperature Reactions and Coherent Photodissociation

在这个由化学系化学结构、动力学和机理A(CSDM-A)计划资助的项目中，哥伦比亚密苏里大学的Arthur Suits教授和他的研究团队正在开发新的工具来研究化学反应是如何发生的，换句话说，分子中的原子如何移动，键如何断裂和形成新的键。Suits实验室正在开发反应室，在那里，初始材料以均匀的超音速气流的形式注入。在施加激光脉冲后，在不同的下游距离观察激光引起的分子结构的变化。因为流率是精确已知的，所以下游距离对应于自激光脉冲以来的时间，并且可以计算出分子改变结构的速率。利用超音速流动可以研究非常快速的化学反应。下游事件是使用其他激光或微波光谱技术捕获的。微波光会导致一些分子以非常特殊的方式旋转，进而揭示其结构信息。正在研究的反应包括氧原子与具有双碳碳键(C=C)和三键(C≡C)的碳氢化合物反应，以及光诱导乙二硫化物(C2H4S)和二氧化氮(NO2)的解离。这些研究为化学反应是如何发生的提供了新的见解。正在研究的具体反应对于更准确地模拟大气和天文环境中的化学反应也很重要。该项目正在为一名研究生和一名博士后提供培训。研究期间开发的数据分析软件可供世界各地的其他研究小组使用。该研究利用两种独特的新仪器来探索多原子分子的反应动力学、光谱和低温动力学。其中第一台仪器将革命性的啁啾脉冲傅里叶变换微波(CPTMW)技术与强烈的低温脉冲均匀超音速流动相结合，用于动力学和动力学研究。这项研究还涉及一种仪器，它将相同的均匀超音速流动与高分辨率超灵敏连续波腔衰荡光谱(CRDS)相结合，提供与基于微波的系统的功能互补的功能。后一种仪器最近首次在超音速膨胀中演示了同步动力学和振铃(SKAR)。除了对低温流动的研究外，Suits团队还在研究相干轨道极化如何揭示所谓几何相的影响，即系统波函数在绕过圆锥形交叉口(CI)后必须经历符号变化。目前的研究将几何相的研究扩展到NO2和乙烯硫化物，有望成为对非绝热动力学的新探索和见解。在更广泛的科学影响方面，该项目将能力扩展到中红外光谱，这反过来又允许将SKAR动力学方法应用于许多天体化学和天文兴趣系统。这一奖项反映了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。

In this project funded by the Chemical Structure, Dynamics, and Mechanism-A (CSDM-A) program of the Chemistry Division, Professor Arthur Suits and his research team at the University of Missouri, Columbia are developing new tools for studying how chemical reactions occur, in other words, how the atoms within the molecules move, how bonds are broken and new ones formed. The Suits laboratory is developing reaction chambers where the starting materials are injected as uniform supersonic flows of gas. After a pulse of laser light is applied, the changes in molecular structure caused by the laser are observed at different downstream distances. Since the flow rate is known precisely, the downstream distances correspond to time since the laser pulse, and the rates at which the molecules change structure can be calculated. The use of supersonic flows allows very fast chemical reactions to be studied. The downstream events are captured using other laser or microwave spectroscopy techniques. Microwave light causes some molecules to rotate in very specific ways, which in turn reveals information about their structure. The reactions being studied include oxygen atoms reacting with hydrocarbons with double carbon-carbon bonds (C=C) and triple bonds (C≡C), and the light-induced dissociation of ethylene sulfide (C2H4S) and nitrogen dioxide (NO2). These studies are providing new insights into how chemical reactions occur in general. The specific reactions being studied are also important for more accurate modeling of chemical reactions in the atmosphere and in astronomical environments. This project is providing training for a graduate student and a post-doctoral fellow. Data analysis software developed during the research is made available to other research groups worldwide.The research takes advantage of two unique new instruments to probe the reaction dynamics, spectroscopy, and low temperature kinetics of polyatomic molecules. The first of these instruments combines the revolutionary Chirped-pulse Fourier-transform microwave (CPTMW) technique with intense low-temperature pulsed uniform supersonic flows for kinetics and dynamics studies. The research also involves an instrument that combines the same uniform supersonic flows with high-resolution ultra-sensitive continuous-wave cavity ring-down spectroscopy (CRDS), providing capabilities complementary to those of the microwave-based system. The latter instrument has recently demonstrated Simultaneous Kinetics and Ringdown (SKaR) in a supersonic expansion for the first time. In addition to the studies in low temperature flows, the Suits team is also investigating how coherent orbital polarization reveals effects of the so-called geometric phae, wherein the system wavefunction must undergo a sign change following a transit around a conical intersection (CI). The current studies extend investigations of the geometric phase to NO2 and ethylene sulfide, promising novel probes and insights into nonadiabatic dynamics. In terms of scientific Broader Impacts, this project extends capabilities into the mid-IR spectrum, which in turn permits the application of the SKaR kinetics method to many systems of astrochemical and astronomical interest.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.