New Tools and New Approaches for Spectroscopy, Kinetics and Dynamics in Uniform Supersonic Flows

哥伦比亚密苏里州大学的亚瑟·苏茨教授在化学系化学结构动力学和机理（CSDM-A）项目资助下，正在开发新的激光和微波光谱技术，以研究一系列活性分子的详细相互作用和性质（例如，含有多个键的有机分子，如丁二烯、丙二烯和丙炔）和分子簇（例如，水）。这些新方法提供了对这些分子结构的深入了解，以及这些分子在吸收能量时如何反应形成不同的产物分子。除了对该项目中考虑的分子的结构和反应性的新见解外，该研究还在继续开发激光和光谱技术，其他研究小组可以从中受益。 特别是，Suits集团正在继续开发和改进数据分析软件包（有限切片分析，或“FinA”）。 该组织免费向其他研究人员提供该软件。 除了接受尖端激光和光谱技术的培训外，参与该项目的学生还获得了从头算电子结构计算的经验，因此他们对这些方法有坚实的基础和一些实践经验。这些研究利用了两种正在开发的新仪器来探测多原子分子的反应动力学、光谱学和低温动力学。特别注意的是针对自由基物种在大气化学和天体化学的重要性。这些仪器中的第一个将啁啾脉冲傅里叶变换微波技术与强烈的低温脉冲均匀超音速流相结合，使宽带旋转光谱学在光解，产物分支，光谱学和低温动力学的研究中被用作几乎通用的工具。第二种仪器将相同的均匀超音速流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互补的能力。这两种仪器都是同类仪器中的第一种。这些研究应用于：1）探测光解反应中详细的产物支化; 2）发展微波-红外双共振方法，应用于自由基和反应中间体的振动光谱; 3）探测低温下具有新细节的反应动力学，包括振动依赖性和异构体和构象特异性，以及低丰度的瞬态自由基物种; 4）表征水团簇的热化学，例如水六聚体和其他非共价键合系统;以及5）适应敏感的CRDS方法，以检测和表征重要的大气和天体化学自由基和反应中间体，它们在流动中的低温下被动力学地捕获在局部能量最小值中。

In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Arthur Suits of the University of Missouri, Columbia, is developing new laser and microwave spectroscopy techniques to study the detailed interactions and properties a range of reactive molecules (for example, organic molecules that contain multiple bonds, like butadiene, allene and propyne) and molecular clusters (for example water). These new methods provide insight into the structures of these molecules, and how these molecules react to form different product molecules when they absorb energy. In addition to new insights about the structure and reactivity of the molecules considered in this project, the research is also continuing the development of laser and spectroscopy techniques from which other research groups can benefit. In particular, the Suits group is continuing to develop and improve a data analysis software package (Finite Slice Analysis, or "FinA"). The group makes the software available to other researchers free of charge. In addition to the training received in cutting-edge laser and spectroscopic techniques, the students involved in this project also gain experience in ab initio electronic structure calculations so they have a solid foundation and some practical experience with these methods. These studies take advantage of two new instruments being developed to probe the reaction dynamics, spectroscopy, and low temperature kinetics of polyatomic molecules. Particular attention is directed to radical species important in atmospheric chemistry and astrochemistry. The first of these instruments combines Chirped-pulse Fourier-transform microwave technique with intense low-temperature pulsed uniform supersonic flows, allowing broadband rotational spectroscopy to be used as a nearly universal tool in the study of photodissociation, product branching, spectroscopy and low temperature kinetics. The second instrument 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. Both of these instruments are the first of their kind. These studies are applied 1) to probe detailed product branching in photodissociation reactions; 2) to develop microwave-infrared double resonance methods for application to vibrational spectroscopy of radicals and reaction intermediates; 3) to probe reaction kinetics at low temperature with new detail including vibrational dependence and isomer- and conformer-specificity, and for transient radical species in low abundance; 4) to characterize the thermochemistry of water clusters such as the water hexamer and other non-covalently bound systems; and 5) to adapt sensitive CRDS methods to detect and characterize important atmospheric and astrochemical radicals and reaction intermediates kinetically trapped in local energy minima at low temperature in the flow.