CAREER: Tiny Drops of Acid: Microwave Spectroscopy and Isomer-resolved IR Spectroscopy of Hydrohalic Acid-Water Clusters

在化学系化学结构、动力学和机理A （CSDM-A）项目的支持下，德克萨斯理工大学的G. Barratt Park正在开发基于宽带微波光谱的工具，用于复杂混合物中簇的自动分配和结构确定。微波结构将与同分异构体分辨红外测量相结合，以获得关于小的氢盐酸-水团簇的详细信息。微波光谱学是一种测定分子或分子簇精确三维结构的有力方法，但从未知分子种类的混合物中获得的光谱由于其纯粹的复杂性而极具挑战性。Park博士和他的学生将使用自动化微波和红外光谱技术来解开复杂的模式，并了解世界上最小的酸滴的结构和振动动力学，酸滴由单个酸分子和少量水分子溶解组成。他们的研究可以为水性团簇的理论描述提供关键的基准，并可能导致从混合物的微波光谱确定化学结构的重大进展。朴小组将开发微波光谱仪，为大学生提供动手指导，并将与未来科学家的中学女生一起开展社区服务。频率柔性宽带微波光谱技术的进步为复杂混合物中的微波结构测定提供了全新的方法。目前自动分配算法的能力将扩展到更复杂的非刚性哈密顿量。本研究的主要目标将是具有单个HX分子和3-10个水分子的氢卤酸-水簇。到目前为止，现有的光谱方法只能对少于三个水分子的非常小的簇进行微波结构和明确的、无可争议的红外分配。这项研究的一个关键目标将是获得导致解离的最小簇的结构和振动动力学的高分辨率测量。簇的同位素取代将以一种可控的方式变化，促进了一套完整的取代结构的分配，这将允许确定微波结构。用红外-微波双共振获得中性团簇的同分异构体分辨红外光谱。所提议的工作将使方法学上的进步能够朝着一个难以实现的目标取得进展，即允许非专家以一种有效的方式从混合物的微波光谱中确定化学结构。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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, G. Barratt Park of Texas Tech University is developing broadband microwave spectroscopy-based tools for the automated assignment and structure determination of clusters in complex mixtures. The microwave structures will be combined with isomer-resolved IR measurements to obtain detailed information about small hydrohalic acid-water clusters. Microwave spectroscopy is a powerful method for determining the precise three-dimensional structure of a molecule or cluster of molecules, but spectra obtained from mixtures of unknown molecular species are extremely challenging to interpret because of their sheer complexity. Dr. Park and his students will use automated microwave and infrared spectroscopy techniques to unravel the complicated patterns and learn about the structure and vibrational dynamics of the world’s tiniest drops of acid, consisting of a single acid molecule dissolved by a handful of water molecules. Their studies could provide crucial benchmarks for the theoretical description of aqueous clusters and could lead to significant advances in chemical structure determination from microwave spectra of mixtures. The Park group will develop a microwave spectrometer to provide hands-on instruction for undergraduate students and will perform community outreach with future-scientist middle school girls. Technological advances in frequency-flexible broadband microwave spectroscopy enable entirely new approaches to microwave structure determination in complex mixtures. The current capabilities of automated assignment algorithms will be extended to more complex, non-rigid Hamiltonians. The primary target of this investigation will be hydrohalic acid-water clusters with a single HX molecule and 3-10 water molecules. To date, existing spectroscopic approaches have only enabled microwave structures and unambiguous, undisputed IR assignment of very small clusters with fewer than three water molecules. A key goal of this investigation will be to obtain high-resolution measurements of the structure and vibrational dynamics of the smallest clusters that lead to dissociation. The isotopic substitution of the clusters will be varied in a controlled way, facilitating the assignment of a complete set of substitution structures, which will allow the determination of the microwave structure. Isomer-resolved IR spectra of neutral clusters will be obtained by IR-microwave double resonance. Advances in methodology that will be enabled by the proposed work could make progress towards the elusive goal of allowing chemical structures to be determined from microwave spectra of mixtures in an efficient way by a non-expert.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.