Collaborative: Terahertz Spectroscopy of Clathrates

合作：包合物的太赫兹光谱

• 批准号: 2055417
• 负责人: Daniel Mittleman
• 金额: $ 40万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-15 至 2024-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2055417&HistoricalAwards=false
• 关键词: Collaborative; Terahertz; Spectroscopy; Clathrates

This project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, a collaboration between Professor Daniel Mittleman of Brown University and Professor Michael Ruggiero of the University of Vermont, focuses on the study of the vibrational motions of clathrate materials. Clathrates are porous materials consisting of small molecules, often called ‘guests’, held within a cage formed by a network of ‘host’ molecules. The host molecules can be of many different types, including the crucial example in which the host cage structure is formed by water molecules. These water clathrates can enclose various guest molecules such as methane and other greenhouse gases. Methane clathrates of this type can form naturally in the environment, and are plentiful in the permafrost and at the bottom of the ocean. They are also one of the primary sources of clogs in natural gas pipelines. It is now understood that the vibrational modes of these macromolecular structures, especially those vibrations which oscillate at relatively low frequency, are intimately related to many properties of clathrates including their formation and dissociation dynamics and their chemical reactivity. The collaborative research team is using radiation in the terahertz range of the spectrum (higher frequency than microwaves, but lower than most infrared measurements) to study how these vibrational motions are influenced by temperature, pressure, and the local chemical environment. They are understanding critical chemical reactions involving clathrates, such as the reaction in which an existing guest molecule (e.g., methane) is exchanged with a new one (e.g., carbon dioxide), thus storing the carbon dioxide while extracting the methane. In parallel to these research efforts, the project personnel are coordinating summer workshops for high school students that are offered at both Brown and the University of Vermont, expanding the reach of this research to the next generation of early career scientists. The goal of this research program is to investigate fundamental questions about the kinetics and dynamics that drive the formation and properties of clathrates using terahertz (THz) spectroscopy (0.3 – 4 THz), and to develop a new theoretical framework for interpreting these measurements which accurately accounts for the anharmonicity of the relevant modes. The thermodynamic and structural properties of clathrates are generally well characterized, but the microscopic origins of these macroscopic phenomena remain unknown. As a result, there are many open questions concerning their kinetics of formation and dissociation, vibrational dynamics, structural phase transitions, and stability. This research is employing recently developed techniques for pressure- and temperature-dependent terahertz spectroscopy to characterize the low-frequency modes of various clathrate compounds, and to observe the evolution of the vibrational landscape as reactions such as the guest exchange reaction unfold. The researchers are developing new theoretical tools for the ab initio prediction of these spectra. This approach incorporates a rigorous description of anharmonicity into the vibrational analysis, which is critical for accurately describing the relevant low-frequency modes, as well as many thermodynamic quantities. Finally, the project personnel are also developing a new interdisciplinary course for undergraduate and graduate students covering ultrafast spectroscopy in the chemical sciences, which serves both institutions, as well as the greater STEM community, by filling in this important area of modern chemical research.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.

本项目由布朗大学的Daniel Mittleman教授和佛蒙特大学的Michael Ruggiero教授合作，由化学学部化学结构动力学和机理（CSDM-A）项目资助，重点研究笼形物材料的振动运动。笼形物是由小分子组成的多孔材料，通常被称为“客人”，被关在由“宿主”分子网络形成的笼子里。宿主分子可以有许多不同的类型，包括宿主笼结构由水分子形成的关键例子。这些水包合物可以包裹各种客体分子，如甲烷和其他温室气体。这种类型的甲烷包合物可以在环境中自然形成，并且在永久冻土和海洋底部大量存在。它们也是天然气管道堵塞的主要来源之一。现在人们了解到，这些大分子结构的振动模式，特别是那些振动频率相对较低的振动模式，与笼形物的许多性质密切相关，包括它们的形成和离解动力学以及它们的化学反应性。合作研究小组正在使用太赫兹光谱范围内的辐射（频率高于微波，但低于大多数红外测量）来研究这些振动运动如何受到温度、压力和当地化学环境的影响。他们正在理解与包合物有关的关键化学反应，例如现有的客体分子（如甲烷）与新的客体分子（如二氧化碳）交换的反应，从而在提取甲烷的同时储存二氧化碳。在这些研究工作的同时，项目人员正在协调布朗大学和佛蒙特大学为高中生提供的暑期讲习班，将这项研究的范围扩大到下一代早期职业科学家。本研究计划的目标是利用太赫兹（0.3 - 4太赫兹）光谱研究驱动包合物形成和性质的动力学和动力学的基本问题，并开发一个新的理论框架来解释这些测量结果，准确地解释相关模式的非调和性。包合物的热力学和结构性质通常被很好地表征，但这些宏观现象的微观起源仍然未知。因此，在它们的形成和解离动力学、振动动力学、结构相变和稳定性方面存在许多悬而未决的问题。这项研究采用了最近开发的压力和温度相关的太赫兹光谱技术来表征各种笼形化合物的低频模式，并观察反应（如客体交换反应）展开时振动景观的演变。研究人员正在开发新的理论工具来从头开始预测这些光谱。这种方法结合了振动分析中对非谐性的严格描述，这对于准确描述相关的低频模式以及许多热力学量至关重要。最后，项目人员还为本科生和研究生开发了一门新的跨学科课程，涵盖化学科学中的超快光谱，通过填补现代化学研究的这一重要领域，为两个机构以及更大的STEM社区服务。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。