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Two Dimensional TeraHertz Spectroscopy of Molecular Liquids

分子液体的二维太赫兹光谱

基本信息

批准号：
1665467
负责人：
Geoffrey Blake
金额：
$ 68万
依托单位：
California Institute of Technology
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-08-15 至 2022-09-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1665467&HistoricalAwards=false
关键词：
Two Dimensional TeraHertz Spectroscopy Molecular

项目摘要

In this project funded by the Chemical Structure Dynamics and Mechanism A (CSDM-A) and Chemical Measurement and Imaging (CMI) Programs of the Chemistry Division, Professors Geoffrey Blake and Tom Miller of the California Institute of Technology are using new laser techniques to study the properties of pure molecular liquids and mixtures, especially those containing hydrogen bonds (for example water and alcohols). Specifically, the new laser tools involve light at terahertz (THz) frequencies (this frequency range lies between the infrared and microwave parts of the light spectrum). These THz lasers are also designed to produce extremely short pulses of light (a few femtoseconds, where a femtosecond is one quadrillionth of one second). The femtosecond THz laser pulses are then used to probe the motions of the liquid molecules as they interact with other reactive molecules dissolved in the liquid. The THz pulses also make it possible to control the orientation of the molecules in the liquid, and to examine how energy flows between two reacting molecules or between the molecules and the liquid. Professors Blake and Miller combine the experimental data with computer simulations of liquids and clusters of molecules to build better models for understanding chemical reactions in liquids. The broader impacts of this work include potential societal benefits from an increased understanding of how liquids solvate molecules and influence chemical reactivity, as well as opportunities for the training of graduate students and undergraduates in the design and construction of advanced experimental instrumentation and complex computer simulation. The Blake and Miller research groups also engage the local K-12 community, for example via the Caltech Pre-College Science Initiative (CAPSI) program (Prof. Blake) and Prof. Miller's Team Research yielding Integrated Educational Tools (TRIDENT) program.The project focuses on the nonlinear THz spectroscopy of neat liquids and mixtures at various temperatures. Detailed molecular pictures of the structure and dynamics of liquids drive our understanding of chemistry and biology. Nonlinear two dimensional (2D)-infrared and nuclear magnetic resonance (NMR) spectroscopies have revealed many specifics of liquid behavior. Extending such tools into the THz regime would directly probe liquid dynamics supported by intermolecular forces. This research project does so by combining two intense THz pulses whose arrival at the sample can be swept over controlled delays, with the subsequent anisotropy and Raman spectrum of the liquid probed by a third pulse at 800 nm. By mapping out the liquid response over the relative delays between the three pulses, a 2D-THz-THz-Raman (2D-TTR) spectrum is obtained. This method inherently suppresses the linear response of the system, and so is sensitive to anharmonicities in the intermolecular liquid potential energy surface and the electric dipole moment and Raman polarizability surfaces. To determine the origins of the observed response, the experimental observations are interpreted with theoretical calculations both of molecular clusters and liquid models. The cluster work involves high accuracy electronic structure calculations, while the liquid simulations are based on molecular dynamics approaches.

在这项由化学部化学结构动力学与机理A(CSDM-A)和化学测量与成像(CMI)计划资助的项目中，加州理工学院的Geoffrey Blake教授和Tom Miller教授正在使用新的激光技术来研究纯分子液体和混合物的性质，特别是那些含有氢键的液体和混合物(例如水和醇)。具体地说，新的激光工具涉及太赫兹(THz)频率的光(该频率范围位于光谱的红外和微波部分之间)。这些太赫兹激光还被设计成产生极短的光脉冲(几飞秒，其中一飞秒是一万亿分之一秒)。然后，飞秒太赫兹激光脉冲被用来探测液体分子与溶解在液体中的其他活性分子相互作用时的运动。太赫兹脉冲还可以控制分子在液体中的取向，并检查能量如何在两个反应分子之间或分子和液体之间流动。布莱克和米勒教授将实验数据与液体和分子簇的计算机模拟相结合，建立了更好的模型来理解液体中的化学反应。这项工作的更广泛的影响包括增加对液体如何使分子溶解并影响化学反应的了解的潜在社会益处，以及为研究生和本科生提供设计和建造先进的实验仪器和复杂的计算机模拟的机会。布莱克和米勒的研究小组还与当地的K-12社区接触，例如通过加州理工大学预科科学倡议(CAPSI)计划(布莱克教授)和米勒教授的团队研究产生综合教育工具(三叉戟)计划。该项目专注于不同温度下纯净液体和混合物的非线性太赫兹光谱。液体结构和动力学的详细分子图片推动了我们对化学和生物学的理解。非线性二维红外和核磁共振光谱揭示了液体行为的许多细节。将这些工具扩展到太赫兹区域将直接探测分子间力支持的液体动力学。这项研究项目将两个到达样品的强太赫兹脉冲组合在一起，可以在受控的延迟内扫描，随后在800 nm处用第三个脉冲探测液体的各向异性和拉曼光谱。通过绘制三个脉冲之间的相对延迟上的液体响应图，得到了2D-THz-THz-Ramon(2D-TTR)谱。这种方法固有地抑制了体系的线性响应，因此对分子间液体势能面、电偶极矩和拉曼极化面的非谐性很敏感。为了确定观测到的响应的来源，用分子团簇和液体模型的理论计算来解释实验观测结果。团簇工作涉及高精度的电子结构计算，而液体模拟则基于分子动力学方法。