Probing Low Frequency Vibrational Modes in Molecular Crystals and Developing Terahertz Spectroscopic Polarimetry

在化学系化学结构、动力学和机理（CSDM-A）项目的资助下，耶鲁大学的 Charles Schmuttenmaer 教授和他的博士后、研究生和本科生同事正在研究一种称为太赫兹振动圆二色性的技术。中红外区域的振动圆二色性（VCD）是一种非常有用的技术，可以提供分子的三维结构信息。它适用于小型和复杂系统。肌肉蛋白、DNA、氨基酸和蛋白质等物种已被研究。该项目正在将 VCD 扩展到太赫兹频谱区域（微波和红外辐射之间的中间地带）。这是一个新的领域，可以探索整个分子上发生的运动。其应用范围涵盖氨基酸晶体和碳水化合物、药品、炸药等。面向社会经济弱势的中学生和高中生有很强的外展活动。此外，耶鲁大学的本科生研究机会也将得到加强。最近有大量工作利用太赫兹时域光谱来表征有机分子晶体（OMC）的低频振动模式。虽然许多 OMC 的太赫兹光谱已被报道，但分配它们却非常困难。该项目正在使用新方法来理解这些低频模式背后的复杂运动。通过同位素替代以及对压力和温度等外部参数的依赖获得洞察力。计算和测量几种化学相关的 OMC 的光谱，以便识别和描述它们的共同运动和独特运动。测量太赫兹 VCD 光谱并提供限制可能的峰值分配的实验数据。其中一个目标是首次测量 OMC 的太赫兹 VCD 频谱。

With this award, funded by the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry, Professor Charles Schmuttenmaer of Yale University and his postdoctoral, graduate and undergraduate student colleagues are studying a technique called terahertz vibrational circular dichroism. Vibrational circular dichroism (VCD) in the mid-infra-red region is a very useful technique that provides three-dimensional structural information about molecules. It has applications for both small and complex systems. Species such as muscle proteins, DNA, amino acids, and proteins have been studied. This project is extending VCD in the terahertz region of the spectrum (the middle ground between microwave and infra-red radiation). This is a new frontier that allows the exploration of motions that occur over an entire molecule. Applications are envisaged from amino acid crystals and carbohydrates, to pharmaceuticals, to explosives, and others. There is a strong outreach component to socioeconomically disadvantaged middle- and high-school students. In addition, undergraduate research opportunities at Yale will be strengthened.There has been a great deal of recent work using THz time-domain spectroscopy to characterize the low frequency vibrational modes in organic molecular crystals (OMCs). While THz spectra of many OMCs have been reported, assigning them has been exceedingly difficult. This project is using new approaches to understand the complex motions underlying these low frequency modes. Insight is gained through isotopic substitution as well as dependence on external parameters such as pressure and temperature. The spectra of several chemically related OMCs are calculated and measured in order to identify and describe which motions are common to them, and which are unique. The THz VCD spectra are measured and provide experimental data that constrain possible peak assignments. One objective is to measure the THz VCD spectrum of an OMC for the first time.