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)计划的资助下，耶鲁大学的Charles Schmutenmaer教授和他的博士后、研究生和本科生同事正在研究一种名为太赫兹振动圆二色谱的技术。中红外区的振动圆二色谱(VCD)是一种非常有用的技术，它提供了关于分子的三维结构信息。它既适用于小型系统，也适用于复杂系统。对肌肉蛋白质、DNA、氨基酸和蛋白质等物种进行了研究。该项目正在将VCD扩展到频谱的太赫兹区域(微波和红外辐射之间的中间地带)。这是一个新的前沿，它允许探索在整个分子上发生的运动。从氨基酸晶体和碳水化合物，到制药，到炸药等，都有应用前景。对社会经济上处于不利地位的初中生和高中生有很强的外展作用。此外，耶鲁大学的本科生研究机会将得到加强。最近有大量工作使用太赫兹时间域谱来表征有机分子晶体(OMC)中的低频振动模式。虽然已经报道了许多OMC的太赫兹光谱，但分配它们一直是极其困难的。这个项目正在使用新的方法来理解这些低频模式背后的复杂运动。洞察力是通过同位素替代以及对压力和温度等外部参数的依赖来获得的。计算和测量了几个化学上相关的OMC的光谱，以便识别和描述哪些运动是它们共同的，哪些是独特的。测量了太赫兹VCD光谱，并提供了限制可能的峰分配的实验数据。其中一个目标是首次测量OMC的太赫兹VCD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.