MRI: Development of a broadband terahertz electron paramagnetic resonance spectrometer

该奖项由主要研究仪器、化学研究仪器和化学测量与成像项目支持。麻省理工学院的基思·纳尔逊教授和他的同事罗伯特·格里芬开发了一种宽带太赫兹（THz）电子顺磁共振（EPR）光谱仪。太赫兹能量也被称为亚毫米辐射，太赫兹波，它的频率非常高，在电磁波谱中介于红外辐射和微波辐射之间。新仪器能够测量线性响应EPR光谱和非线性EPR光谱，包括二维（2D）光谱。它使用了一个放大飞秒（十亿分之一秒的百万分之一）激光系统和一个9.4特斯拉的低温磁铁（一种工作在低温下的磁铁）来提高灵敏度。测量使用太赫兹场进行，使用独特的基于波导的太赫兹信号产生和读出平台。一般来说，EPR光谱仪产生分子和固态材料的几何和电子结构的详细信息。它还用于获取有关自由基的寿命的信息，这些自由基是短命的、高活性的物质，参与有价值的化学转化，以及可能的病理生长的开始。这些研究影响了许多领域，从无机和有机分子的合成到新型固态材料的开发，再到磁性和生物学的化合物。从正在进行的研究中获得灵感，该仪器是麻省理工学院本科生和研究生研究和教学中不可或缺的一部分。它也被许多合作机构的研究人员使用，如加州大学伯克利分校和加州大学戴维斯分校。新的光谱仪具有任何商用仪器都没有的功能。该EPR光谱仪支持使用分子磁体的稳态太赫兹EPR光谱和过渡金属光化学（加州大学伯克利分校）的时间分辨太赫兹EPR光谱以及金属蛋白的零场和高场太赫兹EPR进行研究。它也被用于测试异金属氧化模型的析氧反应催化剂（UC Davis）和研究量子自旋液态。新的光谱仪对于评估提供1D Ising链中分数自旋激发信息的化合物至关重要，其中Ising代表了统计力学中使用的铁磁性数学模型，可以识别相变。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。

This award is supported by the Major Research Instrumentation, the Chemistry Research Instrumentation and the Chemical Measurements and Imaging programs. Professor Keith Nelson from MIT and colleague Robert Griffin have developed a broadband terahertz (THz) electron paramagnetic resonance (EPR) spectrometer. The terahertz energy is also known as submillimeter radiation, terahertz waves, which have an extremely high frequency that falls in between infrared radiation and microwave radiation in the electromagnetic spectrum. The new instrument is capable of measuring both linear-response EPR spectra and nonlinear EPR spectra including two-dimensional (2D) spectra. It uses an amplified femtosecond (one millionth of one billionth of a second) laser system and a 9.4 Tesla cryomagnet (a magnet that operates a low temperatures) to increase sensitivity. The measurements are conducted using THz fields that use a unique waveguide-based THz signal generation and readout platform. In general, an EPR spectrometer yields detailed information on the geometric and electronic structure of molecular and solid-state materials. It is also used to obtain information about the lifetimes of free radicals, short-lived, highly reactive species involved in valuable chemical transformations as well as the initiation of possible pathological growth. These studies impact many areas, from the synthesis of inorganic and organic molecules to the development of new solid-state materials to compounds of magnetic and biological interest. Employing examples inspired from ongoing research, this instrument is an integral part of research and teaching at the undergraduate and graduate levels at MIT. It is also used by researchers at many collaborating institutions such as the University of California at Berkeley and the University of California at Davis.The new spectrometer has capabilities not yet available in any commercially available instrument. This EPR spectrometer supports research using steady-state THz EPR spectroscopy of molecular magnets and time-resolved THz EPR spectroscopy of transition metal photochemistry (UC Berkeley) and zero-field and high-field THz EPR of metalloproteins. It is also used to test heterometallic oxido models for oxygen-evolution reaction catalysts (UC Davis) and for studying quantum spin liquid state. The new spectrometer is essential to evaluate compounds that provide information on fractional spin excitations in a 1D Ising chain, where Ising represents a mathematical model of ferromagnetism used in statistical mechanics that allows the identification of phase transitions.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.