MRI: Development of a broadband terahertz electron paramagnetic resonance spectrometer

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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.