[ citation needed ] [18], In the field of quantum computing, pulsed EPR is used to control the state of electron spin qubits in materials such as diamond, silicon and gallium arsenide. One can then measure the emitted microwave signal which is created by the sample magnetization. Resonance means the cavity stores microwave energy and its ability to do this is given by the quality factor Q, defined by the following equation: Q=2π(energy stored)(energy dissipated){\displaystyle Q={\frac {2\pi ({\text{energy stored}})}{({\text{energy dissipated}})}}}, The higher the value of Q the higher the sensitivity of the spectrometer. EPR/ESR spectroscopy can be applied only to systems in which the balance between radical decay and radical formation keeps the free radicals concentration above the detection limit of the spectrometer used. NMR Nuclear Magnetic Resonance (NMR) Spectroscopy is the resonance that occurs when a charged nucleus is placed in a magnetic field and is ‘swept’ by a radio frequency that causes the nuclei to ‘flip’. It is currently practiced in a variety of modalities, mainly in the areas of biophysics and heterogeneous catalysis. Electron spin resonance (ESR) spectroscopy, invented by Zavoiskii in 1944, is similar to NMR spectroscopy. Eaton, S.S. Eaton, in Comprehensive Coordination Chemistry II, 20032.2.1 Introduction Electron paramagnetic resonance (EPR) spectroscopy, also called electron spin resonance (ESR) or electron magnetic resonance (EMR) measures the absorption of microwaves by paramagnetic centers with one or more unpaired electrons. High-field high-frequency EPR measurements are sometimes needed to detect subtle spectroscopic details. EPR was first observed in Kazan State University by Soviet physicist Yevgeny Zavoisky in 1944, [1] [2] and was developed independently at the same time by Brebis Bleaney at the University of Oxford. EPR/ESR spectroscopy has been used to measure properties of crude oil, in particular asphaltene and vanadium content. We will start with a synopsis of the fundamentals of ESR spectroscopy. [ citation needed ]. This results in a change of impedance which serves to stop the cavity from being critically coupled. … 2. [ citation needed ], EPR/ESR also has been used by archaeologists for the dating of teeth. can therefore be detected by ESR. Molecular compounds that contain one or more unpaired electrons are paramagnetic. When the magnetic field strength is such that an absorption event occurs, the value of Q will be reduced due to the extra energy loss. For further details on the theory and practice of ESR spectroscopy, refer to one of the excellent texts on ESR spectroscopy [2-9]. as microwave sources in reflection cavity homodyne spectrometers, and as marginal oscillators in which the oscillator cavity (a TE 011 cylindrical cavity) is the observing cavity. In crystals, the number of EPR lines is determined by the number of crystallographically equivalent orientations of the EPR spin (called "EPR center"). 20 tesla, the frequency is similar to VHF and UHF television broadcasts (60–1000 MHz). An example of this work is the study of radical reactions in single crystals of amino acids exposed to x-rays, work that sometimes leads to activation energies and rate constants for radical reactions. Magnetochemistry is concerned with the magnetic properties of chemical compounds. A simulation of the observed EPR spectrum is shown at the right and agrees with the 12-line prediction and the expected line intensities. 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