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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Electron paramagnetic resonance | 6/7 | https://en.wikipedia.org/wiki/Electron_paramagnetic_resonance | reference | science, encyclopedia | 2026-05-05T10:04:27.171248+00:00 | kb-cron |
=== Electrochemistry applications === EPR is a very important technique in the electrochemical field because it operates to detect paramagnetic species and unpaired electrons. The technique has a long history of being coupled to the field, starting with a report in 1958 using EPR to detect free radicals generated via electrochemistry. In an experiment performed by Austen, Given, Ingram, and Peover, solutions of aromatics were electrolyzed and placed into an EPR instrument, resulting in a broad signal response. While this result could not be used for any specific identification, the presence of an EPR signal validated the theory that free radical species were involved in electron transfer reactions as an intermediate state. Soon after, other groups discovered the possibility of coupling in situ electrolysis with EPR, producing the first resolved spectra of the nitrobenzene anion radical from a mercury electrode sealed within the instrument cavity. Since then, the impact of EPR on the field of electrochemistry has only expanded, serving as a way to monitor free radicals produced by other electrolysis reactions. In more recent years, EPR has also been used within the context of electrochemistry to study redox-flow reactions and batteries. Because of the in situ possibilities, it is possible to construct an electrochemical cell inside the EPR instrument and capture the short-lived intermediates involved at lower concentrations than necessitated for NMR. Often, NMR and EPR experiments are coupled to get a full picture of the electrochemical reaction over time. It is also possible to determine the concentration of a specific radical species via EPR, as it is proportional to the double integral of the EPR signal as referenced to a calibration standard. A specific application example can be seen in Lithium ion batteries, specifically studying Li-S battery sulfate ion formation or in Li-O2 battery oxygen radical formation via the 4-oxo-TEMP to 4-oxo-TEMPO conversion. Other electrochemical applications to EPR can be found in the context of water purification reactions and oxygen reduction reactions. In water purification reactions, reactive radical species such as singlet oxygen and hydroxyl, oxygen, and hydrogen radicals are consistently present, generated electrochemically in the breakdown of water pollutants. These intermediates are highly reactive and unstable, thus necessitating a technique such as EPR that can identify radical species specifically.
=== Other applications === 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.
== High-field high-frequency measurements == High-field high-frequency EPR measurements are sometimes needed to detect subtle spectroscopic details. However, for many years the use of electromagnets to produce the needed fields above 1.5 T was impossible, due principally to limitations of traditional magnet materials. The first multifunctional millimeter EPR spectrometer with a superconducting solenoid was described in the early 1970s by Y. S. Lebedev's group (Russian Institute of Chemical Physics, Moscow) in collaboration with L. G. Oranski's group (Ukrainian Physics and Technics Institute, Donetsk), which began working in the Institute of Problems of Chemical Physics, Chernogolovka around 1975. Two decades later, a W-band EPR spectrometer was produced as a small commercial line by the German Bruker Company, initiating the expansion of W-band EPR techniques into medium-sized academic laboratories.
The EPR waveband is stipulated by the frequency or wavelength of a spectrometer's microwave source (see Table). EPR experiments often are conducted at X and, less commonly, Q bands, mainly due to the ready availability of the necessary microwave components (which originally were developed for radar applications). A second reason for widespread X and Q band measurements is that electromagnets can reliably generate fields up to about 1 tesla. However, the low spectral resolution over g-factor at these wavebands limits the study of paramagnetic centers with comparatively low anisotropic magnetic parameters. Measurements at
ν
{\displaystyle \nu }
40 GHz, in the millimeter wavelength region, offer the following advantages:
EPR spectra are simplified due to the reduction of second-order effects at high fields. Increase in orientation selectivity and sensitivity in the investigation of disordered systems. The informativity and precision of pulse methods, e.g., ENDOR also increase at high magnetic fields. Accessibility of spin systems with larger zero-field splitting due to the larger microwave quantum energy h
ν
{\displaystyle \nu }
. The higher spectral resolution over g-factor, which increases with irradiation frequency
ν
{\displaystyle \nu }
and external magnetic field B0. This is used to investigate the structure, polarity, and dynamics of radical microenvironments in spin-modified organic and biological systems through the spin label and probe method. The figure shows how spectral resolution improves with increasing frequency. Saturation of paramagnetic centers occurs at a comparatively low microwave polarizing field B1, due to the exponential dependence of the number of excited spins on the radiation frequency
ν
{\displaystyle \nu }
. This effect can be successfully used to study the relaxation and dynamics of paramagnetic centers as well as of superslow motion in the systems under study. The cross-relaxation of paramagnetic centers decreases dramatically at high magnetic fields, making it easier to obtain more-precise and more-complete information about the system under study. This was demonstrated experimentally in the study of various biological, polymeric and model systems at D-band EPR.
== Hardware components ==