## Electron paramagnetic resonance |

**Electron paramagnetic resonance** (**EPR**) or **electron spin resonance** (**ESR**) ^{[1]}^{[2]} and was developed independently at the same time by

- theory
- spectral parameters
- applications
- high-field high-frequency measurements
- hardware components
- pulsed electron paramagnetic resonance
- see also
- references
- external links

Every electron has a

where

- is the electron's so-called
(see also the*g*-factorLandé ), for the free electron,*g*-factor^{[3]} - is the
Bohr magneton .

Therefore, the separation between the lower and the upper state is for unpaired free electrons. This equation implies that the splitting of the energy levels is directly proportional to the

An unpaired electron can move between the two energy levels by either absorbing or emitting a

Experimentally, this equation permits a large combination of frequency and magnetic field values, but the great majority of EPR measurements are made with microwaves in the 9000–10000 MHz (9–10 GHz) region, with fields corresponding to about 3500

For the microwave frequency of 9388.2 MHz, the predicted resonance occurs at a magnetic field of about = 0.3350 teslas = 3350 gausses.

Because of electron-nuclear mass differences, the ^{1}H nuclei. (For NMR spectroscopy, the corresponding resonance equation is where and depend on the nucleus under study.)

As previously mentioned an EPR spectrum is usually directly measured as the first derivative of the absorption. This is accomplished by using field modulation. A small additional oscillating magnetic field is applied to the external magnetic field at a typical frequency of 100 kHz.^{[4]} By detecting the peak to peak amplitude the first derivative of the absorption is measured. By using phase sensitive detection only signals with the same modulation (100 kHz) are detected. This results in higher signal to noise ratios. Note field modulation is unique to continuous wave EPR measurements and spectra resulting from pulsed experiments are presented as absorption profiles.

In practice, EPR samples consist of collections of many paramagnetic species, and not single isolated paramagnetic centers. If the population of radicals is in thermodynamic equilibrium, its statistical distribution is described by the

where is the number of paramagnetic centers occupying the upper energy state, is the

The sensitivity of the EPR method (i.e., the minimal number of detectable spins ) depends on the photon frequency according to

where is a constant, is the sample's volume, is the unloaded

A great sensitivity is therefore obtained with a low detection limit and a large number of spins. Therefore, the required parameters are:

- A high spectrometer frequency to maximize the Eq. 2. Common frequencies are discussed
below - A low temperature to decrease the number of spin at the high level of energy as shown in Eq. 1. This condition explains why spectra are often recorded on sample at the
boiling point ofliquid nitrogen orliquid helium .

Other Languages

العربية: رنين مغناطيسي إلكتروني

беларуская: Электронны парамагнітны рэзананс

беларуская (тарашкевіца): Электронны парамагнітны рэзананс

български: Електронно-спинов резонанс

bosanski: Elektronska spinska rezonanca

dansk: Elektronspinresonans

Deutsch: Elektronenspinresonanz

español: Resonancia paramagnética electrónica

فارسی: تشدید پارامغناطیسی الکترون

français: Résonance paramagnétique électronique

Gaeilge: Athshondas paramaighnéadach

한국어: 전자 스핀 공명

hrvatski: Elektronska paramagnetska rezonancija

italiano: Risonanza paramagnetica elettronica

עברית: תהודה מגנטית אלקטרונית

ქართული: ელექტრონული პარამაგნიტური რეზონანსი

қазақша: Электрондық парамагниттік резонанс

magyar: Elektronspin-rezonancia

Nederlands: Elektronspinresonantie

日本語: 電子スピン共鳴

norsk nynorsk: Elektronspinnresonans

polski: Spektroskopia EPR

română: Rezonanță electronică de spin

русский: Электронный парамагнитный резонанс

српски / srpski: Elektronska paramagnetna rezonancija

srpskohrvatski / српскохрватски: Elektronska paramagnetna rezonanca

svenska: Elektronspinnresonans

татарча/tatarça: Электрон парамагнит резонансы

Türkçe: Ferromanyetik rezonans

українська: Електронний парамагнітний резонанс

中文: 電子自旋共振