Difference between revisions of "Electron Spin Resonance (ESR)"

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=== Background ===
=== Background ===
[[Image:Epr splitting.png|thumb|300px|Increasing magnetic field causes the spin states of electrons to be split ]]
'''Electron Spin Resonance''' (ESR) also known as Electron Paramagnetic Resonance (EPR) spectroscopy or electron paramagnetic resonance spectroscopy is a technique for studying chemical species that have one or more unpaired electrons such as free radicals, odd electron molecules, transition metal complexes, lanthanide ions, and triplet state molecules. It is analogous to NMR except it deals with spins of electrons rather than the spins of atomic nuclei. It is most useful in studying free radicals or organic complexes having transition metal ions since most stable molecules have all their electrons paired. Most ESR spectra are recorded and published as first derivatives of the original signal.


'''Electron Spin Resonance''' (ESR) also known as Electron Paramagnetic Resonance (EPR) spectroscopy or electron paramagnetic resonance spectroscopy is a technique for studying chemical species that have one or more unpaired electrons. It is analogous to NMR except it deals with spins of electrons rather than the spins of atomic nuclei. It is most useful in studying free radicals or organic complexes having transition metal ions since most stable molecules have all their electrons paired. Most ESR spectra are recorded and published as first derivatives of the original signal.
=== Significance ===
In a standard ESR experiment, the sample is irradiated with the microwave field at the constant frequency (~10GHz), the external magnetic field is slowly changed. Electron spins  align with the field, but also can precess around the equilibrium orientation
 
The frequency of the spin precession depends on the field, it increases (linearly in a simple case) with the field increasing. When the field passes through the point, where the spin precession frequency corresponds to the microwave frequency applied, the sample will absorb microwave radiation.
 
In pulsed ESR a strong burst of microwave energy is applied and a complex response signal or transient signal is recorded. This is analyzed through fourier transform to yield an ESR spectrum in the frequency domain.


=== Significance ===
In ESR a sample is placed in magnetic field which forces the unpaired electrons to orient their spin with the field. An RF field oriented perpendicular to the magnetic field temporarily aligns the electron spin off from the magnetic axis. When the RF field is stopped the electron relaxes relatively slowly back to the original field orientation. The relaxation causes a RF signal which can be detected with a pickup coil that is orthogonal to the excitation coil. The signal includes a number of frequencies reflecting the various locations unpaired electrons in the molecule. These frequencies can be deconvolved with fourier transform to show distinct peaks.


<div id="Flash">ESR animation</div> <swf width="500" height="400">images/2/21/Esr.swf</swf>
<div id="Flash">ESR animation</div> <swf width="500" height="400">images/2/21/Esr.swf</swf>


=== Operation ===
=== Operation ===
{{#ev:youtube|CYVaTsqMWII}}
{{#ev:youtube|KOnodnj8a_8}}
 
<embed_document width="100%" height="400">images/6/68/Esr.pdf</embed_document>


=== External Links ===
=== External Links ===
see [[wikipedia:Electron_paramagnetic_resonance]]
[[wikipedia:Electron_paramagnetic_resonance]]
 
[http://web.nmsu.edu/~snsm/classes/chem435/Lab7/ NMSU Spectroscopy Lab]
 
[http://www.bruker-biospin.com/cw.html Bruker ESR explanation]

Latest revision as of 10:52, 8 November 2011

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Background

Increasing magnetic field causes the spin states of electrons to be split

Electron Spin Resonance (ESR) also known as Electron Paramagnetic Resonance (EPR) spectroscopy or electron paramagnetic resonance spectroscopy is a technique for studying chemical species that have one or more unpaired electrons such as free radicals, odd electron molecules, transition metal complexes, lanthanide ions, and triplet state molecules. It is analogous to NMR except it deals with spins of electrons rather than the spins of atomic nuclei. It is most useful in studying free radicals or organic complexes having transition metal ions since most stable molecules have all their electrons paired. Most ESR spectra are recorded and published as first derivatives of the original signal.

Significance

In a standard ESR experiment, the sample is irradiated with the microwave field at the constant frequency (~10GHz), the external magnetic field is slowly changed. Electron spins align with the field, but also can precess around the equilibrium orientation

The frequency of the spin precession depends on the field, it increases (linearly in a simple case) with the field increasing. When the field passes through the point, where the spin precession frequency corresponds to the microwave frequency applied, the sample will absorb microwave radiation.

In pulsed ESR a strong burst of microwave energy is applied and a complex response signal or transient signal is recorded. This is analyzed through fourier transform to yield an ESR spectrum in the frequency domain.


ESR animation

<swf width="500" height="400">images/2/21/Esr.swf</swf>

Operation

<embed_document width="100%" height="400">images/6/68/Esr.pdf</embed_document>

External Links

wikipedia:Electron_paramagnetic_resonance

NMSU Spectroscopy Lab

Bruker ESR explanation

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