EPR was used to determine the g-factor of composite ferrite materials, 2.203 is the free electron vibration. If the g-factor is less than / greater than the electron vibration. How to interpret EPR spectroscopy terms of its potential use.
The g-value of a free electron is 2.0023.
You need to find out g(parallel) and g (perpendicular) values in addition to A(parallel) and A(perpendicular) values. .Sometimes you may have to determine the gxy, gyz and gxz .If it is an isotropic signal, you will end up with only one value giso. Recording the spectrum both at RT and LNT provides more info about the nature of the compound. You should also remember, the free radicals exhibit sharp signals whereas the metal complexes exhibit broad peaks.
Electron spin resonance (ESR) or electron paramagnetic resonance (EPR) spectroscopy is widely used in the study of inorganic systems. Allows to obtain structural information. It has high sensitivity. (microM range) For an electron there are two possibilities of orientation in a magnetic field, parallel and antiparallel, g=hv/BH, g is dimensionless. The epr spectra contain very valuable information about the metallic site of the metallo-molecule. The number of different magnetic sites. The symmetry of the environment about the magnetic site. The ground state of the metal ion. The degree of electronic delocalization. The chemical nature of the ligands.
Factors that affect the epr signal or spin transition.
1. Interactions between nuclear spin and electronic spin. - Odd isotopes of the paramagnetic ion. I = nuclear spin (2I+1) signals. (hyperfine structure) Ex. Cu(II) I = 3/2 - Odd isotopes of the ligands. (superhyperfine structure) Ex. 15N, 31P (I=1/2)
2. Magnetic exchange interactions. nearby metal ions. Ex. dimers, trimers…
3. Distorted symmetries. Axial symmetry, g(perpendicular)= gx, gy; g(parallel)=gz, if hyperfine coupling, Axx=Ayy, Azz. Rhombic symmetry, gx, gy, gz, if hyperfine coupling, Axx, Ayy, Azz .
4. Splitting to zero field (A. S-O 2nd order).
What are the reasons behind the EPR signal shift toward a lower or higher magnetic field (B)?
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