ESR Spectra-Guided TEXT
19.1. ELECTRONIC ENERGY LEVEL OF THE ODD ELECTRON
Electron Spin Resonance-ESR spectra, recorded using suitable microwave and varying magnetic field, is shown by molecules, ions, or atoms possessing unpaired electrons.
The figure in the following file (File-1) shows the electronic energy level of the odd electron (unpaired electron) in the presence of suitable microwave and varying magnetic field.
19.2. NUCLEAR HYPER-FINE SPLITTING
The Energy levels of an odd electron are further splinted by the nuclear spin. The following file (File-2) gives an account of the ESR spectrum of hydrogen atom due to nuclear splitting of hydrogen nucleus.
19.3. PRESENTATION OF THE ESR SPECTRUM:
The following file (File-3) gives the picture of typical ESR spectrum as Intensity I against the strength of the applied field as derivative curves.
File-3 Presentation of ESR spectrum
19.4. HYPER-FINE SPLITTING INVOLVING MORE THAN ONE NUCLEUS.
A nucleus with nuclear spin, I can take any of the 2I+1 values corresponding to the quantum numbers –I, -I+1, I-1, I, These orientations give rise to 2I+1 different nuclear energy states. This concept if explained in File-4 using Methyl radical
19.5. ANISOTROPY ‘g’ VALUE
For radicals with lower symmetry, anisotropic effects are manifested in the solid spectra for both the I values and the values. Usually for these lower symmetry systems, the solution spectra qualitatively appear as isotropic spectra because the anisotropic effects are averaged to zero by the rapid rotation of the molecule.File-5
19.6. NUCLEAR QUADRUPLE INTERACTION
A nucleus that has a nuclear spin quantum number I>1 also has as electric moment, and the unpaired electron interacts with both the nuclear magnetic and electric moments. The electric field gradient at the nucleus can interact with the quadruple moment as in NQR, and this interaction affects the electron spin energy states via the nuclear – electronic magnetic coupling as a second order perturbation as explained in File-6.
19.7. APPLICATIONS OF ESR SPECTROSCOPY
The ESR spectral applications to some typical atoms, molecule or ion are given in File-7 attached below.
19.8. PROBLEMS in ESR
The following file (File-8) gives a list of illustrated numerical problems related to ESR
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