Electron Spin Resonance Spectroscopy:

As discussed earlier, the basis of EPR lies in the spin of an electron and its associated magnetic moment. When an electron is placed within an applied magnetic field, the two possible spin states of the electron have different energies. The lower energy state occurs when the magnetic moment of the electron, μ, is aligned with the magnetic field and a higher energy state occurs where μ is aligned against the magnetic field.

Therefore, the energy state of the electron can be defined as .

Figure 36.02: The schematic of energy level at different applied magnetic field.

From this relationship, there are two important factors to be noted: (i) the two spin states have the same energy when there is no applied magnetic field and (ii) the energy difference between the two spin states increases linearly with increasing magnetic field strength as shown in Figure 36.02.