EPR spectroscopy key principles

Electron paramagnetic resonance (EPR) spectroscopy is really in a very primitive state compared with NMR spectroscopy even though the bedrock principles are in fact very similar  

The electron spin quantum number also defines the number of allowed spin states that may exist. This number is equivalent to 27e + 1- In the case of the electron, is 1/2 therefore there are only two allowed spin states that are initially degenerate. Since spin angular momentum is quantised in terms of magnitude and orientation according to the electron spin quantum number, 7e then z-axis components of angular momentum // are similarly quantised. Each allowed z-axis component is represented by an individual magnetic spin quantum number, ms, according to 

The inherent magnetic field strength associated with any given electron spin state is represented by a electron magnetic moment, /x , that is proportional to / according to 

The energy differences between different spin states are created by the differential way in which the magnetic moments of given spin states interact with the applied magnetic field, The interaction energy attributable to either spin state Em, is defined by the product 

In comparison with most nuclei, the g-factor is positive but the ratio /e is negative. Hence the magnetic moment fj l is positive for the p state and negative for the a state according to 

---