ESR instrument composition Simplified Principle of Electron Spin Resonance (ESR) With an ESR instrument, a static magnetic field and microwaves are used to observe the behavior of the unpaired electrons in the material being studied. Electron paramagnetic resonance spectroscopy (EPR), also called electron spin resonance (ESR), is a technique used to study chemical species with unpaired electrons. It is stabilized against temperature fluctuation by immersion in an oil bath or by forced air cooling. Electron spin resonance (ESR) spectroscopy is a very powerful and sensitive method for the characterisation of the electronic structures of materials with unpaired electrons. 236-240 EPR spectroscopy is particularly useful for studying metal complexes or organic radicals. //--> The exact dimensions and material of the quartz EPR tube can be had from Ms. A. Varalakshmi (044 2257 4916) or (044 2257 5926). Electron spin resonance (ESR) spectroscopy is also known as Electron paramagnetic resonance (EPR) It is absorption spectroscopy similar to NMR, possible only with molecules having unpaired electrons Instead of Radiowaves in NMR, Microwaves is used in ESR. If the modulation is of low frequency (400 cycles/sec or less), the coils can be mounted outside the cavity and even on the magnet pole pieces. It is used in varying the power of the sample from the full power of klystron to one attenuated by a force 100 or more. The field should be stable and uniform over the sample volume.