electron spin resonance
Experimental set-up for measuring electron spin resonance.
Electron spin resonance (ESR) is a method of studying the structure of molecules by finding the positions of electrons within them.
ESR is a spectrographic technique and is applicable only to paramagnetic substances (see paramagnetism). Hence it is also known as paramagnetic resonance (EPR). It locates unpaired electrons by their spin and by the way they align themselves in an external magnetic field when the molecule absorbs microwave radiation.