Electron Paramagnetic Resonance (EPR, ESR) Spectroscopy


Introduction

When an atom or molecule with an unpaired electron is placed in a magnetic field, the spin of the unpaired electron can align either in the same direction or in the opposite direction as the field. These two electron alignments have different energies and application of a magnetic field to an unpaired electron lifts the degeneracy of the 1/2 spins of the electron.

Electron-paramagnetic-resonance (EPR) or electron-spin-resonance (ESR) spectroscopy measures the