In atomic, molecular, and solid-state physics, the electric field gradient (EFG) measures the rate of change of the electric field at an atomic nucleus generated by the electronic charge distribution and the other nuclei. The EFG couples with the nuclear electric quadrupole moment of quadrupolar nuclei (those with spin quantum number greater than one-half) to generate an effect which can be measured using several spectroscopic methods, such as nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR, ESR), nuclear quadrupole resonance (NQR), M?ssbauer spectroscopy or perturbed angular correlation (PAC).
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