Electric field NMR  Electric field NMR (EFNMR) spectroscopy differs from conventional NMR spectroscopy in that a sample containing suitable nuclei is polarised by a strong dc electric field instead of a constant magnetic field. The nuclei are stimulated (perturbed) by means of an alternating magnetic field, generated by passing an alternating current through a set of coils. The resulting magnetic resonance signal is small, and as in conventional NMR is typically sensed using a second set of coils and an amplifier. The shifting and splitting of spectral lines of atoms and molecules due to the presence of an external static electric field is referred to as the Stark effect.