Topic overview

Start with the big picture

NMR and ESR begin with non-zero spin, which gives nuclei or electrons a magnetic moment. An external magnetic field splits spin energy levels, and the population difference between them contributes to the observable signal. Resonant radiation drives transitions at the Larmor frequency; precessing net magnetization induces a voltage that is recorded as a free induction decay. Processing this time-domain signal by Fourier transform produces a frequency-domain spectrum. Spectral interpretation draws on chemical shift, scalar coupling, relaxation, and—in ESR—interactions such as dipolar coupling, g-anisotropy, and hyperfine coupling. The broader topic also connects pulse sequences, magic-angle spinning, and instrument tuning to signal acquisition and quality.