NMR Pulse Sequence
Nuclear magnetic resonance: precession, RF pulse, FID, and Fourier spectrum
NMR Physics: Proton spins align along B₀ (z-axis) with Larmor frequency ω₀ = γB₀ (γ_H = 42.577 MHz/T). A 90° RF pulse at ω₀ tips magnetization into the xy-plane. Spins then precess while dephasing with time constant T2* (inhomogeneous broadening) → Free Induction Decay (FID). The Fourier transform of the FID gives the NMR spectrum. T1 is the longitudinal (spin-lattice) relaxation back to equilibrium. The peak frequency encodes chemical shift → molecular structure.