ABSTRACT
Nuclear magnetic resonance (NMR) spectroscopy deals with the interactions among nuclear magnetic moments (nuclear spins) and between the spins and their environment in the presence of a static magnetic field B0, probed by radiofrequency (RF) fields. The couplings involving the spins are relatively weak which results, in particular in low-viscosity liquids, in narrow lines and spectra with a rich structure. The NMR experiments are commonly carried out in the time domain: the spins are manipulated by sequences of RF pulses and delays, creating various types of non-equilibrium spin state, and the NMR signal corresponding to magnetization components perpendicular toB0 is detected as a function of time (the free induction decay, FID). In terms of the kinetics, the weakness of the interactions results in slow decays (typically milliseconds to seconds) of non-equilibrium states. The recovery processes taking the ensembles of nuclear spins back to equilibrium and some related phenomena, are called nuclear spin relaxation. The relaxation behaviour of nuclear spin systems is both an important source of information about the molecular structure and dynamics and a factor to consider in optimizing the design of experiments.
