ABSTRACT
Nuclear relaxation recovers the initial equilibrium state of spins excited by radiofrequency (RF) irradiation, thus allowing observation of a NMR signal. In other words, the frequency-and time-dependent data collected by pulse NMR experiments represent the same phenomenon. In spite of this, NMR applications are grouped under two separate categories: NMR spectrometry and NMR relaxation. The former is most popular among researchers who use NMR for structural analyses; however, even in this case, knowledge on the theory of nuclear relaxation is needed to perform even the simplest NMR experiments and to interpret the results. To emphasize the importance of this statement, it should be noted that the rst attempt, in 1936, to detect 1H and 7Li nuclei was unsuccessful because of the extremely long relaxation times. In addition, because nuclear relaxation affects the shapes of resonances and line widths in solutions and solids, an understanding of these effects is also necessary to avoid misinterpretations of NMR spectra. Relaxation studies can open the way not only to a deeper understanding of molecular dynamics via identication and characterization of motions on the large frequency scale but also to structural diagnostics via determination of interatomic distances and special relaxation criteria.
