Typical Experimental Methods for Studying NMR Relaxation

Abstract

From a methodological point of view, nuclear magnetic relaxation refers to a whole family of different techniques for probing the equilibration processes of nuclear magnetization. This includes the common radiofrequency pulse sequences for perturbing the thermal equilibrium and detecting the relaxation process. Special variants, such as field-cycling NMR relaxometry and rotating-frame methods, are also discussed with respect to their experimental limits and application ranges. In complex systems, which are of particular interest in the context of this book, motional averaging of secular dipolar interactions is often incomplete. This is due to relatively slow components of molecular dynamics. They can be studied based on unaveraged but nevertheless slowly fluctuating secular spin couplings in a way that is complementary to the ordinary spin–lattice relaxation techniques. The extraordinarily wide time or frequency ranges to which the techniques are sensitive in combined form are compared in a tabular scheme.