where K is the exchange superoperator and is the superoperator describing chemical shift evolution and relaxation. The NOESY pulse sequence is designed to select z-magnetization that is present in the mixing time τ m . In conventional applications of the experiment, inphase cross-peaks are generated as a result of chemical exchange of z magnetization during the mixing time, and the experiment thus creates a readily interpreted map of the propagator e Kτm for the exchange superoperator.