Multipulse NMR part II. Product operator description of the weakly coupled, two-spin-� system

Abstract

This is Part II of a short introduction to multipulse NMR. On the basis of the results obtained in Part I (Concepts Magn. Reson., 1996, 8, 17–32) for single‐spin systems, the product operator formalism for the weakly coupled two‐spin‐½ system is described. The equilibrium, pulse effect, and the evolution of the density operator during free precession are considered. Special attention is paid to evolution under the action of the coupling Hamiltonian. It is shown that radio frequency pulses acting on the two‐spin system can create unobservable multiple‐quantum coherences. The spin‐echo pulse sequence and decoupling are treated in terms of product operator formalism. The limitations of the classical approach in describing coupled spins are discussed. © 1997 John Wiley & Sons, Inc.