MULTIPULSE NMR .2. PRODUCT OPERATOR DESCRIPTION OF THE WEAKLY COUPLED, 2-SPIN-1 2 SYSTEM/

This is Part II of a short introduction to multipulse NMR. On the basi s of the results obtained in Part I (Concepts Magn. Reson., 1996, 8, 1 7-32) for single-spin systems, the product operator formalism for the weakly coupled two-spin-1/2 system is described. The equilibrium, puls e effect, and the evolution of the density operator during free preces sion are considered, Special attention is paid to evolution under the action of the coupling Hamiltonian. It is shown that radio frequency p ulses acting on the two-spin system can create unobservable multiple-q uantum coherences. The spin - echo pulse sequence and decoupling are t reated in terms of product operator formalism. The limitations of the classical approach in describing coupled spins are discussed. (C) 1997 John Wiley & Sons, Inc.