BOUNDS ON SPIN DYNAMICS AND THE DESIGN OF MULTIPLE-PULSE NMR EXPERIMENTS

The ''universal bound on spin dynamics'' proposed by Sorensen is exami ned in detail and shown to be of great assistance in the design of nov el multiple-pulse NMR experiments. The efficiency of coherence transfe r between all possible states of a spin system, including populations, single-quantum coherences, and multiple-quantum coherences, is invest igated. Examples are drawn from coherence transfer processes in quadru polar coupled spin I=1 and 3/2 nuclei and weakly J coupled systems of two and three spin 1=1/2 nuclei. It is found that many of the most com monly used NMR pulse sequences fail to achieve the maximum coherence t ransfer efficiency when applied to spin I=3/2 or to three spin I=1/2 n uclei. However, it is shown that, with knowledge of the universal boun d, novel multiple-pulse NMR experiments that achieve optimal efficienc y can be easily derived using computer optimization. The application o f the universal bound to two-step coherence transfer experiments prese nts a number of conceptual difficulties. In particular, examples are p resented where the product of the universal bounds on the two individu al coherence transfer coefficients is larger than the universal bound on the overall transfer from the initial to the final state. These dif ficulties are resolved and explained in terms of the presence of a ''r esidue'' that is created together with the intermediate state. The uni versal bound is used to examine the conditions under which the effect of this residue can be suppressed and the constraints that this places on the design of optimal multi-step coherence transfer NMR experiment s. (C) 1997 American Institute of Physics.