Spin counting with fast MAS

A novel magic angle spinning (MAS) multiple-quantum spin counting experimen t based on the C7 recoupling sequence of Lee et al. is described. In contra st to previous approaches the new experiment is applicable at fast MAS rate s and can be used to follow the multiple-quantum excitation dynamics with f ine time resolution. The new method is illustrated by experiments on adaman tane at spinning speeds comparable to the nonspinning dipolar linewidth. Th e sizes of the clusters of dipolar-coupled spins measured using the new exp eriment are compared to those obtained using the original nonspinning spin counting technique of Baum et al. (C) 1999 Academic Press.