Spin Counting with Fast MAS

A novel magic angle spinning (MAS) multiple-quantum spin counting experiment based on the C7 recoupling sequence of Leeet al.is described. In contrast to previous approaches the new experiment is applicable at fast MAS rates and can be used to follow the multiple-quantum excitation dynamics with fine time resolution. The new method is illustrated by experiments on adamantane at spinning speeds comparable to the nonspinning dipolar linewidth. The sizes of the clusters of dipolar-coupled spins measured using the new experiment are compared to those obtained using the original nonspinning spin counting technique of Baumet al.