Multiple-quantum relaxation in the magic-angle-spinning NMR of 13C spin pairs,

T. Karlsson, A. Brinkmann, P. J. E. Verdegem, J. Lugtenburg, and M. H. Levitt,
Solid-State NMR 14, 43-58, (1999).
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We determine the decay rate constants of zero-, double- and single-​quantum coherence for 13C2 spin pairs in magic-​angle-​spinning solid-​state NMR. The double-​quantum coherence is excited by a C7 pulse sequence and converted into zero-​quantum coherence by a frequency-​selective pair of π/2 pulses. The zero-​quantum coherence is reconverted into observable magnetization by a second pair of π/2 pulses followed by a second C7 sequence. In a magnetically dilute system where the 13C–13C distance is 0.296 nm, the relaxation rate constants are consistent with a model of uncorrelated random fields at the two labeled 13C sites. In a fully-​labelled system with a short 13C–13C distance of 0.153 nm, the measured rate constants are inconsistent with the uncorrelated random field model.