Abstract

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.