Efficient double-quantum excitation in rotational resonance NMR.

Abstract We present a new technique for double-quantum excitation in magic-angle-spinning solid-state NMR. The method involves (i) preparation of nonequilibrium longitudinal magnetization; (ii) mechanical excitation of zero-quantum coherence by spinning the sample at rotational resonance, and (iii) phase-coherent conversion of the zero-quantum coherence into double-quantum coherence by frequency-selective spin inversion. The double-quantum coherence is converted into observable magnetization by reversing the excitation process, followed by a π/2 pulse. The method is technically simple, does not require strong RF fields, and is feasible at high spinning frequencies. In [ 13 C 2 , 15 N]-glycine, with an internuclear 13 C– 13 C distance of 0.153 nm, we achieve a double-quantum filtering efficiency of ≃56%. In [11,20– 13 C 2 ]-all- E -retinal, with an internuclear 13 C– 13 C distance of 0.296 nm, we obtain ≃45% double-quantum filtering efficiency.