Off resonance cross-polarization: A technique to reduce rf power requirements for magnetization transfer experiments in solids

Abstract

Cross-polarization of nuclei (I) with a low magnetogyric ratio is one of the pillars of many modern solid state NMR experiments, enhancing the sensitivity often by an order of magnitude. Cross-polarization is based upon cross-relaxation in the rotating frame between different nuclides, and occurs when the Hartmann-Hahn condition (2) is met. For magnetization transfer from spin Z to spin S, this condition requires radiofrequency fields, HI and Hs, applied simultaneously close to resonance for spin Z and spin S, respectively. H, and Hs must have the relation r&Jr = rsfk