Localized cross-polarization in solids

Abstract

Single quantum heteronuclear cross-polarization in solids is strongly sensitive to resonance offsets. In the presence of main field- or radio-frequency field gradients, the cross-polarization efficiency, therefore, shows a strong spatial dependence, which represents a new principle for localized NMR in solids. Since slices-selective excitation is achieved simultaneously to cross-polarization, the suggested pulse sequences avoid the use of shaped pulses, the application of which is problematic with solid. The dependence of the localization efficiency on experimental and sample parameters is analyzed theoretically for a spin-1/2 system in the presence of a static or a radio-frequency magnetic field gradient. The resulting slice profiles and the calculated dependence of the slice thickness on the parameters of the basic cross-polarization procedures are discussed and confirmed experimentally on the example of1H-3C spin systems.