Multiple-Quantum Cross Polarization in Quadrupolar Spin Systems during Magic-Angle Spinning

摘要

We describe the concept of multiple-quantum cross polarization (CP) between an I=3/2 and an I=1/2 spin during magic-angle spinning. Experimental and theoretical results for ~(23)Na-~(1)H pairs are presented that elucidate the transfer mechanism and the beneficial effect of adiabatic amplitude modulations of the CP field. The multiple-quantum CP approach is shown to be beneficial for improving the sensitivity of CP-MQMAS experiments and for detecting dipolar correlations.