Analysis of multiple-pulse-based heteronuclear J cross polarization in liquids

Abstract

Classical heteronuclear J cross polarization in liquids utilizing two CW RF fields has largely been replaced by pulse-interrupted free-precession methods because of difficulties in obtaining a Hartmann-Hahn match of the two fields within the size ofthe heteronuclear J coupling. Here previously suggested contact schemes are investigated in which both nuclei are subjected to sequences of simultaneous RF pulses. It is shown both experimentally and computationally that efficient cross polarization in liquids over a wide range of RF field mismatches can be obtained with these methods, and nonideal behavior is analyzed. Experimental results show that multiple-pulse-based J-cross-polarization spectra compare favorably in sensitivity, phase, and enhancement distribution with those obtained from pulse-interrupted free-precession methods. It is also shown that concurrent homonuclear/heteronuclear Hartmann-Hahn transfer can be achieved over a very wide bandwidth with these sequences.