NMR CROSS-POLARIZATION BY ADIABATIC PASSAGE THROUGH THE HARTMANN-HAHNCONDITION (APHH)

It is shown that the heteronuclear cross-polarization efficiency in th e rotating frame can be improved by sweeping the radio-frequency ampli tude adiabatically through the Hartmann-Hahn condition. The enhancemen t is particularly significant for strongly coupled IS spin systems wit h weak dipolar coupling to extraneous spins. A good approximation to a n adiabatic transfer is obtained with a tangential time dependence of the radiofrequency field amplitude whereby transient oscillations are efficiently suppressed.