VARIABLE-EFFECTIVE-FIELD CROSS-POLARIZATION - AN APPROACH TO BROAD-BAND HARTMANN-HAHN MATCHING IN MAS NMR

A method for broadening the Hartmann-Hahn matching condition for cross polarization under magic angle spinning is presented. Variable-effect ive-field cross polarization (VEFCP) employs different effective radio -frequency (rf) fields on the H-1 channel during mixing, while the C-1 3 rf field remains constant. VEFCP is shown to result in both a broade r matching condition, and a more rapid polarization transfer than ordi nary cross polarization at the Hartmann-Hahn match. Experimental resul ts on both adamantane and polycarbonate are discussed.