APPLICATION OF ROTOR-SYNCHRONIZED AMPLITUDE-MODULATED CROSS-POLARIZATION IN A C-13-H-1 SPIN PAIR UNDER FAST MAGIC-ANGLE-SPINNING

Rotor-synchronized amplitude-modulated Hartmann-Hahn crosspolarization has been applied under fast magic-angle spinning to a powder sample o f ferrocene. The influence on the cross-polarization process of the he teronuclear double quantum (flop-flop) transitions induced by the ampl itude modulation for low ratios of the radiofrequency-field strength t o the spinning speed is studied in details. The experimental data are in good agreement with theoretical calculations for a two-spin 1/2 sys tem, although the intensity of the double quantum transitions is obser ved to be significantly smaller than expected. Moreover, it is shown t hat an efficient polarization transfer at the Hartmann-Hahn centerband matching condition as well as a broadening of the matching conditions is obtained by an appropriate partial scaling of the effective radiof requency fields which minimizes the destructive effect of double quant um cross-polarization. (C) 1998 Academic Press.