A method for efficient Hartmann-Hahn cross polarization unΓΊ 2) tends toward zero with increasing spinning frequency der rapid magic-angle sample spinning is presented. It combines (4, 5). Although the Hartmann-Hahn transfer at the exact rotor-synchronized amplitude modulation of one of the two spinsideband matching conditions v 1I 0 v 1S Γ
{v r or {2v r can lock radio-frequency fields for dipolar recoupling, with a slow be quite efficient, it is not well suited for practical applicaadiabatic amplitude variation to enhance the net polarization tions because of its sensitivity to RF field inhomogeneity transfer. The proposed scheme, called AMAP-CP, allows for cross and to the MAS frequency. polarization on the original Hartmann-Hahn matching condition A number of pulse sequences were proposed in the past v 1I Γ
v 1S . The polarization transfer is insensitive to chemical-shift to improve cross polarization under MAS conditions. They offsets, rotation frequency, and inhomogeneity of the radiofrepursue three goals: quency field. α§ 1997 Academic Press (i) Efficient polarization transfer at the original Hartmann-Hahn centerband matching condition v 1I Γ
v 1S . Ro-291