CROSS POLARIZATION UNDER FAST MAGIC ANGLE SPINNING - THERMODYNAMICAL CONSIDERATIONS

Thermodynamic aspects of cross polarization under fast magic angle sample spinning are studied. An extension of the static cross-polarization model is presented which applies to the "sidebands" of the Hartmann-Hahn condition. The cross-polarization process for the "sidebands" is not spin-energy conserving but energy is supplied or adsorbed by the sample rotation. For a static sample, cross polarization proceeds through heteronuclear zero-quantum transitions. For a rotating sample, zero-quantum as well as double-quantum cross polarization is observed experimentally. This behavior is explained by the extended model.