FIELD-DEPENDENT ISOTROPIC SHIFTS AND LIMITATIONS TO LINEWIDTHS IN SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE - A FLOQUET TREATMENT

Previously we have provided a quantitative theory that explains the ap parent field dependence observed for chemical shifts in high resolutio n solids state C-13 nuclear magnetic resonance spectroscopy (where mag ic angle spinning is combined with high-power H-1 decoupling). We have expanded that theoretical treatment so as to include the effect of ho monuclear dipole-dipole couplings among the abundant nuclear spin spec ies, and to the impact of off-resonance rf fields. These differing con tributions to the residual linewidths are assessed in a unified theore tical treatment using the Floquet theory for time-dependent Hamiltonia ns. Some comments are provided as to the circumstances in which the va rious contributing terms dominate. (C) 1996 American Institute of Phys ics.