Motional smearing of electrically recovered couplings measured from multipulse transients

The measurement of residual dipolar and quadrupolar coupling constants in t he liquid phase by using an electric held to destroy the isotropic nature o f molecular tumbling is complicated by charge-induced turbulent motion. In many cases this motion is due to charge injection at electrode surfaces, an effect that leads to an apparent removal of electrically recovered anisotr opic spectral splittings when measured from a spin-echo envelope modulation produced by a train of radio frequency (rf) pulses. To understand this ave raging, the effect of quadrupolar couplings and enhanced molecular diffusio n on free-induction, spin-echo, and Carr-Purcell signals is analytically de termined in the special case of homogeneous rf pulses. Additional signal da mping due to rf inhomogeneity and coupling constant heterogeneity is determ ined by numerically extending the kernel Formalism introduced by Herzog and Hahn to understand spin diffusion in solids. Finally, the merit of the num erical approach is tested by comparison vith analytical results for homogen eous rf pulses and experimental results for perdeuterated nitrobenzene invo lving inhomogeneous rf pulses and coupling heterogeneity. (C) 2001 John Wil ey & Sons, inc.