Motional smearing of electrically recovered couplings measured from multipulse transients

Abstract

AbstractThe measurement of residual dipolar and quadrupolar coupling constants in the liquid phase by using an electric field to destroy the isotropic nature of 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 anisotropic spectral splittings when measured from a spin‐echo envelope modulation produced by a train of radio frequency (rf) pulses. To understand this averaging, the effect of quadrupolar couplings and enhanced molecular diffusion on free‐induction, spin‐echo, and Carr–Purcell signals is analytically determined in the special case of homogeneous rf pulses. Additional signal damping due to rf inhomogeneity and coupling constant heterogeneity is determined by numerically extending the kernel formalism introduced by Herzog and Hahn to understand spin diffusion in solids. Finally, the merit of the numerical approach is tested by comparison with analytical results for homogeneous rf pulses and experimental results for perdeuterated nitrobenzene involving inhomogeneous rf pulses and coupling heterogeneity. © 2001 John Wiley & Sons, Inc. Concepts Magn Reson 13: 171–189, 2001