Mapping molecular orientation in solids by rotating-frame NQR techniques

A multi-dimensional NQR technique to image both the spatial distribution of quadrupolar nuclei and the local orientation of the electric field gradient tensor at the quadrupole sites in solids is reported. The encoding procedure is based on the irradiation of the sample by a pulse sequence composed of spatially homogeneous and inhomogeneous radiofrequency fields. A method that encodes the spatial and orientation information in the amplitudes of the free-induction decay signals and a proper three-dimensional reconstruction procedure that yields the space-orientation-dependent NQR spectra are described. A two-dimensional variant allows rapid measurement of the spatially dependent orientation distribution of molecules, disregarding the spectroscopic information. Copyright 1998 Academic Press.