Two-frequency imaging method for multi-level quadrupole systems

An encoding procedure for two-dimensional rotating-frame imaging and positional spectroscopy in quadrupole systems with spin I> 3/2 is reported. The technique consists of a two-frequency irradiation pulse sequence: The population of a pair of spin states is changed by a radiofrequency pulse with a linear gradient and a second transition, which involves one of the two affected states, is excited with a second pulse with a gradient perpendicular to the first one. The spatial-spin distribution in the plane defined by the orthogonal radiofrequency gradients is recorded on Cartesian coordinates. The theoretical description of the technique and experimental results demonstrating its applicability to a powder sample containing I = 7/2 nucleus are given.