Abstract: Very recently, Frydman et al. have shown that the combined use of MAS and two-dimensional multiple-quantum (MQ) spectroscopy can refocus the second-order anisotropic effects of half-in-teger quadrupoles. The present paper discusses theoretical aspect of this novel 2D MQ MAS method through evaluating the propagation of density matrices evolving under the effects of noncommuting time-dependent Hamiltonians. The influence of radiofrequency pulse excitation and conversion on the intensities in the spectra is analyzed and the conditions that maximize the MQ MAS signal for a spin-3/2 are obtained. Numerical simulation of the 2D experimental spectrum of ²³Na of Na₂C₂O₄ shows that the quadrupolar coupling parameters and the isotropic chemical shift can be determined.

Key words: Half-integer quadrupolar nuclei, Two-dimensional multiple-quantum NMR, Na₂C₂O₄, Numerical simulation