DETERMINATION OF THE SYMMETRY OF THE ELECTRIC-FIELD GRADIENT TENSOR FOR SPIN-3 2 NUCLEI IN POLYCRYSTALLINE 2,4,6-TRICHLORO-1,3,5-TRIAZINE BY 2-DIMENSIONAL NUTATION FT MAXIMUM-ENTROPY METHOD NQR SPECTROSCOPY/

An approach for the evaluation of the asymmetry parameter, eta, of the electric field gradient tenser for spin-3/2 systems from two-dimensio nal nutation spectroscopy using the maximum entropy method (MEM) is pr esented. The superiority of the MEM over the traditional fast Fourier transform (FFT) method is demonstrated in NQR spectral analysis of two -dimensional (2D) data. A comparison of the theoretically simulated 2D spectrum (FFT and MEM) with that recorded experimentally is shown to permit the evaluation of eta with improved sensitivity. Use of the MEM in 2D-NQR spectroscopy can lead to sensitivity improvements, reductio n of instrumental artefacts and truncation errors, shortened data acqu isition times and automatic suppression of noise, while at the same ti me increasing the resolution. The method has been successfully demonst rated for the two Cl-35 sites in polycrystalline 2,4,6-trichloro-1,3,5 -triazine (cyanuric chloride).