Trains of short pulses in the manner of ‘delays alternating with nutations for tailored excitation’ (DANTE) have been applied to the Pake patterns of protons of water molecules trapped in a static powdered sample of barium chlorate monohydrate. The spin dynamics in the course of such experiments have been investigated by means of numerical simulations and compared with the ideal refocusing that can be achieved under magic-angle spinning (MAS). Solid echoes yield essentially undistorted lineshapes, in contrast to direct excitation without refocusing that leads to severe dispersions of the phases because of inhomogeneous interactions such as homonuclear dipolar couplings and anisotropic chemical shifts. The selectivity of DANTE sequences allows one to access ‘slices’ of the Pake pattern that can be related to particular crystallite orientations. Single-crystal spectra can therefore be extracted from powder spectra. A similar behavior is expected for both dipolar and quadrupolar echoes.
Dedicated to: Kev Salikhov on the occasion of his 80th birthday.
This work was supported by the Swiss National Science Foundation (SNSF), the Ecole Polytechnique Fédérale de Lausanne (EPFL), the University of Neuchâtel, the Neuchâtel Platform of Analytical Chemistry (NPAC), the Swiss Commission for Technology and Innovation (CTI) and the European Research Council (ERC, project ‘Dilute para-water’).
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