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Pulse Sequences

CRAMPS

Abundant spin systems that experience homonuclear dipolar coupling (1H and 19F for example) tend to suffer from broad linewidths which can rarely be narrowed by MAS alone. Several special pulse sequences, or multiple pulse sequences as they are often referred to, have been developed to remove the effects of homonuclear dipolar coupling. The multiple pulse sequences employ phase-alternated pulses but leave behind the shielding anisotropy. By combining the multiple pulse sequences with MAS the so called CRAMPS experiment results. This technique removes the shielding anisotropy along with the homonuclear dipolar coupling and yields narrow isotropic spectra on the condition the rotation period is significantly longer than the multiple pulse cycle time. This experiment is not trivial to setup.

 

spectra 3The resolution in proton spectra of solids is improved by applying combined rotation and multiple-pulse spectroscopy (CRAMPS). Experiments performed by M. Monette (Bruker) with the 2.5 mm MAS probe.

January, 2006