Echo or antiecho optimization with MQMAS sequence in solid-state MAS NMR using a JDK1.3 applet

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Introduction to MQMAS NMR

AIM: Optimization of the echo or antiecho amplitudes for either the shifted-echo or the split-t1 MQMAS sequences where the first pulse excites a p-quantum coherence only. The powder sample is in a rotor spinning at the magic angle.

MQMAS sequence with pulse lengths p1 and p2

The multi-quantum magic-angle spinning (MQMAS) experiment on half-integer quadrupole spin was introduced by L. Frydman and co-workers. It is an echo experiment involving transitions between non-consecutive energy levels during the excitation of the spin system by the first pulse. The MQ coherences generated by this pulse are converted back to -1Q coherence as an echo and an antiecho by the second pulse. Mainly the central-transition signal is detected.

The echo and the anti-echo amplitudes are a product of two functions: the MQ excitation function A(p1) that depends on p1 and the conversion function B(p2) that depends on p2. The observation of the echo and antiecho requires the optimization of the two pulse-lengths p1 and p2.

The optimization procedure is a two-step experiment, where the delay k*tau1 allows the observation of the whole echo signal (However, the signal acquisition starts at the position tau2 = k*tau1):

In the first experiment, we keep constant p1 and acquire a series of spectra for increasing p2.

In the second experiment, we acquire a series of spectra for increasing p1, where p2 corresponds to that generating the highest spectrum line intensity in the first experiment.

Solid-state NMR bibliography for:

Aluminum-27
Antimony-121/123
Arsenic-75
Barium-135/137
Beryllium-9
Bismuth-209
Boron-11
Bromine-79/81
Calcium-43
Cesium-133
Chlorine-35/37
Chromium-53
Cobalt-59
Copper-63/65
Deuterium-2
Gallium-69/71
Germanium-73
Gold-197
Hafnium-177/179
Indium-113/115
Iodine-127
Iridium-191/193
Krypton-83
Lanthanum-139
Lithium-7
Magnesium-25
Manganese-55
Mercury-201
Molybdenum-95/97
Neon-21
Nickel-61
Niobium-93
Nitrogen-14
Osmium-189
Oxygen-17
Palladium-105
Potassium-39/41
Rhenium-185/187
Rubidium-85/87
Ruthenium-99/101
Scandium-45
Sodium-23
Strontium-87
Sulfur-33
Tantalum-181
Titanium-47/49
Vanadium-51
Xenon-131
Zinc-67
Zirconium-91
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