11 - Important remarks
We present the procedure for processing 3QMAS NMR data for aluminum-27 whose nuclear spin I is 5/2. Its gyromagnetic ratio is positive. This procedure is associated with the two-pulse 3QMAS program for I > 3/2.
In fact, this procedure remains unchanged for processing -3QMAS NMR data for a spin I = 3/2 nucleus, such as sodium-23 whose gyromagnetic ratio is also positive, if we use the two-pulse -3QMAS program for I = 3/2.
These two NMR pulse programs differ mainly by the phase cycling of the first pulse during the acquisition of the sine part for the 2D data.
In other words, we need two NMR pulse programs in order to use the same procedure for processing the 2D data.
On the other hand, if we use the same NMR pulse program whatever the nuclear spin I, for example 3QMAS program for I > 3/2, we have to interchange the definitions of echo and anti-echo files for a spin I = 3/2 nucleus, that is,
fecho(t1, t2) = Scos(t1, t2) - i*Ssin(t1, t2)
fanti-echo(t1, t2) = Scos(t1, t2) + i*Ssin(t1, t2)
In other words, we need two processing procedures in order to use the same NMR pulse program.
We will check the above suggestions for nuclei with negative gyromagnetic ratios.