• Import data file
• Acquisition
  parameters
• Separate
  interleaved data
• Echo file
• Anti-echo file
• F2 Fourier
  transform
• Shearing
  2D map
• F1 Fourier
  transform
• Pure absorption 2D lineshape
• F1 and F2 offsets
• Important remarks

5 - Anti-echo file

For aluminum-27 (I = 5/2), which has a positive gyromagnetic ratio, and for 3QMAS experiment performed with the two-pulse program, the antiecho f^anti-echo(t₁, t₂) signal is related to the cosine S^cos(t₁, t₂) and sine S^sin(t₁, t₂) signals by:

f^anti-echo(t₁, t₂) = S^cos(t₁, t₂) - i*S^sin(t₁, t₂)   .

To get -i*S^sin(t₁, t₂) from i*S^sin(t₁, t₂) obtained previously for the echo signal, we apply a phase shift of 180° to i*S^sin(t₁, t₂).

(1) To this end, we recall the sin files by selecting the menu items:

Data/sin

(2) We perform twice a 90°-phase correction, that is, we select twice the menu items:

Process/Phase/Phase Correct

We obtain exp(i*Pi/2)*exp(i*Pi/2)*i*S^sin(t₁, t₂), that is, -i*S^sin(t₁, t₂).

Figure 1 Intensity plot of the -i-phase corrected sine file of 2D MQMAS data:
Both axes of the 2D map are labeled in time units.

(3) We add the S^cos(t₁, t₂) file with -i*S^sin(t₁, t₂) file to build the anti-echo file f^anti-echo(t₁, t₂) by selecting the menu items:

Data/Add Data...

A window appears, in which we add sin to cos. (The two shadowed rectangles are in fact pop-up lists of filenames, clicking on them allows us to choose files.) We save the resulting file with antiecho filename.

Three 2D files corresponding to the 2D anti-echo MQMAS data appear on the desktop:

• antiecho -> 2D Data - Stacked Plot
• antiecho -> 2D Data - Line Contour Plot
• antiecho -> 2D Data - Intensity Plot

Figure 2 Intensity plot of the 2D anti-echo MQMAS data:
Both axes of the 2D map are labeled in time units.