NMR@CEMHTI

Fitting CSA Magic Angle Spinning sideband partterns...

 Example :  31P spectrum fitted with CSA MAS model 3kHz  
 Example :  31P spectrum fitted with CSA MAS model 6kHz  
 Example :  31P spectrum fitted with CSA MAS model 15kHz  
 Example :  13C 200MHz Glycine spectrum 5.033kHz MAS  
 Example :  13C 200MHz Glycine spectrum 1.940kHz MAS  
 Example :  13C 200MHz Glycine spectrum 0.962kHz MAS  
 Example :  MAS spectrum with both QUAD & CSA  

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CSA Parameters :

• principal values are sorted |d33-diso|>|d11-diso|>|d22-diso|
• diso is the isotropic chemical shift 1/3 (d33+d22+d11)
• dCS is the axiality of the CSA tensor (d33-diso)
• etaCS is the anisotropy of the CSA tensor etaCS=(d22-d11)/(d33-diso)

Definitions in agreement with Simpson (Aarhus) M.Bak, J.T.Rasmussen, N.C.Nielsen J. Magn. Reson. 147 296-330 (2000)  

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It is assumed that you know how to fit Gaussian/Lorentzian lines to a spectrum

There exist several possible strategies... the following describes a possible one.

Step 1 : Define the N=0 isotropic lines and the spinning sidebands

1. Locate the N=0 spinning sideband (using other spinning rate, prior knowledge or whatever...)

2. Add a line or Drag an existing one to this position with the [Gauss/Lor] model

3. Add a new line and change its model to [ss band] mode

4. Fill in the two new boxes that appeared in the [Fit Pannel] : spinning sideband number [+/-1, 2..] & reference line number [N=0 band that has just been set]

5. Click the [Drag] button and position the spinning sideband (amplitude and pos), the position & spinning sideband number will update the spinning rate value.

6. Click

7. repeat operation from 3 for all the spinning sidebans that you want to use

8. Save your work, just in case [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save As Fit]

Step 2 : Optimize the parameters

1. Click the [Parameters] button to call the [Model Parameters full list] dialog and add a star at the right of the spinning rate to allow its optimization, quit the dialog box.

2. Click the [Optimize] button to optimize the current solution optimizing Amp/Pos/Width of the ref line, Amp only for the spinning sidebands, and spinning rate.

3. Save your work, just in case [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save As Fit]

Step 3 : Retrieve CSA parameters

You can whether export the table of intensities using the [Report] button and submit this table intensity to other software you rely on

or

estimate the CSA parameters (from precomputed tables) with the dmfit program :

1. Click the [Parameters] button to call the [Model Parameters full list] dialog

2. Select one of the spinning sideband, a button labeled [CSA ??] will appear above

3. Click this button to look the tables for the better match.

4. A dialog box shows up with the better solution taking into account all the spinning sidebands defined

5. If you want you can click the [ssb -> mCSA] button to transform the set of spinning sideband to a single contribution under [CSA mas] model.

6. Quit and recompute the model spectrum.

7. Save your work, just in case [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save As Fit]

8. Remark 1 : Change the spinning rate and recompute to model the spectrum for another spinning rate value if you like to

9. Remark 2 : you can switch from [CSA mas] model to set of spinning sideband by calling the [Model Parameters full list] dialog and clicking the [Explode] button.

Warning : this procedure only provides you with a guess of the CSA parameters, not a real optimized measurement.

Line Parameters (Bold parameters are selected for automatic optimization):
    Amplitude : height of the maximum of the N=0 line
    Position : Isotropic Position of the N=0 line (in Hertz, ppm or point depending on the current unit) positions of the spinning sidebands are given by their numbers, the position of the reference line and the spinning rate.
    Width : full width at half maximum of the line an its spinning sidebands
    xG/(1-x)L : Gaussian/Lorentzian ratio (1 for Gaussian, 0 for Lorentzian) (shared by all the lines of the spinning sidebands maniflod)
    dCS : the axiality of the CSA tensor (in Hertz, ppm or point depending on the current unit)
    etaCS :  the assymetry paramter of the CSA tensor.

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