Fitting First Order Quadrupolar static spectrum...
2D static spectrum of Plexiglass
Quadrupolar tensor definition :
principal values are sorted |Vyy|<=|Vxx|<=|Vzz| note that Vxx and Vyy have
signs opposite to that of Vzz - usually NMR is not sign sensitive for EFG
etaQ is the anisotropy of the Quadrupolar tensor etaQ=Vyy-Vxx/Vzz with
and thus Vxx=1/2 (-EtaQ-1)Vzz and Vyy=1/2 (EtaQ-1)Vzz
Most of the procedure is similar to that described for
Gaussian/Lorentzian lines except for the computing
Model and its parameters...
Step 1 : Setting up the starting solution (the different
Open the file in dmfit [Menu/File/Open] or drag it to dmfit
window from file manager
Initiate a decomposition [Menu/Decomposition/New Fit]
Select a nucleus by Clicking the
button or calling the [Spec Parameters]
dialog. If the nucleus is a quadrupolar nuclei, the list of model will be
extended with to Quadrupolar interaction models.
the [Add] button to add
a new line
Select the "Q-1 stat
the [Drag] button to drag this new line to a
convenient position, Quadrupolar coupling and amplitude,
click left to accept (click right toggles between Amp/Pos and Amp/quadrupolar
Check or modify the lines parameters in the [Fit Pannel] (bottom
the [Compute] button to
recompute the model spectrum
Repeat this procedure for all the lines that you expect.
remark : only the
quadrupolar coupling can be dragged on screen, the asymmetry parameter is
changed by modifying the value in the bottom window.
Line Parameters (Bold parameters are selected for
Amplitude : height of the maximum of the line
Position : Position of the line (in Hertz, ppm or point depending on the current
Em : Apodisation of the theoretical lineshape, this
value is not calibrated in this window, its actual value can be checked in the
Report window. Positive values are Lorentzian apodisation, negative are
Gaussian. To make your mind start with 5 or -5.
nuQ : is the quadrupolar frequency expressed in kHz, the display can also
be set in quadrupolar coupling (CQ) by changing a switch in the
Fit Parameters dialog box
etaQ : is the asymmetry parameter [0..1]
You can always click use the
Fit Paramters Pannel buttons
Step 2 : Optimizing the fit
Check the different lines and their parameters (only
Bold face parameters will be optimized)
If necessary click
the [Parameters] button to call the [Model
Parameters full list] dialog and modify the list of variable paramters
the [Optimize] button to
optimize the current solution
Step 3 : Reporting and Saving
Fit parameters can be saved in machine readable binary
format [Menu/Decomposition/Save Fit] or [Menu/Decomposition/Save as Fit] and
thus retrieved later exactly in same state.
Parameters can be reported in human readable format by clicking
the [Report] button to report the current line
paramters in a dialog box from which you can Select/Copy and further Paste word
processing or SpreadSheet programs.