[Ifeffit] Very large exafs amplitude in collected data - cause unknown

Bruce Ravel bravel at bnl.gov
Tue Jun 4 09:00:39 CDT 2013

On 06/04/2013 12:25 AM, Jason F. Alvino wrote:
> Hi,
> We have collected fluorescence data of PPh3 protected Au nanoparticles
> supported on an anatase surface at the Au L3 edge, which provides some
> decent looking exafs and seems to fit a bulk gold model rather well (there
> seems to be agglomeration on the surface, even with our low loadings).
> We have tried to fit the data using both XFIT and EXAFSPAK, but the strange
> thing is that the exafs oscillations have a huge amplitude, up to 80 in
> some cases.  Because of this, the only way to fit the data while
> maintaining sensible Debye-Waller factors is to allow SO2 to become quite
> large, or to allow the coordination numbers to become very large.
> We have spoken to a few others in the field and they have yet to be able to
> rationalize why there is such a large signal.
> I have attached an example of one of the data sets with very large
> amplitude, if anyone would be willing to take a look at the data it would
> be much appreciated.


I think it's interesting that a user of two different software packages 
that do not rely upon Ifeffit turns to the Ifeffit mailing list for 
help.  That's great!  This list obviously fills an important gap.

There are rather a lot of columns (189!) in each of your data files and 
the header is not very clear about what's what.  You might consider 
reducing those large, unwieldy, complex, poorly documented files into a 
more easily digested form.  I have no clue how to turn the contents of 
those files into plottable data.  Given that you are asking someone to 
volunteer their time to help you solve a problem, it seems unkind to 
make it so very difficult for a willing volunteer to understand the 
nature of your problem.


  Bruce Ravel  ------------------------------------ bravel at bnl.gov

  National Institute of Standards and Technology
  Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2
  Building 535A
  Upton NY, 11973

  Homepage:    http://xafs.org/BruceRavel
  Software:    https://github.com/bruceravel

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