[Ifeffit] Trouble with fitting with Arthemis

Kleper Oliveira Rocha k.o.rocha at gmail.com
Tue Jan 13 20:02:27 CST 2009

Hi Carlo,

You seem to be right. I try to do the fit in my notebook, which has the same
Windows and Services Packs, and worked. I want to know why? Is it possible
to resolve this?
You right too assuming that there is an H2 adsorbed. In reality, this is a
sample catalyst of 1%Pt supported in Al2O3 that was treated in H2. The data
of EXAFS was colleted at 500ºC in an flux of H2. It is a catalysts prepared
by impregnation method. In the fit model I assuming that is possible to has
a oxigen neighbor to Pt, therefore, there is a PtO2 model atom to do the
fit. They work well with one path unless by the peak at 1A. I already
thought to assuming a H atom neighbor to Pt but, I not find a good model to
this. Do you have some idea if is possible to do that? Do you belives that I
should take more than one path for Pt-Pt distance?

2009/1/13 Carlo Segre <segre at iit.edu>

> Hi Kleper:
> There is a single Pt-Pt path in your fit.  This is effectively a fcc Pt
> distance of 2.77.  I see several problems:
> This spectrum has distances which are much shorter than 2.77 and so I
> would expect that this single path would not be a very good fit.  I am not
> sure if the peak around 1.1A is real, but it could be given the hydrogen
> that you indicate is present in the file name.  What is clear is that the
> bigger peaks are not Pt-Pt peaks at all.  The Pt-Pt peak will usually
> appear around 2.5A in Chi(R).
> The second thing that I noticed, is that you must have a problem with your
> installation of the software because I just took your file and executed
> the fit and did not get the strange values for Chi^2 and reduced Chi^2
> that you have posted.  The value for amp is negative, indicating that the
> path is not a good model, but the Chi^2 I got was around 1000.
> I can't tell much form the name of your file but I suspect that you have
> Pt-Al and possibly Pt-H distances in your sample.  Do you have any other
> information about this sample?
> Carlo
> --
> Carlo U. Segre -- Professor of Physics
> Associate Dean for Special Projects, Graduate College
> Illinois Institute of Technology
> Voice: 312.567.3498            Fax: 312.567.3494
> segre at iit.edu   http://www.iit.edu/~segre   segre at debian.org
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Kleper de Oliveira Rocha
Doutorando em Engenharia Química
Departamento de Engenharia Química/UFSCar
Tels. 55 016 3351-8694
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