[Ifeffit] Fitting using Experimental standard

Matthew mamarcus at lbl.gov
Mon Jan 4 21:41:52 CST 2010

An experimental standard is an EXAFS spectrum of a known compound.  If you pick the right known compound (and if such exists) then 
you have an isolatable shell consisting only of scattering from one kind of atom, with
the others being at distances sufficiently different so that one can Fourier-filter them out.  Nowadays, a more standard procedure 
is to fit your standard compound using Artemis or the like, then use that fit as a starting point
for a fit to the unknown.  The accuracy with which the fit to the standard reproduces the known (crystallographic) values tells you 
how well EXAFS worked in the case of your compound.  Also, the coordination number you get
for the dominant shell, relative to what it's "supposed to be", tells you the S0^2.  If you get strange values like 0.1 or 20 then 
you know something's wrong.  If you get plausible numbers, you can think about substituting those in
for the S02 in the unknown and taking the resultant amplitudes as coordination numbers.  Similarly, if the model compound is really 
similar to the unknown, you can start your fit to the unknown using the values for E0 and Ds2 you got from the
----- Original Message ----- 
From: "Fiona R. Kizewski" <jrkizews at ncsu.edu>
To: <bravel at bnl.gov>; "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>
Sent: Monday, January 04, 2010 7:16 PM
Subject: Re: [Ifeffit] Fitting using Experimental standard

> Dear all,
> Can somebody please explain to me what is theoretical standard and what is
> experimental standard. My understanding of theoretical standard is the
> crystallographic data. However, it is first time I heard experimental
> standard.
> Thanks
> Fiona R. Kizewski
> Ph.D. Candidate
> Department of Chemistry
> North Carolina State University
> Raleigh North Carolina 27695
>> On Monday 04 January 2010, 09:15:37 am, abhijeet gaur wrote:
>>> Generally the fitting is done using theoretical standards. For that in
>>> Artemis, we give input as crystallographic data. But If we want to use
>>> an
>>> experimental standard instead of
>>> theoretical standard, how that can be done. Is it possible to use
>>> experimental standard in Artemis? or we have to use some other method.
>> Artemis does not do fitting with experimental standards, although Athena
>> does
>> have a dialog for doing log-ratio/phase-difference analysis.
>> B
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