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
model.
mam
----- Original Message -----
From: "Fiona R. Kizewski" <jrkiz...@ncsu.edu>
To: <bra...@bnl.gov>; "XAFS Analysis using Ifeffit"
<ifeffit@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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