[Ifeffit] Using the amplitude reduction factor as a linear combination fitting parameter

Bruggeman Christophe cbruggem at sckcen.be
Tue Apr 29 02:06:28 CDT 2008

I have recently collected EXAFS spectra of uranium on a FeS2 surface.
Using principal component analysis of the XANES and k3-weighted EXAFS
spectra, I have found that there are two uranium species which compose
the spectra. As a first tentative guess, I believe these two uranium
species are uraninite (UO2(c)) and a uranyl species. I would like now to
fit the fourier transform functions (real parts and magnitudes) using
the theoretical paths and path degeneracies created by feff, and use the
amplitude reduction factor S02 as a fitting parameter to derive the
relative amounts of the two uranium species in my samples. 
Normally, this S02 is taken as a constant (between 0.7 and 1.0), and the
path degeneracies are fitted. So normally, S02 is not really a fitting
parameter (some papers derive it even with theoretical functions).
However, given the fact that S02 and N are completely correlated, I
think it is justified to use this approach. 
Can someone comment on this?
Many thanks in advance,

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