[Ifeffit] Comparing similar peak positions in Fourier transform with fitting results

[Hashem Stietiya]

Greetings to all,

I am working on Zn binding to Fe and Al oxides and I am trying to fit the
second and third shells. I have three spectra from three samples that differ
in a particular treatment. Visually speaking, the Fourier transforms for
all these spectra show second and third shells at 2.6 and 3.2A (uncorrected
for phase shift), respectively. I fit the second shell with Fe and the third
shell with Al. From the fitting results I obtained the Zn-Fe and Zn-Al
radial distances for the second and third shells. However, these Zn-Fe and
Zn-Al radial distances were different among the samples. For example, the
Zn-Fe radial distance was 3.18A for sample 1, 3.44A for sample 2 and 3.51A
for sample 3. My question is: if the peaks in the Fourier transforms are at
the same position for all samples, why is it that the fitting shows that the
radial distances are actually different? NOTE: I fit the 1st,2nd and 3rd
shells(R range:1.0-3.2A) together.
 Thank you,
Hashem Stietiya
School of Plant, Soil and Environmental Sciences
Louisiana State University
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