Since S02 is a parameter in the description of EXAFS and not of the
experiment, it's independent of technique. Overabsorption (misnamed
'self-absorption') can reduce the *measured* amplitude, an effect which
can be fudged in analysis by reducing S02. If the sample is truly
homogeneous (on the scale of the absorption length), then you can
calculate the amount of overabsorption to see if it's significant.
However, many kinds of samples, such as concentrated powders mixed with
a diluent such as BN, this condition is not met. If the particles are
large enough for each to have significant absorption edge jumps, then
diluting them in BN doesn't fix the problem.
mam
On 10/2/2021 12:49 AM, Peng Liu wrote:
Dear IFEFFIT members,
I am sorry to bother you again. I asked about S02 selection for the
first major revision. I just received the second revision. The reviewer
is not satisfied with one S02 value for all our samples.
"
1. I am still not satisfied with selected SO2 value (it is set to 0.85).
SO2 is not transferable between different samples and detection methods.
It is not possible to use a value obtained from different compound using
transmission measurement mode to completely different other compound
measured using fluorescence mode. One method to fix SO2 value is to
measure diluted solution (to avoid self-absorption) of reference
material in fluorescence mode. Other is to use multiple spectra fitting
for all samples of interest (e.g. with Sb(V)) measured using
fluorescence mode where SO2 parameter is the same for all samples.
At the same time I am confident that CN values 5.6, 7.1 and 6.9
correspond to CN(Sb-O)=6. I suggest reconsidering the SO2 value for
measurements in fluorescence mode.
"
We do get the S02 from a similar reference material measured in
transmission mode, and our samples were all measured in fluorescence
mode. It is not possible to measure the diluted reference material in
fluorescence mode in one or two months. If you could give me some
suggestions, that would be great.
--
Best Regards,
Peng Liu
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