[Ifeffit] S02 selection from reviewer

[John J Rehr]

Hi everyone

I wonder how much effect on the expt value of S02 comes from background
subtraction including previous edges, the energy dependence of the atomic
background, and the range of the EXAFS. Theoretically S02 is nut a constant
but a spectral average. I’d like to see a careful study with a well defined
algorithm that could be compared with theoretical estimates. Thanks.

John

On Sat, Oct 2, 2021 at 8:47 AM Anatoly Frenkel <
anatoly.frenkel at stonybrook.edu> wrote:

> I think that the variability of S02 between different samples, detection
> methods etc. may or may not be a big concern for you if 1) the error bars
> in the CNs (that you are not reporting) are larger than the difference in
> their mean values (that you are reporting), and/or 2) larger than the
> difference between their mean values and the CN=6 that the reviewer is
> asking about. If yes to either 1) or 2), then the variability in the S02
> values for differently prepared samples may cause smaller variation in your
> best fit values of CN than the error bars reported by your fitting program,
> and your choice of fixing your S02 to be constant (0.85) may be justified.
> You need to have a really bad non-uniformity or concentration problem so
> that your effective S02 changed from the expected 0.85 (assuming it is what
> a correctly performed measurement would give) to, say, 0.5 or 0.6 is my
> thought.
>
>
> Anatoly
>
>
>
> On Sat, Oct 2, 2021 at 3:50 AM Peng Liu <liupeng5182 at gmail.com> 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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