[Ifeffit] huge S02 value ??

Frenkel, Anatoly frenkel at bnl.gov
Sun Apr 5 20:54:41 CDT 2009

Very strange. Your data are indeed more intense in k-space than mine, after they are perfectly aligned. Since you have some systematic noise in the end of the k-range, I wonder if you should be better off remeasuring this system, instead of trying to brain storm why it gives high S02.
Of course, it could mean that my data are wrong and your are right. But this is not easy to troubleshoot. If you are in doubt, better to look at other comparisons, between reference materials that you collected during the same run and those that you had measured earlier.


From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of mzhu at udel.edu
Sent: Sun 4/5/2009 1:47 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] huge S02 value ??

Hello Anatoly,
  The E0 I used for EXAFS extraction is 8344 ev, which is located in the half of the edge jump. I tried a higher E0 as you suggested, such as 8347 ev, but I still got a huge S02 value. In the attchment is the mu(E) and average data of Ni solution. I very appreciate your help.

Best wishes,

Mengqiang Zhu

Mengqiang Zhu
Ph.D Candidate
Environmental Soil Chemistry
Department of Plant and Soil Sciences
University of Delaware
152 Townsend Hall
Newark, DE 19716

---- Original message ----
>Date: Sun, 5 Apr 2009 12:44:13 -0400
>From: ifeffit-bounces at millenia.cars.aps.anl.gov (on behalf of "Frenkel, Anatoly" <frenkel at bnl.gov>)
>Subject: Re: [Ifeffit] huge S02 value ?? 
>To: "XAFS Analysis using Ifeffit" <ifeffit at millenia.cars.aps.anl.gov>, <ifeffit at millenia.cars.aps.anl.gov>
>Hi Mengqiang,
>I have done fits of aqueous solution of NiSO4 before and obtained S02 of 0.8 for the octahedrally coordinated Ni-O shell. You did not send the mu(E) data, just chi(k), so I was not able to compare my and your raw data fully, just in k-space. Here is what I found: my data is in perfect agreement in k-space with yours, only if I move E0 down to the pre-edge region, and I suspect, therefore, it is where you chose your E0.
>As a result, the entire, very intense, main absorption peak became a part of your EXAFS, increasing the intensity of the k-space signal (since it became the first half-cycle of the EXAFS oscillation), and thus you got such a large S02. If you move your E0 to half-the edge jump, your result will be the same as mine, 0.8
>Let me know if it helped,
>From: ifeffit-bounces at millenia.cars.aps.anl.gov on behalf of mzhu at udel.edu
>Sent: Sat 4/4/2009 10:04 PM
>To: ifeffit at millenia.cars.aps.anl.gov
>Subject: [Ifeffit] huge S02 value ??
>Hello everyone,
>  I have been fitting EXAFS of NiSO4 aqueous solution. The feff files were created from Ni(OH)2 using Feff7.00. During the fitting, coordination number was fixed as 6. The S02 derived from fitting is 1.22. I tried other materials for creating feff files, such as NiCO3 and NiPO4, and I got the similar S02 values. I also tried Feff6, it did not result in a reasonable S02 value, either.
>   Anyone can tell me why it led to such high S02 value? The data file and feff input file (Feff 7) are attached. 
>   Thanks in advance.
>Best wishes,
>Mengqiang Zhu
>Mengqiang Zhu
>Ph.D Candidate
>Environmental Soil Chemistry
>Department of Plant and Soil Sciences
>University of Delaware
>152 Townsend Hall
>Newark, DE 19716
>Ifeffit mailing list
>Ifeffit at millenia.cars.aps.anl.gov

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