Re: [Ifeffit] huge S02 value ??

Hello Anatoly, In addition to Ni aqueous solutions, I and my former group members also collected EXAFS of solutions of many Ni-organic complexes which are octahedral (O)in first shell at differet time and on differet beamlines. All the fitting resulted in high S02 values although bond distances are correct and fitting goodness is good as well. My collegue and I also found that a S02 of 0.85 was obtained from the fitting of Ni aqueous solution if we used feff files created from the artificial single Ni-O path instead of from crystal structures using Feff 6. Using files created from Feff 7 with single Ni-O path resulted in a high value close to 1. I am thinking if this high S02 value comes from the Feff code. The versions of Feff that I use is Feff 7.00 and Feff 6. I am wondering if you can send me your EXAFS data of Ni aqueous solution and the Feff you used to creat these files. Thanks for your time and efforts. Best wishes, Mengqiang ----------------------- Mengqiang Zhu Ph.D Candidate Environmental Soil Chemistry Department of Plant and Soil Sciences University of Delaware 152 Townsend Hall Newark, DE 19716 http://ag.udel.edu/soilchem/zhu.html ---- Original message ----

Date: Sun, 5 Apr 2009 21:54:41 -0400 From: ifeffit-bounces@millenia.cars.aps.anl.gov (on behalf of "Frenkel, Anatoly" ) Subject: Re: [Ifeffit] huge S02 value ?? To: "XAFS Analysis using Ifeffit"

Hi, 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.

Anatoly

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From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of mzhu@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 http://ag.udel.edu/soilchem/zhu.html

---- Original message ----

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Date: Sun, 5 Apr 2009 12:44:13 -0400 From: ifeffit-bounces@millenia.cars.aps.anl.gov (on behalf of "Frenkel, Anatoly" ) Subject: Re: [Ifeffit] huge S02 value ?? To: "XAFS Analysis using Ifeffit" ,

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, Anatoly

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From: ifeffit-bounces@millenia.cars.aps.anl.gov on behalf of mzhu@udel.edu Sent: Sat 4/4/2009 10:04 PM To: ifeffit@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 http://ag.udel.edu/soilchem/zhu.html

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