Re: [Ifeffit] X AS tutorial videos
Hi
Diamond is happy for anyone to download them. I find the program vlc works well for them.
We put them on our anonymous ftp site, but occasionally they are cleared
The current link is:
ftp://ftpanon.diamond.ac.uk/XAS2011/
Thanks
Fred
Sent from Samsung tablet
-------- Original message --------
From: ifeffit-request@millenia.cars.aps.anl.gov
Date:14/10/2015 16:38 (GMT+00:00)
To: ifeffit@millenia.cars.aps.anl.gov
Subject: Ifeffit Digest, Vol 152, Issue 11
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Message: 1
Date: Wed, 14 Oct 2015 10:41:06 -0400
From: Bruce Ravel
Dear all experts, I am processing two As K edge EXAFS data shown as following figure. The first shell is As-O. The difference of the As-O peak btween sample As1 and As2 is around 0.03A. Does this represent that the average As-O bond length of sample As1 should be around 0.03 A longer than that of sample As2? Or this depends on fitting results ? Any help is very appreciated. Cheers, Shaofeng -------------------------------------- Shaofeng Wang, Ph.D of Geochemistry Environmental Molecular Science Group Institute of Applied Ecology, Chinese Academy of Sciences Shenyang, 110016, China wangshaofeng@iae.ac.cn www.iae.cas.cn
Dear Shaofeng,
You really do need to fit to know for sure. Aside from changes in bond length, there are many other effects that can shift a peak.
—Scott Calvin
Sarah Lawrence College
On Nov 4, 2015, at 7:29 AM, Shaofeng Wang
Shaofeng,
On Wed, Nov 4, 2015 at 6:29 AM, Shaofeng Wang
Dear all experts,
I am processing two As K edge EXAFS data shown as following figure. The first shell is As-O. The difference of the As-O peak btween sample As1 and As2 is around 0.03A. Does this represent that the average As-O bond length of sample As1 should be around 0.03 A longer than that of sample As2? Or this depends on fitting results ?
If some assumptions hold, it probably is a good indication that the bond length is probably a bit longer. The main assumptions would be a) that you know the As is surrounded by only oxygen, and b) that the data k-range, Fourier transform parameters, and value for E0 are exactly the same for the two data sets. Even with those assurances, the position of maximum of |chi(R)| is difficult to determine with high accuracy. In fact, for almost all work with Artemis, the grid spacing for the chi(R) data is ~0.0307 Ang (pi/10.24), which is suspiciously close to your observed difference. As an alternative, to looking at the position of the maximum of |chi(R)|, it might be more precise to use the position where the imaginary part of chi(R) crosses zero. This should be the same position, but allows you to use linear interpolation to find the location of that zero. A full fitting of the As-O shell has the ability to be more accurate and use all data, not just one position of chi(R). Still, such differences in where Im[chi(R)]=0 can be a useful guide for further analysis. Cheers, --Matt
Any help is very appreciated.
[image: image]
Cheers,
Shaofeng -------------------------------------- Shaofeng Wang, Ph.D of Geochemistry Environmental Molecular Science Group Institute of Applied Ecology, Chinese Academy of Sciences Shenyang, 110016, China wangshaofeng@iae.ac.cn www.iae.cas.cn
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participants (4)
-
fred.mosselmans＠diamond.ac.uk -
Matt Newville -
Scott Calvin -
Shaofeng Wang