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Today's Topics:

1. Re: Vanadium pre edge peak contributes to K-space? (Bruce Ravel) 2. Re: Vanadium pre edge peak contributes to K-space? (Chris Patridge)

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Message: 1 Date: Tue, 25 Aug 2009 11:32:41 -0400 From: Bruce Ravel Subject: Re: [Ifeffit] Vanadium pre edge peak contributes to K-space? To: XAFS Analysis using Ifeffit Message-ID: <200908251132.41271.bravel@bnl.gov> Content-Type: text/plain; charset="iso-8859-1"

On Tuesday 25 August 2009 11:02:26 am Chris Patridge wrote:

...

Hello all,

After calibration, alignment and merging V K edge data, there seems to be a large peak in R space below 1 A. From most examples and readings, this would seem to be noise since atoms do not reside that close to each other. Adding a background addresses this noise but then the number of variables becomes too large and meaningless to the first shell R space range. I believe the problem lies with the large pre edge feature seen with high valence state Vanadium compounds. Any suggestions on how to work through this and make realistic EXAFS analysis on these compounds.

Thanks everyone,

Didn't Richard Mayes answer this same question from you last month?

http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2009-July/004365.html

In my experience, Richard's answer was spot on for V K edge data.

If Richard's good advice didn't help, then you need to be more explicit about what the problem is, perhaps by posting a small athena project file that demonstrates the problem.

B

--

Bruce Ravel ------------------------------------ bravel@bnl.gov

National Institute of Standards and Technology Synchrotron Methods Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973

My homepage: http://xafs.org/BruceRavel EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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Message: 2 Date: Tue, 25 Aug 2009 11:44:38 -0400 From: Chris Patridge Subject: Re: [Ifeffit] Vanadium pre edge peak contributes to K-space? To: XAFS Analysis using Ifeffit Message-ID: <4A9406E6.9070808@buffalo.edu> Content-Type: text/plain; charset="iso-8859-1"

Bruce Ravel wrote:

...

On Tuesday 25 August 2009 11:02:26 am Chris Patridge wrote:

...

Hello all,

After calibration, alignment and merging V K edge data, there seems to be a large peak in R space below 1 A. From most examples and readings, this would seem to be noise since atoms do not reside that close to each other. Adding a background addresses this noise but then the number of variables becomes too large and meaningless to the first shell R space range. I believe the problem lies with the large pre edge feature seen with high valence state Vanadium compounds. Any suggestions on how to work through this and make realistic EXAFS analysis on these compounds.

Thanks everyone,

Didn't Richard Mayes answer this same question from you last month?

http://millenia.cars.aps.anl.gov/pipermail/ifeffit/2009-July/004365.html

In my experience, Richard's answer was spot on for V K edge data.

If Richard's good advice didn't help, then you need to be more explicit about what the problem is, perhaps by posting a small athena project file that demonstrates the problem.

B

Yes it is a very similar question. I did make this type of correction by setting E0 myself. When moving to R space the data shows significant intensity below 1 A which I thought was noise but it may not be. Are these low A signals data or noise is my main concern because EXAFS fitting does not fit all that well which then would point me to my model as the problem which I think i understand.

Thank you all for your patience,

-- Christopher J. Patridge Graduate Student SUNY Buffalo - Dept of Chemistry 716-645-6800 x 2110 315-529-0501