[Ifeffit] Aligning EXAFS E0 to Theory

Carter Abney abneycw at uchicago.edu
Wed Jun 4 15:18:37 CDT 2014

Hello, Everyone -

This is my first time trying to work through EXAFS analysis of experimental data, and I've got what (I think) should be a fairly straightforward question.  I'm trying to minimize my delta E0 by aligning the EXAFS data with my best fit (i.e. - align the k-grid of the data with the k-grid of the theory to obtain a small delta E0).  However, I have been unsuccessful in "reading the theoretical chi(k) spectrum into Athena<http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg02494.html>" to accomplish this.

I assume the crux of the problem is the format in which I am exporting my theoretical chi(k) spectrum from Artemis.  The only way I have been able to export the data with Artemis so Athena can import it is to click the "Save next plot to a file" button, which then allows me to save the data as a text file.  I know I need chi(k) data that is not k-weighted<http://www.mail-archive.com/ifeffit%40millenia.cars.aps.anl.gov/msg01623.html>, so I plot the best fit with k-weight of 0 in k space with deltaE0 equal to 0.  Considering the problems I've had, I'm assuming somewhere in this process is where I'm going wrong.

When I import this data, I have four columns: k, experimental data, fit, window.  Since k is the wavenumber of the photoelectron, I choose that as "Energy."  Then I select column 3, the best fit, as "Numerator," and change the data type to chi(k).  I then import the data.  I've attached two pngs to this e-mail which, assuming they come through, should display the Athena data import window and the corresponding plot of chi(k).  When I plot this data in k-space or R-space using Artemis, the resulting plots look appropriate.

When I try to align the experimental EXAFS data in Athena, I know it aligns the first derivative of E for the selected data to the first derivative of E for the standard.  I want my best fit to be the standard to which the data is aligned.  However, I cannot plot chi(k) data in E, which causes me to believe I shouldn't be able to align data to the first derivative of E.  True enough, when I try to auto align, I get impossible values for E0 adjustment.

Clearly I'm doing something wrong - possibly even several somethings wrong.  Any guidance would be greatly appreciated.


- Carter

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