[Ifeffit] E0 on linear combination fitting: fit or not?

[Voegelin, Andreas]

Hi Pamela

I would recommend to set all normalization, background removal and forward Fourier transform  parameters to the same values for all samples and references (not only E0).

Looking at your spectra, it seems to me that your sample spectrum (8MnRh_RED) was measured in fluorescence mode and was affected by self absorption (suggesting that it was too concentrated and/or individual Mn-bearing particles too large).  If you analyze the EXAFS data by LCF, the best fit you can get for your sample spectrum is with 0.62 MnO (if you do not force the LCF sum to unity; based on available references).   You could try to correct the XANES spectrum to eliminate the self-absorption effect.  For the corrected XANES, you would probably also find that the best fit involves only the MnO reference.

Best regards, Andreas


From: Ifeffit [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf Of Carrillo Sanchez, Pamela
Sent: Donnerstag, 11. Mai 2017 19:19
To: ifeffit at millenia.cars.aps.anl.gov
Subject: [Ifeffit] E0 on linear combination fitting: fit or not?



Hi all,

I have gone through the mail archives as well as following the instructions of Athena user's manual as well as Scott Calvin's book but still I find myself with the doubt of how correctly "choose E0". I have aligned the data and standards with the merge of reference foils measurements of the metal (Mn). We did not have a reference foil placed while measuring the data so I used the merge of the references scans when the standards were measured and they showed a consistent energy shift.
 I have set the same E0 for all the data and standard to the same E0, I chose the first peak of the derivative in the data (6MnRh_RED). When I do the LCF analysis without 'fitting E0' ,  I get a worse fitting than when I choose the fit E0 on Athena as well as different types of components on the fitting. Which one is the best choice for it ? From what I have read I think that without fitting E0 would be the proper one regardless of the "worse fit".

Also, I would like to know which fit range would be appropriate for this, I have chosen -20 to +30 eV due to the features of my data and ranges for XANES. Any recommendation.

I have attached the files for the project and screenshots of both fittings.

Any help is highly appreciated!

Pamela

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