Re: [Ifeffit] Ifeffit Digest, Vol 91, Issue 30

Thanks Matt, now I realize that I can directly change de Eo in the Athena window, Elsa At 14:00 30/09/2010, you wrote:

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1. Re: Ifeffit Digest, Vol 91, Issue 28 (Matt Newville)

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Message: 1 Date: Thu, 30 Sep 2010 11:28:28 -0500 From: Matt Newville To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Ifeffit Digest, Vol 91, Issue 28 Message-ID: Content-Type: text/plain; charset=ISO-8859-1

Hi Elsa,

On Thu, Sep 30, 2010 at 10:33 AM, Elsa Sileo wrote:

...

Dear Matt,

I have to perform EXAFS analysis, and when I tried to fit the first shell, I found deltaE0 values of about 8 eV. Following the paper of Kelly et al (Analysis of soils and minerals using X-ray absorption spectroscopy. In Methods of soil analysis, Part 5: Mineralogical methods; 2008; pp 446) I fitted the first shell obtaining values for deltaE0, sigma^2; delta R and amplitude. Then, using the obtained values, and making deltaE0=0, I got the theoretical signal.

Why is important to have a theoretical spectra with deltaE0=0?

...

When I compare the experimental and theoretical spectrum I see a mismatch between the position of the nodes at low wavenumbers.

Yes, that is what E0 does.

...

Having done this, how I have to proceed to correct the experimental data in order to obtain smalller delta E0 values?

I think what you are trying to do (though I don't understand why) is to adjust E0 for the experimental data so that the fit to a particular theoretical standard gives deltaE0 close to zero. If so, you want to adjust E0 in the background subtraction. If you change E0 by 8eV there, you should end up with a deltaE0 in the fit that is close to zero.

Hope that helps,

--Matt

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Dra. Elsa E. Sileo Solidos Inorganicos INQUIMAE - Dto. Qca. Inorganica, Analitica y Qca. Fisica; FCEN, UBA Int. Güiraldes 2160, Pabellón 2, Piso 3, Ciudad Universitaria - C1428EHA CABA - Argentina Tel: (54 11) 4576 3380 ext. 113 Fax: (54 11) 4576 3341 e-mail: sileo@qi.fcen.uba.ar