Hello Chris, Bruce, Thank you so very much for your detailed explanations. With best regards, Jatin Rana HZB Berlin On 08.10.2010 19:00, ifeffit-request@millenia.cars.aps.anl.gov wrote:

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Today's Topics:

1. Re: schemes for delr and sigma2 for multiple scattering paths (Chris Patridge) 2. Re: schemes for delr and sigma2 for multiple scattering paths (Bruce Ravel) 3. Re: schemes for delr and sigma2 for multiple scattering paths (Bruce Ravel)

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Message: 1 Date: Fri, 8 Oct 2010 10:09:34 -0400 From: Chris Patridge To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] schemes for delr and sigma2 for multiple scattering paths Message-ID:<68FC92BB-B842-48F2-8596-7675D168EB16@buffalo.edu> Content-Type: text/plain; charset=us-ascii; format=flowed; delsp=yes

Hello Jatin,

I don't confess expertise but i think the absorption coeff. relates to the overlap between the initial and final wavefunction. Therefore the interference between outgoing and backscattering modulates the final wavefunction which manifests as the exafs fluctuations past the edge which in turn changes the It signal so we can use the difference between Io and It to measure exafs data. Any additional comments are welcomed if I am mistaken as I said I am not an expert.

Buena salud,

Chris Patridge

On Oct 8, 2010, at 9:30 AM, Jatinkumar Rana

...

wrote:

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Hi Scott,

Nice to see you back-in-action from holidays. Thank you very much for your suggestions.

Since last few days i was trying to visualize the physical process going on inside an absorbing atom when we measure EXAFS, i met few really basic questions, which of course, could be due to lack of my understandings. Therefore, I tried to go through literatures and EXAFS books but i am not satisfied.

Therefore, i decided to put them to mailing list

My first question is :

In EXAFS, the oscillations are due to the intereference between the outgoing photo electron from absorbing atom and incoming backscattered photoelectron from the scatterer. Depending upon, how much they are out of phase w.r.t each other we get oscillations in EXAFS curve. These oscillations are nothing but the variation in the absobtion coefficient of sample as the energy of incident photon is varied.

I wonder, how, the intereference between the photo electrons is related to absorbtion coefficient of sample ??

because, It = I0 * exp (-ut)

My second question is :

While measuring EXAFS at beamline, we only measure the intial intensity (Io) and the transmitted intenstiy from sample (It). In other words, we only measure the number of photons before and after the sample and variation in abs.coeffi.(u) is related to variation in It.

How interference between photoelectrons will be reflected as variation in abs.coeffi. (u) of sample while we never measure photo electrons in EXAFS??

We only measure Io and It.

Also, whether the intereference between photo electrons is constructive or destructive, the incident photon will lose its energy once it knocks an electron from say K-shell of absorbing atom and hence photon is said to have absorbed.

I will be really thankful to you for your valuable explanation.

With Best regards, Jatin Rana HZB, Berlin

On 07.10.2010 19:00, ifeffit-request@millenia.cars.aps.anl.gov wrote:

...

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Today's Topics:

1. Re: Multiple scattering paths in fitting (Frenkel, Anatoly) 2. Re: schemes for delr and sigma2 for multiple scattering paths (Scott Calvin)

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Message: 1 Date: Thu, 7 Oct 2010 09:38:26 -0400 From: "Frenkel, Anatoly" To: "XAFS Analysis using Ifeffit" Subject: Re: [Ifeffit] Multiple scattering paths in fitting Message-ID: Content-Type: text/plain; charset="iso-8859-1"

For relationships between sigma2 for MS and SS paths, some are listed in the Appendix to this article:

P. Shanthakumar, et al, Physical Review B 74, 174103 (2006).

Anatoly