Re: [Ifeffit] Bkg removal problem

Thx for the detailed answer. Helped me a lot. Also tested it with other programs using smoothed splines, leading to similar results. And you are right, I don't expect a peak at about 1A in the FT. The first peak at 1.5A in the FT should represent a mixed 1st shell of 3O/3N atoms at about 2A distance. best regards Alfred Am 15.09.2010 19:00, schrieb ifeffit-request@millenia.cars.aps.anl.gov:

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Today's Topics:

1. Re: Bkg removal problem (Bruce Ravel)

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Message: 1 Date: Tue, 14 Sep 2010 14:07:55 -0400 From: Bruce Ravel To: XAFS Analysis using Ifeffit Subject: Re: [Ifeffit] Bkg removal problem Message-ID:<201009141407.55193.bravel@bnl.gov> Content-Type: Text/Plain; charset="iso-8859-1"

Alfred,

I certainly encourage you to look at Shelly's book chapter. It's very useful.

The question you ask is one that we hear frequently on this mailing list. I don't mean anything bad by saying that -- in fact, it's an excellent question that every practitioner of XAS needs to come to terms with early on in his or her XAS career. Indeed, I am pleased that you are insightful enough to recognize your confusion and wise enough to ask for help.

That said, I am a bit weary of answering questions about Rbkg on the mailing list. Yours ain't the first! ;-)

Rather than answering here, I decided to write up a wiki page on the topic. That way, I'll have something to point to the next time someone asks about Rbkg.

Here it is: http://xafs.org/TheoryAnalysis/BackgroundRemovalWithAutobk

Hope it helps, B

On Friday 10 September 2010 10:25:50 am Shelly Kelly wrote:

...

Hi Alfred:

You should take a look at my book chapter. I go through a lot of details on how to remove the background. If you want a copy just send me an email directly and I'll send you a pdf.

Cheers, Shelly exafs@netzero.com

On Fri, Sep 10, 2010 at 8:42 AM, Alfred Hummer

wrote:

...

Hello,

Currently I am working on a Ga XAS spectrum. I'm trying to extract the EXAFS data but I'm not sure if the background function is right, or how to set the right values.

I played around with different setting for kmin and Rbkg. So far I know that Rbkg defines the cutoff for the bkg frequencies in the FT optimization and setting it to high leads to loss in information, as more high frequencies are included in the bkg.

I also read that it is advisable to exclude strong white lines from the spline range (increasing kmin?). Would this a strategy in my case?

I attached the project file.

Maybe someone has a clue. The more I tried the bigger my uncertainty.

best regards

Alfred

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