[Ifeffit] distinguishing between actual shells and artifacts

[Kelly, Shelly]

Hi Hashem,

I show one method for doing this in my book chapter Figure 14-23 on page 431. (I feel a bit like a broken record).  I will send you a copy if you want.

Shelly

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-
> bounces at millenia.cars.aps.anl.gov] On Behalf Of Voegelin Andreas
> Sent: Wednesday, January 14, 2009 9:57 AM
> To: XAFS Analysis using Ifeffit
> Subject: Re: [Ifeffit] distinguishing between actual shells and artifacts
> 
> Hi Hashem
> 
> You can copy-paste the respective EXAFS data in Athena and compare the
> backtransforms over the first shell, the first+second shell, the second
> shell.
> 
> By comparison of the backtransforms with each other and with the measured
> EXAFS, you can see where the second-shell contribution has its origin in
> k-space (note that the backtransform is not corrected for the window
> function).
> 
> For instance, if the second-shell signal adds to the spectrum in the low-k
> range (where noise should not be a problem), it is likely real and might
> result, e.g., from multiple scattering among first-shell O atoms. If the
> second-shell signal in the backtransform mainly contributes in the high-k
> range (where noise or glitches may be a problem), you may be able to see
> whether it falls together with obvious artefacts (such as glitches), or
> whether the backtransform matches spectral features that you consider to
> be real.
> 
> Andreas
> 
> -----------------------------------------------
> Andreas Voegelin, PhD
> Soil Chemistry Group
> Inst. of Biogeochemistry and Pollutant Dynamics
> Dept. of Environmental Sciences
> ETH Zurich
> Universitätstrasse 16, CHN F24
> CH-8092 Zürich, Switzerland
> Phone: +41 44 633 61 47
> Fax: +41 44 633 11 18
> E-Mail: voegelin at env.ethz.ch
> www: http://www.ibp.ethz.ch/people/andreavo
> 
> 
> 
> > -----Original Message-----
> > From: ifeffit-bounces at millenia.cars.aps.anl.gov
> > [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf
> > Of mstiet2 at lsu.edu
> > Sent: Mittwoch, 14. Januar 2009 14:12
> > To: ifeffit at millenia.cars.aps.anl.gov
> > Subject: [Ifeffit] distinguishing between actual shells and artifacts
> >
> > Dear all,
> >
> > I am currently fitting first and second shells with Zn-O and
> > Zn-Zn paths,respectively. I get second shell features that
> > could be fit quite well, but I am not certain if they are
> > actually second shell features or possibly artifacts. For
> > some samples I get second shell features that I know should
> > not be present. What criteria would you use to distinguish
> > between artifacts and actual shells?
> >
> > Your assistance is appreciated.
> >
> > Hashem Stietiya
> >
> > Louisiana State University
> >
> >
> >
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit