[Ifeffit] New Method for Normalization?

[Barton, David (DG)]

Bruce,

You mentioned:
> Isn't Ifeffit's Cromer-Liberman normalization scheme 
> substantially similar to the method presented in that paper?
> 

When I use the Cromer-Liberman background subtraction routine in Athena the Normalized data is not flattened.  Normalized, but not *flattened* data results in a skewed XANES region which is affected by the amount of curvature in the background.  If I choose "Flatten" in Athena, it is my understanding that it applies a linear pre-edge and 2nd order polynomial post-edge regardless of which background was chosen (Autobk or CLNorm).  The Clnorm background does appear to "flatten" the chi(k) data which can be useful for EXAFS analysis, but it doesn't flatten the mu(E) data.  When one attempts to analyze XANES data it is preferred to have the entire post-edge "flattened" in mu(E) space so that the background curvature is eliminated from the dataset.

Ultimately, as Matt stated, it would be nice to be able to combine a Victoreen and CLNorm background to get a reasonably "flattened" mu(E) function.  I would also suggest adding the ability to independently set the pre-edge and post-edge functions (n'th order polynomial, Victoreen, CLNorm, or MBACK??) for Normalization and Flattening.  These choices would be separate from the choice of background removal method to get chi(k) (Autobk or CLNorm). 

Dave

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> Of Bruce Ravel
> Sent: Thursday, September 29, 2005 5:20 PM
> To: XAFS Analysis using Ifeffit
> Subject: Re: [Ifeffit] New Method for Normalization?
> 
> 
> On Thursday 29 September 2005 15:48, Barton, David (DG) wrote:
> > Has anyone considered using the methods of Penner-Hahn to normalize 
> > their data to get reliable intensities of near-edge features?  The 
> > reference to their method of normalization is below:
> >
> > J. Synchrotron Rad. (2005). 12, 506-510    
> [doi:10.1107/S0909049504034193]
> > "A method for normalization of X-ray absorption spectra" 
> T.-C. Weng, 
> > G. S. Waldo and J. E. Penner-Hahn
> >
> > It is my understanding the Ifeffit uses a linear function to remove 
> > the pre-edge and a quadratic for the post-edge and that the 
> Athena's 
> > flatten is a subtraction of these functions.  This is an excellent 
> > method under most scenarios since the background is usually fairly 
> > smooth and can be well approximated by a quadratic equation.  
> > Personally, I have had only a few rare cases where the quadratic 
> > function on the post-edge was not sufficient to reliably 
> normalize the 
> > data and in those cases a third-order polynomial was 
> sufficient.  Does 
> > anyone else have an opinion on using alternative normalization 
> > routines?
> 
> Isn't Ifeffit's Cromer-Liberman normalization scheme 
> substantially similar to the method presented in that paper?
> 
> B
> 
> 
> -- 
>  Bruce Ravel  ---------------------------------------------- 
> bravel at anl.gov
> 
>  Molecular Environmental Science Group, Building 203, Room 
> E-165  MRCAT, Sector 10, Advance Photon Source, Building 433, 
> Room B007
> 
>  Argonne National Laboratory         phone and voice mail: 
> (1) 630 252 5033
>  Argonne IL 60439, USA                                fax: 
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> 
>  My homepage:    http://cars9.uchicago.edu/~ravel 
>  EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/
> 
> 
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