[Ifeffit] Fitting pre-edge feature in Fe XANES

[Erik Farquhar]

Hi Sharon,

In addition to Bruce's excellent advice on treating pre-edge analysis as a
generic fitting problem, you may also want to have a look at an earlier
systematic survey of Fe pre-edge analysis:  Westre, et al., J. Am. Chem. 
Soc. 1997, 119, 6297-6314 DOI: 10.1021/ja964352a. Note the constrained 
fitting range in that paper, which simplified the fitting problem a bit since they 
did not need to worry about accurately fitting the edge step and bumps 
along the rising edge using step functions and the like.

The only useful application of EXAFSPAK to your problem would be
to fit the pre-edge data using the EDG_FIT program of that package (this
was used in the Westre paper referred to above). This program has 
something of a learning curve to use well. If you have another peak-
fitting program that you like, then it's best to stick with that one.

Good luck,
Erik

--
Erik Farquhar, Ph.D.
Case Center for
Synchrotron Biosciences
Brookhaven National
Lab
NSLS, Building
725A-X3
Upton, NY 
11973
efarquhar at bnl.gov
+1-631-344-8174


________________________________
From: "shbone at berkeley.edu" <shbone at berkeley.edu>
To: ifeffit at millenia.cars.aps.anl.gov 
Sent: Friday, June 8, 2012 2:18 PM
Subject: [Ifeffit] Fitting pre-edge feature in Fe XANES

Dear All:

I would like to attempt fits to the pre-edge features of a set of Fe
K-edge XANES spectra for Fe(II) samples that show partial oxidation with
the goal of determining whether Fe(III) exists in octahedral or
tetrahedral coordination (e.g. Wilke et al., American Mineralogist, 2001).

Broadly, the fitting procedure involves extracting the pre-edge feature
from the edge using a spline function and then deconvoluting this feature
using a set of pseudo-voigt functions.

I believe that I can use the LCF module in Sixpack to fit the feature
using the pseudo-voigt functions, but I'm having trouble extracting the
pre-edge feature.

I've tried using the spline function in Sixpack (and Athena), but I don't
have enough options to modify the spline. It seems to me that I need to
use a very rigid spline (for instance, one with only 3 or so knots), and
that the options in Sixpack and Athena don't allow for this.

I heard the program exafspak would allow me more freedom to control the
spline function, but I haven't been able to successfully download the
program, let alone use it. So, my questions are the following:

(1) Is there a program other than exafspak that I could use to fit a
spline to my data where I would have more control over the spline options?
I would prefer not to use exafspak since my knowledge of unix is nil.

(2) Has anyone used exafspak on a mac? I'm using OS 10.5.8 and I'd
appreciate any tips you might be able to give me on installing the
program. I followed the directions for installation provided on the
website, but the command to install the program (i.e. "add_exafs") wasn't
recognized.

Thanks for your help!

Sharon




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