Aimee,
It is possible, but probably not advisable to set the E-Eo before linear
combination fitting. If you set Eo before fitting using the
Eo that Athena reports (or any other method of estimating Eo) for each
dataset you will probably be subtracting a different Eo from each XANES
dataset. Then when you do the linear combination fitting each of the
data sets are not on the same x-axis. Thanks to Bruce, he put in the
ability to Fit Eo in the Linear combination fitting window which may
correct for these differences that you imposed on your datasets, but why
add complexity to your fitting. With that said if you picked a single
Eo (say for the metal foil) and subtracted it from each dataset this
would avoid the issue that I just described, however now you must be
sure that each spectrum that you are using is calibrated because you
have lost the ability to use the Calibration feature that Athena has
built in by setting the "E Shift" to the same -Eo value for each
dataset.
This is why it would be advisable to set E-Eo after you have completed
your linear combination fitting using the nice workaround that Andreas
provided.
Dave
________________________________
From: ifeffit-bounces@millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On Behalf Of Aimee
Morey
Sent: Thursday, March 12, 2009 3:07 PM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] XANES
David, Scott and Andreas,
Thanks you so much, that is exactly what I want to do. Another
question before I get myself into trouble. Is it advisable to set E-Eo
before or after I want to analyze with linear combinations? Or is
either option viable?
Aimee
On Thu, Mar 12, 2009 at 12:55 PM, Voegelin, Andreas
wrote:
Hi
Assuming your spectrum is calibrated and you know the
"correct" E0 , you can use the following workaround to plot data on a
(E-E0) axis: set the energy shift in Athena to "minus E0" and Athena's
E0 to zero.
Andreas
________________________________
Von: ifeffit-bounces@millenia.cars.aps.anl.gov im
Auftrag von Barton, David (DG)
Gesendet: Do 12.03.2009 17:31
An: XAFS Analysis using Ifeffit
Betreff: Re: [Ifeffit] XANES
Bruce,
I believe what Aimee wants to see is E-Eo (eV) plotted
on the x-axis
instead of E (eV) in the Athena plot window. I don't
think you have the
option anywhere in Athena to plot the data like this.
Aimee,
Athena does let you easily export the data as an x-y
dataset that can
you put into your favorite plotting software and do the
simple
subtraction that you desire to plot.
Dave
-----Original Message-----
From: ifeffit-bounces@millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces@millenia.cars.aps.anl.gov] On
Behalf Of Bruce
Ravel
Sent: Thursday, March 12, 2009 9:11 AM
To: XAFS Analysis using Ifeffit
Subject: Re: [Ifeffit] XANES
On Thursday 12 March 2009 08:24:44 am Aimee Morey wrote:
> I have collected full XANES and EXAFS spectra. I have
imported the
full
> spectrum into Athena. I am now trying to analyze
using XANES, but I
am
> have trouble figuring out how to set an absolute
energy, i.e. 7709 eV
= 0
> eV or such, and have the energy scaled negatively and
positively. It
is
> probably super simple, can anyone please help?
Hi Aimee,
Data calibration is explained in the Athena User's
Guide:
http://cars9.uchicago.edu/~ravel/software/doc/Athena/html/process/cal.ht
ml
<http://cars9.uchicago.edu/%7Eravel/software/doc/Athena/html/process/cal
.ht%0Aml>
If that is too terse or does not address your question,
you might
consider making a small Athena project file which
demonstrates what
you are confused about and then post that to the mailing
list.
Posting data is usually the best way to get a concrete
answer.
B
--
Bruce Ravel ------------------------------------
bravel@bnl.gov
National Institute of Standards and Technology
Synchrotron Methods Group at NSLS --- Beamlines U7A,
X24A, X23A2
Building 535A
Upton NY, 11973
My homepage: http://xafs.org/BruceRavel
EXAFS software:
http://cars9.uchicago.edu/~ravel/software/exafs/
http://cars9.uchicago.edu/%7Eravel/software/exafs/
_______________________________________________
Ifeffit mailing list
Ifeffit@millenia.cars.aps.anl.gov
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
_______________________________________________
Ifeffit mailing list
Ifeffit@millenia.cars.aps.anl.gov
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
_______________________________________________
Ifeffit mailing list
Ifeffit@millenia.cars.aps.anl.gov
http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit
--
Aimee M. Morey
Graduate Assistant
Department of Chemistry, U-3060
University of Connecticut
55 North Eagleville Rd
Storrs, CT 06269-3060
Phone # (860) 486 - 6567
Fax # (860) 486 - 2981
