[Ifeffit] XANES

Thu Mar 12 15:09:57 CDT 2009

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 at millenia.cars.aps.anl.gov
[mailto:ifeffit-bounces at 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
<Andreas.Voegelin at eawag.ch> 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 at 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 at millenia.cars.aps.anl.gov
		[mailto:ifeffit-bounces at 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 at 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/> 

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	-- 
	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