[Ifeffit] About S02

[Kelly, Shelly]

Hi Damdin,

S02 is 100% the same as the CN, the degeneracy, and the edge step
determined in the background removal process.  Your S02 is a bit on the
small side so I would check the edge step in Athena. I would also check
the CN used in the model by looking at the results page for each path.
This will report the combination of CN and SO2 and degeneracy.

I would fit a metal foil of the same element that you are looking at.  I
would use alpha*reff for the path lengths, one e0 value for all paths
and keep the CN/degeneracy fixed.  The metal foils usually give very
nice data and a reasonable S02, which I'd say goes from 0.7 to 1.1.  (So
you can see that not everyone even agrees on the acceptable range for
S02)

Unfortunately, everything may be done correctly and S02 of 0.64 may be
just what it is supposed to be. But I would look hard before coming to
that conclusion.  

I have a book chapter that you might get a lot of use out of.  If you
want a copy send me a request directly.  It is kinda big, 8Meg.  It
talks about how to set up the EXAFS models and how S02 is correlated to
all the other variables.  Using kw in the FT of 1, 2, and 3 also helps.
I'd also look at the low and high k-regions of your data and see if S02
depends on that too.  

Good luck,
Shelly

> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov [mailto:ifeffit-
> bounces at millenia.cars.aps.anl.gov] On Behalf Of Zuzaan, Damdinsuren
> Sent: Friday, March 27, 2009 8:19 AM
> To: 'ifeffit at millenia.cars.aps.anl.gov'
> Subject: [Ifeffit] About S02
> 
> Hello everyone,
> 
> I am graduate student and doing EXAFS in my research.
> 
> My question is about S02. From the XAFS books or theory it says that
this
> value must be between 0.8 to 1, but in the literature some people used
> different values like 0.25 or 1.4. In my case I fitted experimental
RDF of
> my standard sample by holding the known r and n values for each path,
> while varying E0, S02 and sigma2. Obtained E0 and S02 values were
holded
> for unknown sample and rest were floated freely. S02 were 0.64. So my
> question is that this relatively small S02 value could affect the
> mineralogical interpretations made in my study. Should I refit it
using
> high value? Thanks in advance
> 
> Regards,
> 
> Damdin
> 
> _______________________________________________
> Ifeffit mailing list
> Ifeffit at millenia.cars.aps.anl.gov
> http://millenia.cars.aps.anl.gov/mailman/listinfo/ifeffit