[Ifeffit] About S02

[Scott Calvin]

Hi Damdin,

Matt and Shelly have answered this very well, but I have one more  
thought to add.

You have a mineralogical sample and apparently have a pretty good idea  
what the mineral is, since you're not varying r or n. Under those  
circumstances, you probably have a hypothesis as to the structure  
beyond the nearest-neighbor. If you include more than one path in your  
fit, the inability to distinguish coordination number from S02 is  
reduced, and more importantly for your purposes, the correlation  
between S02 and sigma2 is also reduced. If it stays the same when you  
add more paths, it can help increase your confidence that the low S02  
in your fit is appropriate.

--Scott Calvin
Sarah Lawrence College

On Mar 27, 2009, at 9:19 AM, Zuzaan, Damdinsuren wrote:

> 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