[Ifeffit] k-weight in Artemis

[Scott Calvin]

At 11:42 AM 9/27/2006, Juan wrote:

>Scott, when I said "strange" spectra, I mean spectra very different (compared
>to k3) and with sharp valley between peaks.

Juan,

I teach at Sarah Lawrence College, where we like to insist that our 
students aren't strange, just different. :) In fact, that goes for 
the faculty too...our recruiting slogan is (no kidding): "You're 
different, so are we."

So the Fourier transform of a kwt 1 spectrum may look very different 
from the Fourier transform of a kwt 3 spectrum. There's nothing wrong 
or unusual about that. Remember: EXAFS Fourier transforms are not 
radial distribution functions, although they do correlate to them. 
You can't, for instance, equate the relative height of two peaks in 
the Fourier transform to the relative coordination number at two 
distances from the absorbing atom. On the other hand, if as a 
function of some external variable (time, temperature, 
concentration...) you see one peak go up while another goes down, you 
might hypothesize that there are changes in the average coordination 
number at two distances. But that hypothesis would have to be tested 
by modeling (e.g. Artemis/Ifeffit) or comparison to known 
standards--there are other phenomena that could be causing the change 
in the peak heights.

--Scott Calvin
Sarah Lawrence College