[Ifeffit] phase problem copper
bravel at bnl.gov
Wed Jul 15 09:09:16 CDT 2015
On 07/14/2015 10:18 AM, Neeb, Matthias wrote:
> I have a standard exafs spectrum of copper K-shell and everything
> looks as expected (Chi(E), Chi(k), Chi(R), Chi(q) …) when using
> Demeter 0.9.21 .
> However the phase spectrum of (Chi(q)) appears quite different to
> literature (e.g. B.K. Teo, Inorganic Chemistry Concepts 9; Martens et
> al, PRB 17, p1481 (1979), i.e. positive slope, a factor of ~10 larger
> values on y-axis.
> Any reason why? Thanks for your answer in advance.
I imagine that the reason no one has attempted an answer to your
question is because it is not clear what your problem is. You did not
provide a picture to help explain the problem, you did not you provide
data or an Athena project file. So I don't know what you are looking
at, although I suppose it has something to do with figure 1 in the
Martens paper. Vague, open-ended questions tend not to get prompt,
That said, I can venture a few guesses. Some possibilities:
1. Is the k-weighting different?
2. Are you comparing the real part of chi(q) to the real part of
chi(q)? Or imaginary to imaginary?
3. The Fourier transforms in EXAFS are complex transforms. chi(k) is
a real measurement. A decision has to be made about whether the
chi(k) measurement occupies the real or imaginary part of the
function that is transformed. I do not know which convention
Martens used. In 1979, that convention may not have been
established yet, but it certainly is in Ifeffit, Larch, and
Demeter. The different convention would result in phase shifts.
Bruce Ravel ------------------------------------ bravel at bnl.gov
National Institute of Standards and Technology
Synchrotron Science Group at NSLS-II
Upton NY, 11973
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