[Ifeffit] phase shift correction

Ravel, Bruce bravel at bnl.gov
Sun Dec 2 09:43:59 CST 2007

Hi Bindu,

> Why the peak in the Fourier transform of the experimental 
> spectrum is less than the actual one. 

The EXAFS equation is:

              N S02 F(K)
    chi(k) = ----------- exp(-2k^2 sigma^2) sin(2kR + phi(k))

In the oscillatory term, there is a piece that is the phase shift
associated with the scattering of the photoelectron.  When you do a
Fourier transform, the peak of the sin wave is not at R, rather it is
shifted by an amount that depends on the size of phi(k).

> Why it is required to include the scattering phase shift correction
> in the experimental one? As it is expected that the experimental one
> should show the actual bond length.

I think that what I wrote above answers this question as well.


 Bruce Ravel  ----------------------------------- bravel at bnl.gov

 National Institute of Standards and Technology
 Synchrotron Methods Group at Brookhaven National Laboratory
 Building 535A
 Upton NY, 11973

 My homepage:    http://cars9.uchicago.edu/~ravel
 EXAFS software: http://cars9.uchicago.edu/~ravel/software/exafs/

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