[Ifeffit] Truncating signal

Matt Newville newville at cars.uchicago.edu
Wed May 2 10:50:30 CDT 2018


Hi Julian,

On Wed, May 2, 2018 at 6:32 AM, Julian Ehwald <jehwald at gmail.com> wrote:

> Hi all,
>
>
>
> I have basic question on background removal in Athena. My data has some
> strong changes very close to the absorption edge, and if I start the
> background removal at k=0, the spline is not able to follow the signal for
> higher k-values (even at Rbkg=1.7 or similar). The background then
> oscillates slowly (4 A^-1) around my signal, generating huge peaks in the
> low regions of chi(R). If I set the spline range to begin at k=2.7 only
> (around 28eV above absorption edge) then I get rid of it. Now my question
> in general is, do I loose essential information about the nearest
> neighbours this way, respectively is that a common thing to do?
>
>
>
> Best, Julian
>
>
It should be fine to start the background as high as k=2.7 Ang^-1, though I
think most of find that we don't really need to do that very often.  You
will lose that part of the chi(k), but that part of the spectrum is really
XANES, and EXAFS analysis usually starts at around 2.5 to 3.0 Ang^-1
anyway.    And, since we typically k-weight by k, k^2, or k^3, that
de-emphasizes the low-k part of the spectrum anyway.  So, you don't really
lose much information about the near-neighbor coordination.

It might point to a different or weirder problem (you didn't say which edge
you were working with, or where on the spectrum E0 was set), but I'd say
that it is probably fine.

--Matt
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