[Ifeffit] Imidazole multiple scattering in Artemis

[Chris Pollock]

Hi everyone,
I've been using Artremis for quite a while, but have only recently come
across a case where the inclusion of multiple scattering seems to be
important for fitting some data and wanted to ask what is probably a super
basic question to make sure I don't mess anything up.

I've recently collected some data on a metalloenzyme with a quite
histidine-rich active site and, since it's been shown previously that
multiple scattering is important for fitting the longer range scattering
for these types of systems, I wanted to make sure I capture this in my
Artemis fits.  The data appear to show scattering contributions from N3,
C2, and N1 in the imidazole ring, and FEFF seems to agree that those paths
are the most important, though it calculates the MS intensity to be
significantly greater than the single scattering for the farther N (N1).
So, my super naive question is:  To include multiple scattering paths in
the fits--say, the Fe-N3-N1 triangle--is it correct to include the Fe-N3-N1
multiple scattering path in addition to the Fe-N3 and Fe-N1 single
scattering paths, or would that effectively be double counting the farther
nitrogen (N1)?

Thanks in advance!
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