[Ifeffit] Imidazole multiple scattering in Artemis

[Robert Gordon]

Hi Chris,

Multiple scattering can be quite important, particularly in systems with 
higher local symmetry
(i.e. focused multiple scattering - many equivalent paths). It occurs 
along with back-scattering,
so you should include the Fe-N1 path. Conveniently, you can constrain 
the MS path based on
the back-scattering - i.e. the MS distance is dependent on the 
back-scatter distances and
scattering angle...you can also constrain the msrd (e.g. add in 
quadrature).

Prof. Dr. Thorsten Ressler's program "WinXAS" has the constraints as 
options built in...very convenient.

cheers,
-R.

On 2024-04-02 4:18 p.m., Chris Pollock wrote:
> 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
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> 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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