[Ifeffit] Split white line in TcO2 spectra and similar Tc(IV) octahedral environments

[Wayne Lukens]

Hi Fred,

The second resonance is due to scattering, mainly the multiple scattering
path involving the trans oxygen ligands of the octahedral Tc coordination
sphere, I believe. In other words, it is the beginning of the EXAFS
spectrum. These features are particularly prominent for Tc.

This is the characteristic XANES spectrum of Tc(IV) in an octahedral
environment with O neighbors.

Sincerely,

Wayne

ps If you look at the theoretical scattering curves from Feff, you can
identify which scattering path is responsible for this peak. If I recall
correctly, it is the path that I mentioned, but I may misremember.


On Mon, Aug 5, 2013 at 11:40 PM, <fred.mosselmans at diamond.ac.uk> wrote:

>  Hi,****
>
> ** **
>
> Tc(IV) which is a d3 configuration ion, when octahedrally coordinated by O
> ligands eg TcO2 has what I would call a split white line (see attached
> image) in the K-edge XANEs. Others might call it a very strong second
> resonance .  The image is from TC in an iron oxide phase by the way.****
>
> One of my collaborators asked me why does the edge have two peaks.?****
>
> This is a simple question but is there a simple answer? In a literature
> search although the shape seems accepted I couldn’t find a straightforward
> explanation.****
>
> Ce(IV) L3 spectra have a split white line due to some sort of crystal
> field effect but there the transition (L3-edge) is direct to d states so
> it’s a bit more obvious. Here it’s an s-p transition formally so you’d
> think it must be some sort of split p state explanation , but I am not sure
> why?****
>
> I am sure you could XANES simulate this to reproduce it but that doesn’t
> answer the question why in simple terms. It may be it ‘s a complicated band
> structure explanation and so  there is no simple answer but if anyone has
> read or knows one , I ‘d be interested,.****
>
> There are some similar effects in the white lines of Zr K-edge spectra ,
> when the Zr is also octahedral but I can only find reports of that not the
> reason for it. ****
>
> BTW This is definitely pure Tc(IV) so the answer is not multiple oxidation
> states., which has been used to explain different Tc split white lines in
> other situations.****
>
> Thanks****
>
> Fred****
>
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-- 
Wayne Lukens
Staff Scientist
Lawrence Berkeley National Lab
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