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

[vikrai at comcast.net]

Hi Fred, 
If you want to get a simple answer, first, try to calculate XANES in TcO_6 octahedron only. If you reproduce the split the simple answer does exist though it may be not obvious. If the split is not reproduced in 7- atomic cluster the situation is worse. Try to increase the cluster and see what will happen. 
I am not sure that EXAFS approximation works sufficiently well for this energy region. 
Regards. 
Victor Krayzman 
MML. NIST. Gaithersburg 






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 





Prof. J F W Mosselmans 

Principal Beamline Scientist I18 

Diamond Light Source 

Diamond House 

Harwell Campus 

Didcot 

Oxon 

OX11 ODE 

UK 



T 00 44 1235 778568 

M 00 44 7785510211 

E fred.mosselmans at diamond.ac.uk 

F 00 44 1235 778448 



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