[Ifeffit] XANES pre-edge peak intensities

[vikrai at comcast.net]

Hi Paul 
It's a good question. 
I did not work with Fe pre-edge too much, I know better the situation with early 3d metals like Ti or V which have 3d^0 configuration. For these spectra the answer for your question is yes, pre-edge may depend on metal concentration. 
There are three mechanisms contributing to pre-edge formation. 
1. Quadrupole transitions 1s->3d. Intensities of corresponding peaks depend only on electronic configuration of absorbing atoms. 
2. Dipole transitions 1s->p states of absorbing atom hybridized with 3d states of the same atom. This hybridization (which is usually called p-d mixture) depends on the nearest environment of absorbing atom and gives information about its geometry. Intensities of these transitions also do not depend on concentration of absorbing atoms. But be careful, they depend on electronic configuration of those atoms i.g. low-spin or high-spin state. 
3.Dipole transitions 1s->p states of absorbing atom hybridized with 3d states of neighboring transition metal atoms. These transitions were observed in perovskite structure solid solutions and there intensities obviously depended on concentrations. 


The relative weights of these th ree contributions depend on situation. 


If you are interested I can send you a list of references. 


Best regards. 


Victor Krayzman 





Dear Ifeffit forum users 



I have been working on a batch of Fe K-edge XANES data for dilute glasses some time and I have extracted pre-edge peak positions and intensities, as has been widely used in the literature, to get qualitative analysis of the Fe coordination in my samples. I have also done this for a number of mineral "standards", again as has widely been done in the literature (Grandidierite, Yoderite, Staurolite, etc). However, I have a question: as my samples are considerably more dilute (ca. 0.15 mol% Fe) than all of the mineral standards (these vary in Fe content between a few percent and 10's of percent), how realistic is it to use mineral standards such as these to provide reference points to "calibrate" the integrated pre-peak intensities from the dilute samples? 

I have found nothing conclusive on this in the literature and would ask this forum for help, or any thoughts you may have on this issue. My own feeling is that concentration will have an effect on integrated pre-edge intensities and I suspect that more dilute samples are likely to give slightly higher integrated intensities than concentrated samples, but it is difficult to unpick and any thoughts or useful references dealing with such issues would be most welcome. 

Many thanks in advance for taking the time to read this message and thanks for your responses! 

Kind Regards 


Paul Bingham 

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