[Ifeffit] white line intensity v. edge position in determiningoxidation state of Re

Sven L.M. Schroeder sven.schroeder at gnomikos.com
Mon May 21 17:31:42 CDT 2007


Another method to get information on oxidation states from near-edges was
used relatively commonly in the 1980s and early 1990s, but has gone out of
fashion since (can someone tell me why? Is the underlying physics flawed?).

You determine the ionisation potential (IP) by fitting the arctan step
background function simultaneously with Gauss/Lorentz lines for all the
near-edge resonances. The inflection point of the arctan corresponds to the
IP. Variations in the IP can be interpreted using the same considerations as
for binding energy shifts in XPS...

For example, for Au there is an almost perfectly linear relationship between
IP and oxidation state, from Au(-1) via Au(0) and Au(+1) to Au(+3) ! In this
case the correlation with oxidation state is a lot stronger than for white
line intensities and/or the now commonly used 'edge inflection points'...


Sven L.M. Schroeder (mailto:s.schroeder at manchester.ac.uk)

School of Chemical Engineering and Analytical Science (CEAS) & School of
Chemistry The University of Manchester PO Box 88 Sackville Street Manchester
M60 1QD United Kingdom


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> -----Original Message-----
> From: ifeffit-bounces at millenia.cars.aps.anl.gov 
> [mailto:ifeffit-bounces at millenia.cars.aps.anl.gov] On Behalf 
> Of Bruce Ravel
> Sent: 17 May 2007 21:36
> To: XAFS Analysis using Ifeffit
> Subject: Re: [Ifeffit] white line intensity v. edge position 
> in determiningoxidation state of Re
> On Thursday 17 May 2007, Edward L. Kunkes wrote:
> >  I am trying to determine the oxidation state of Re in PtRe 
> > nanoparticles catalysts supported on carbon. The ReLIII edge was 
> > measured before and after an in-situ reduction in hydrogen. 
> Can anyone 
> > suggest Which characteristic of the edge is more related to 
> oxidation 
> > state ? Is it the integrated white-line intensity or the 
> position of 
> > the edge(point of maximum derivative). The edge position of 
> the ReLIII 
> > edge of my particles is the same as that of Re foil, 
> however the white 
> > line instensity is significanty higher. For the non-reduced PtRe 
> > particles, the edge position is similar to that of ReO2 
> (with a larger white line intensity).
> I see that no one has responded to this, so I'll take a stab.
> Presumably you know what the end members -- Re metal and Re 
> oxide -- look like.  Can you do linear combination fitting of 
> the intermediate spectra to determine the average oxidation?
> B
> --
>  Bruce Ravel  ---------------------------------------------- 
> bravel at anl.gov
>  Molecular Environmental Science Group, Building 203, Room 
> E-165  MRCAT, Sector 10, Advanced Photon Source, Building 
> 433, Room B007
>  Argonne National Laboratory         phone and voice mail: 
> (1) 630 252 5033
>  Argonne IL 60439, USA                                fax: 
> (1) 630 252 9793
>  My homepage:    http://cars9.uchicago.edu/~ravel 
>  EXAFS software: http://cars9.uchicago.edu/~ravel/software/
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