[Ifeffit] Overlapping scattering paths

van der Veen Renske Renske.vanderveen at psi.ch
Sun Dec 16 03:08:00 CST 2007

Hello EXAFS experts,

I started using Athena and Artemis two weeks ago by applying it to the
EXAFS analysis of a moderately complicated molecule in solution. The
final fit is very good (R=0.006) but the errors on the fitting
parameters are very large and there are many high correlations between
parameters that shouldn't be correlated (even though I do multiple
k-weighted fitting). I think the problem is that there are at least 4
scattering pathways that overlap in the FT (spread in path lengths of
+-0.4 Angstrom). In addition, these scattering paths involve different
atoms and bonds, so that I have to define different delta_r and sigma_sq
parameters for all of them. 

My question is now: how could I reduce the error bars of the fitting
parameters that belong to these overlapping scattering paths? Or is it
hopeless without further information of the system?

Best regards,

Renske M. van der Veen
PhD student Chergui Group EPFL
Paul Scherrer Institut 
Swiss Light Source WSLA/210
5232 Villigen PSI

Phone: +41 56 310 5362
Fax: +41 56 310 3171
E-mail: renske.vanderveen at psi.ch
Web: http://lsu.epfl.ch

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