On 02/26/2014 08:23 AM, RAFAYAHER@alum.us.es wrote:

Hello,

I have been analyzing some EXAFS data with Artemis, and I was wondering what are the 3rd and 4th parameters in the path parameters window.

Hi Rafael, Those are the third and fourth cumulants of the absorber-scatterer distribution. They are best thought about in relation to the deltaR and sigma^2 parameters. Remember that we always measure EXAFS at finite temperature. That means that, even in a very well ordered material, there is thermal motion. In other materials there may be static sources of disorder as well. DeltaR is the centroid of the distribution of distances at which the scatterer is observed. sigma^2 is the mean square deviation in that distance. In the case of thermal motion, sigma^2 measures how much the scatterer is "jiggling" about it's average position due to thermal energy. The third cumulants is next higher moment of that distribution and the fourth is simply related to the fourth moment. Some reading material on this topic: http://dx.doi.org/10.1016/0167-5087(83)90655-5 http://dx.doi.org/10.1103/PhysRevB.46.687 http://dx.doi.org/10.1103/PhysRevB.48.585 Those will ground you in the theory and math of the cumulant expansion in EXAFS. There are literally thousands of examples of papers in the literature where the 3rd and 4th cumulants are included in the analysis. B -- Bruce Ravel ------------------------------------ bravel@bnl.gov National Institute of Standards and Technology Synchrotron Science Group at NSLS --- Beamlines U7A, X24A, X23A2 Building 535A Upton NY, 11973 Homepage: http://xafs.org/BruceRavel Software: https://github.com/bruceravel