On Tuesday 20 March 2007 16:36, Richard Mayes wrote:
Basically, I have been asked to plot what Artemis gives for the theory when an individual path is plotted, except I'm supposed to do it for the raw data...that is, plot the individual paths that sum to the observed chi(k).
However, looking at the picture from some old rhodium dimer EXAFS given to me by the good guy that signs my checks ;-) (a pic I'm supposed to use as a guide), I'm "chasing a rabbit." Problem solved (it's a "use the theory, Homer" moment, i.e. DO'OH!).
Richard, I'm confused in the same way that Scott is. There is no way to deconstruct your chi(k) data into path components a priori. The only way that we have understanding data in a path-by-path manner is to compute some theory and plot each of the paths from the theory. Even better is to do a fit and plot each of the paths after the fitted parameters have been evaluated. It occurs to me that you may be thinking of Fourier filtering the peaks. That is done in Athena by placing an R window around some region of your chi(R) spectrum then pressing the "kq" button. A word of caution -- plotting a Fourier filtered spectrum is NOT the same thing as plotting a path. In certain situations, a path from Feff and the Fourier filter of a region of chi(R) might be very similar. Indeed, they might be sufficiently similar that the filtered spectrum can be interpretted as the contribution from a path. More often, however, that is a very flawed assumption. In any situation where two or more paths conbtribute to a peak in chi(R) (and excellent example would be the first peak in iron metal, which contains contributions from the first two coordination shells and which cannot be separated by Fourier filtering) it would be quite incorrect to call the filtered specutm a "path contribution". HTH, B -- Bruce Ravel ---------------------------------------------- bravel@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/