At 03:07 PM 9/20/2005 +0200, you wrote:
I think the effect of interfering contributions in the Konigsberger and Prins. What I noticed, though, is that the fit of closer shells can affect that of the furthest shell because of the "spillof" from the first peak. The recciprocal I was not aware of. But I do agree with you on the whole. However, I think that in the FT case, these interences are limited to the nearest shells, whereas in k-space, nothing protects you from shells at, say, 2R and 3R (so to speak.
As part of a larger unpublished study that keeps sitting on my back-burner (one of these days maybe I'll finish up the paper and send it somewhere!), I looked at the seriousness of the "leakage" (or spill-over or interference or whatever you want to call it) from higher-R shells in a first-shell fit of fcc metals. Although I don't have the results at my fingertips right now, my recollection is that it was sufficient to completely screw up the dependence of lattice parameter and sigma2 on temperature for temperatures below room temperature. The fact that I've heard occasional assertions that EXAFS is not sufficiently sensitive to accurately yield the thermal expansion of fcc metals below room temperature suggests to me that some people may be underestimating the effect of this leakage. When the outer shells are accounted for (even crudely--no new free parameters are necessary), I found it relatively easy to get the right expansion characteristics. Having said that, of course the problem of leakage is LESS for fits in R-space than k-space, right? At least we're filtering out PART of the signal from outer paths when we do a fit on a portion of R-space, but that's not possible when we do a k-space fit. --Scott Calvin Sarah Lawrence College