I meant to send this off to the list (instead I sent it to Scott Calvin only). Ahh the wonders of email. I thought I would parrot back something I read in one of Bruce's tutorials (that seemed to work well for me), namely that the Debye factor, sigma has a k dependence while S02 does not. This means that if you can Fourier isolate the first shell (and you can assume a coordination number), you can determine a value for S02 by a fit using different k weights. You simply fit sigma for various fixed values of S02 (e.g. 0.6 - 1.0) and repeat the process for different k weights (e.g. k, k^2, k^3). The resulting plot of sigma vs. S02 will result in a straight line for a given k weighting. The three different k weights will intersect at a single point (or almost so) and the value of S02 at this point will be the value of S02 for the sample. While we are discussing S02, I thought I would ask a little more about it myself. 1. S02, the passive electron reduction factor is a term that encompasses many body effects, in particular the effect of the core hole. It is also as such said to have a "weak energy and path dependence" [J.J. Rehr and R.C. Albers in Reviews of Modern Physics, v. 72, no. 3 (2000)]. The question is how fair is it to assume that S02 is a constant independent of shell, or in other words should S02 be allowed to vary with shell (e.g. with significant multiple scattering contributions?) 2. I don't remember the paper offhand, but as I recall, in a paper by Bruce, the value of S02 was ascribed a value greater than unity. I didn't grok the explanation at the time, and was wondering if Bruce (or anyone else) in his ever-expanding knowledge of exafs has an explanation for when/if S02 can be greater than unity. Certainly if you consider Rehr's definition of the overlap integral of the N-1 electron wavefunction with and without a core hole, the value of S02 cannot be greater than unity[same reference, p. 636]. Any comments?