Hi Matt
Now, if I have two samples and determined the S02 value according to the way which Bruce has in his supplement to the FEFFIT course,
How do you mean this? Is this the 'plot three curves of sigma2 v. S02 curves for three different k-weights' again? I find this approach puzzling and dangerous. I do not understand why the slope (correlation) of sigma2 v. S02 should depend on k-weight in any systematic way -- does anyone else know why it should?? What you want is the S02 and sigma2 that gives the lowest chi-square, not where these lines cross.
I have found that usually there is a "larger than one would like" correlation between the amplitude and phase terms in the EXAFS equation. But the different terms have different k-dependencies. Low k-weights will give more weight to an accurate E0, whereas higher k-weights will give a more accurate deltar. Although the errors will be large. If you plot the dependence of these variables on the k-weight, or better yet use all three k-weights in the fit, you will find that the best-fit value is consistent with the one k-weight value but that the uncertainty is lower because you are distinguishing between the two coorelated variables by including the k-dependence in the fit. Shelly