Hi Bruce, thank you very much for taking the time to write your helpful reply. As you mentioned,
This really gets at the heart of why exafs analysis is difficult. You are certainly correct that the deltaE0 is highly correlated with delR and C3. That correlation is hard to avoid in a non-linear analysis as all three terms effect the phase of the calculated chi(k).
That's exactly why I decided to post the question on the list asking for the advice of more experienced people who can certainly evaluate the question much better than myself. Also, I've always been trying to follow your "reasonable and defensible applied to all the parameters, not just e0" motto; another strong motivation for posting this question on the list. I don't know if it is just me, but in my short time working with EXAFS I got the strong impression that it is very easy to fall into the temptation of sophistry to get to the "expected" results from a fit. In this respect, I consider the mailing list an invaluable resource to help overcoming such a temptation. But coming back to the original question, would you say that analyzing a temperature-dependent set of the very same NC-containing sample (eight measurements between 10K and 300K) to get an E0 value would be a sound approach? Or should we expect E0 to vary with the temperature as well? Cheers, Leandro