I was curious to tap the collective wisdom of those on the list regarding the "true meaning" of S02, the passive electron reduction factor, at least with regards to fitting experimental data to feff calculated paths. I understand that S02 is an aggregate "energy losses related to core hole creation parameter", but am curious about experimental data fitting. In particular, I have have started probing both high and low energy ranges for exafs and find that my usual experience from the 10-15 keV range don't seem to apply. In particular, I have been measuring energies around the O edge (540 eV) as well as some rather high energies edges Te (31 keV), Cd (26.7 keV) etc.. I have heard (indirectly via my coworker) from Andrei Rogalev that he considers S02 to be just another parameter. As the correlation between S02 and N is unity, this leads to a fair amount of ambiguity in the determination of coordination to say the least. While we are on the subject, are there any general observations about the transferablility of S02 from standards. How about the expected temperature dependence of S02? I do recall reading from John Rehr's article in RMP that S02 (which feff does calculate by the way) is an path dependent, complex sum that must be phasor summed. What are some realistic approximations/trends regarding to S02 and temperature, energy, and/or structure dependence? Dr. Paul Fons Senior Researcher National Institute for Advanced Industrial Science & Technology METI Optoelectronics Division Umezono 1-1-4 Tsukuba, Ibaraki JAPAN 305-8568