Hi Gordon,
I have just one spectrum per sample, all taken at different T (unknown,
due to technical problems) and P (known). I'd like to find T and using
an EoS is not a viable option.
I was thinking that maybe, assuming that the Debye-Waller term is
explained only by thermal disorder, the Debye temperature is P
independent, and there are no structural or electronic transformations,
I could retrieve T by fitting the Debye-Waller term and using the
reference spectra. Is this possible?
It seems unlikely to me. XANES is typically described as probing the electronic states of a sample. There is, of course, a strong connection between atomic/nuclear structure and electronic structure, but the changes in thermal structural disorder with temperature are actually pretty small. Interference-sensitive measurements (EXAFS, XRD) will be sensitive to such changes, but XANES is much less so. When describing an EXAFS Deybe-Waller model, the amplitude decays as exp(-2k^2*sigma^2). When k is very small (ie, XANES), you need to have sigma be very large for that to make much of an impact in the XANES region.
Some XANES features (such as pre-edge peak intensities) can have some temperature dependence - these are sensitive to small changes in the overlap of specific electronic levels. But, in general, the XANES features don't have a strong temperature dependence.
But, I guess we should ask: do you see a significant variation in your XANES spectra with temperature?
--Matt