The influence of experimental and model uncertainties on EXAFS results

We analyze EXAFS oscillations in k-space with the FEFF code to obtain main- shell distances R-nu and mean-square displacement parameters sigma (2)(i) f or all single and multiple scattering paths i in the shells nu up to a maxi mum shell radius R-max. To quantify the uncertainty in the determination of these model parameters we take into account experimental errors and uncert ainties connected with background subtraction, with the approximate handlin g of the electronic many-body problem in FEFF, and with the truncation of t he multiple scattering series. The impact of these uncertainties on the R-n u and sigma (2)(i) is investigated in the framework of Bayesian methods. We introduce an a priori guess of these model parameters and consider two alt ernative strategies to control the weight of the a priori input relative to that of the experimental data. We can take a model parameter space of up t o 250 dimensions. Optionally we can also fit the coordination numbers N-j ( j less than or equal to nu) and the skewness of the distribution of the R-n u besides the R-nu and sigma (2)(i). The method is applied to 10K Cu K-edge and 300K Au L-3-edge data to obtain model parameters and their a posterior i error correlation matrices.