Resolution of interatomic distances in the study of local atomic structure distortions by energy-restricted x-ray absorption spectra

Applicability of the existing criteria for signal frequencies resolution to the problem of close interatomic distances determination by energy-restricted x-ray absorption spectra is studied within the approach based on the Fourier transformation and fitting procedures. Without losing generality, theoretical signals chi(k) of different k dependencies are used and among them-the signals chi(k) of x-ray absorption spectroscopy (k is the photoelectron's wave number). The last ones are calculated at different values of two interatomic distances R(1) and R(2) in a model of radial distribution of coordinating atoms in relation to the absorbing center, including the values of distances, which can't be resolved a priori according to the criteria. It is revealed that the boundary value of Delta R=vertical bar R2-R1 vertical bar, at which the model of local structure distortions can be distinguished among other alternative ones by the used approach depends strongly upon the coincidence of the functional form of k dependence used for the fitting function with that of the studied signal chi(k), well known in x-ray absorption spectroscopy. In the case of coincidence, the boundary value of Delta R obtained by the restricted intervals Delta k similar to 3 or 4 angstrom(-1) is approximately ten times smaller than that predicted by the existing criteria. The effect of statistical noise in spectrum intensity on the established Delta R value is analyzed.