XAFS spectroscopy. I. Extracting the fine structure from the absorption spectra

TL;DR

This paper compares three techniques for extracting fine structure from X-ray absorption spectra, introducing a new criterion for smoothing parameter selection and emphasizing uncertainty estimation in the analysis.

Contribution

It proposes a new reliable criterion for smoothing parameter determination and a method to improve stability in XAFS data extraction, considering prior information and error estimation.

Findings

Experimental noise is smaller than background approximation errors.

Background errors dominate the variance in structural parameters.

The methods improve the reliability of XAFS analysis.

Abstract

Three independent techniques are used to separate fine structure from the absorption spectra, the background function in which is approximated by (i) smoothing spline. We propose a new reliable criterion for determination of smoothing parameter and the method for raising of stability with respect to k_min variation; (ii) interpolation spline with the varied knots; (iii) the line obtained from bayesian smoothing. This methods considers various prior information and includes a natural way to determine the errors of XAFS extraction. Particular attention has been given to the estimation of uncertainties in XAFS data. Experimental noise is shown to be essentially smaller than the errors of the background approximation, and it is the latter that determines the variances of structural parameters in subsequent fitting.