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Extracting the pair distribution function of liquids and liquid-vapor surfaces by grazing incidence x-ray diffraction mode

TitleExtracting the pair distribution function of liquids and liquid-vapor surfaces by grazing incidence x-ray diffraction mode
Publication TypeJournal Article
Year of Publication2008
AuthorsVaknin D, Bu W, Travesset A
Journal TitleJournal of Chemical Physics
Volume129
Pages044504
Date Published07
Type of ArticleArticle
ISBN Number0021-9606
Accession NumberISI:000258171500035
KeywordsINTERFACES, NEUTRON, ORIENTATION, POTENTIAL FUNCTIONS, SCATTERING EXPERIMENTS, simulation, spectroscopy, WATER-STRUCTURE
Abstract

We show that the structure factor S(q) of water can be obtained from x-ray synchrotron experiments at grazing angle of incidence (in reflection mode) by using a liquid surface diffractometer. The corrections used to obtain S(q) self-consistently are described. Applying these corrections to scans at different incident beam angles (above the critical angle) collapses the measured intensities into a single master curve, without fitting parameters, which within a scale factor yields S(q). Performing the measurements below the critical angle for total reflectivity yields the structure factor of the top most layers of the water/vapor interface. Our results indicate water restructuring at the vapor/water interface. We also introduce a new approach to extract g(r), the pair distribution function (PDF), by expressing the PDF as a linear sum of error functions whose parameters are refined by applying a nonlinear least square fit method. This approach enables a straightforward determination of the inherent uncertainties in the PDF. Implications of our results to previously measured and theoretical predictions of the PDF are also discussed. (C) 2008 American Institute of Physics.
DOI10.1063/1.2953572
Alternate JournalJ. Chem. Phys.