Nearest-neighbor oxygen distances in liquid water and ice observed by x-ray Raman based extended x-ray absorption fine structure

Abstract

We report the nearest-neighbor oxygen-oxygen radial distribution function (NN O-O RDF) of room temperature liquid water and polycrystalline ice Ih (-16.8 degrees C) obtained by x-ray Raman based extended x-ray absorption fine structure (EXAFS) spectroscopy. The spectra of the two systems were taken under identical experimental conditions using the same procedures to obtain the NN O-O RDFs. This protocol ensured a measurement of the relative distance distribution with very small systematic errors. The NN O-O RDF of water is found to be more asymmetric (tail extending to longer distances) with longer average distance (2.81 A for water and 2.76 A for ice) but a slightly shorter peak position (2.70 A for water and 2.71 A for ice). The refinement also showed a small but significant contribution from the linear O-H-O multiple scattering signal. The high sensitivity to short range distances of the EXAFS probe will set further restrictions to the range of possible models of liquid water.

Time-resolved X-ray absorption spectroscopy of infrared-laser-induced temperature jumps in liquid water

“…We focus here on the near-edge region of the x-ray absorption spectrum (near edge x-ray absorption fine structure, NEXAFS [55]). While the extended high-energy region of the spectrum (extended x-ray absorption fine structure, EXAFS) can be used to extract O-O radial distribution functions [58,59], the near-edge region reflects how the local electronic structure of the absorbing molecules is affected by hydrogen bonding. It hence gives indirect access to the local structure of water.…”

Structural transformations in amorphous ice and supercooled water and their relevance to the phase diagram of water

“…It is also should be mentioned that a number of other approaches to determining structure can in principle be adopted, such as extended x-ray absorption fine structure (EXAFS) [24], but to date these have not been widely applied to the supercooled and amorphous states of water. Equally electron diffraction was once combined with neutron and x-ray diffraction to attempt to produce three datasets from which to extract the site-site radial distribution functions for water [25].…”

Microscopic structure of water at elevated pressures and temperatures

“…However, there is still no consensus on how to describe the microscopic structure of this elusive liquid (2)(3)(4). The most prominent methods of study are the determination of site-site correlation functions using neutron or X-ray diffraction (5)(6)(7)(8), the analysis of density fluctuations by small angle X-ray and neutron scattering (9)(10)(11), and the investigation of the oxygen's local environment by spectroscopic methods (2,3,10,12,13) providing controversial interpretations of the local atomic structure of water. This has resulted in an intense discussion of whether the microscopic structure of ambient water can be described as a liquid with homogeneous density (e.g., refs.…”