Full-Spectrum High-Resolution Modeling of the Dielectric Function of Water

Abstract

In view of the vital role of water in chemical and physical processes, an exact knowledge of its dielectric function over a large frequency range is important. In this article we report on currently available measurements of the dielectric function of water at room temperature (25 • C) across the full electromagnetic spectrum: microwave, IR, UV and X-ray (up to 100 eV). We provide parameterisations of the complex dielectric function of water with two Debye (microwave) oscillators and high resolution of IR and UV/X-ray oscillators. We also report dielectric parameters for ice-cold water with a microwave/IR spectrum measured at 0.4 • C, while taking the UV spectrum from 25 • C (assuming negligible temperature dependence in UV). We illustrate the consequences of the model via calculations of van der Waals interactions of gas molecules near water surfaces, and an assessment of the thickness of water films on ice and ice films on water. In contrast to earlier models of ice-cold water, we predict that a micron-scale layer of ice is stabilised on a bulk water surface. Similarly, the van der Waals interaction promotes complete freezing rather than supporting a thin premelting layer of water on a bulk ice surface. Density-based extrapolation from warm to cold water of the dielectric function at imaginary frequencies is found to be satisfactory in the microwave but poor (40% error) at IR frequencies.

Self-consistent dielectric functions of materials: Toward accurate computation of Casimir–van der Waals forces

“…Among them, the deviation observed for the data presented by Fiedler et al . ( 18 ) originates from the overestimation of ε 2 below the bandgap of water. The model proposed by Parsegian ( 30 ) predicts accurate values for the refractive indices, but only due to the underestimation of ε 2 at photon energies above 20 eV.…”

“… ( A ) The imaginary part of the dielectric function of water in the VUV region reported by several groups ( 14 , 15 , 17 , 18 , 30 ). ( B ) The refractive indices of water in the visible region calculated using the K-K analysis of the optical data are presented in (A).…”

Premelting of ice adsorbed on a rock surface

“…[1] As noted the theory presented in our work enables studies in multilayered systems where more than one film thickness can be varied. However, it should be stressed that very small changes in dielectric functions for water or ice (originating for instance from impurities, [4,26] presence of salt ions, [4,16,5] or from modelling based on a different set of optical data [99]) could influence the results, such as where premelting and ice formation near interfaces will occur. This sensitivity comes from the closeness of dielectric functions for ice and water as was pointed out many years ago by Elbaum and Schick.…”

Analysis of Emission Infrared Spectra of Protein Solutions in Low Concentrations

“…In this work, the emission spectra of solutions were measured in the mid-IR frequency range. It is obvious that the wider the spectral range, the more complete information on the substance structure can be obtained [22]. The expansion of the spectral range toward higher frequencies is problematic due to the need to heat the sample [1].…”