2019/12/17 by Johannes Fiedler, Mathias P. Bostrom, Fiedler, Johannes +11 · 2 citations
Engineering · Earth and Planetary Sciences · #Freezing and Crystallization Processes #Climate change and permafrost #Icing and De-icing Technologies
paper · pdf · doi:10.48550/arxiv.1912.08118
In view of the vital role of water in chemical and physical processes, an\nexact knowledge of its dielectric function over a large frequency range is\nimportant. In this article we report on currently available measurements of the\ndielectric function of water at room temperature (25\∘C) across the\nfull electromagnetic spectrum: microwave, IR, UV and X-ray (up to 100 eV). We\nprovide parameterisations of the complex dielectric function of water with two\nDebye (microwave) oscillators and high resolution of IR and UV/X-ray\noscillators. We also report dielectric parameters for ice-cold water with a\nmicrowave/IR spectrum measured at 0.4^\∘C, while taking the UV spectrum\nfrom 25\∘C (assuming negligible temperature dependence in UV). We\nillustrate the consequences of the model via calculations of van der Waals\ninteractions of gas molecules near water surfaces, and an assessment of the\nthickness of water films on ice and ice films on water. In contrast to earlier\nmodels of ice-cold water, we predict that a micron-scale layer of ice is\nstabilised on a bulk water surface. Similarly, the van der Waals interaction\npromotes complete freezing rather than supporting a thin premelting layer of\nwater on a bulk ice surface. Density-based extrapolation from warm to cold\nwater of the dielectric function at imaginary frequencies is found to be\nsatisfactory in the microwave but poor (40% error) at IR frequencies.\n