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Reversible structural transformations in supercooled liquid water from 135 to 245 K

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Science  18 Sep 2020:
Vol. 369, Issue 6510, pp. 1490-1492
DOI: 10.1126/science.abb7542

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Supercooled water structures

Water displays a number of anomalous properties that are further enhanced in its supercooled state, but experimental studies at ambient pressure must obtain data before the onset of rapid crystallization at temperatures below ∼240 kelvin. Kringle et al. obtained infrared spectra of supercooled water films at temperatures between 135 and 235 kelvin that formed for a few nanoseconds by ultrafast heating and cooling. Supercooled water thermally equilibrates before crystallization above 170 kelvin, and over the range of temperatures studied, the structure of water was shown to be a linear combination of a high-density and a low-density liquid.

Science, this issue p. 1490

Abstract

A fundamental understanding of the unusual properties of water remains elusive because of the limited data at the temperatures and pressures needed to decide among competing theories. We investigated the structural transformations of transiently heated supercooled water films, which evolved for several nanoseconds per pulse during fast laser heating before quenching to 70 kelvin (K). Water’s structure relaxed from its initial configuration to a steady-state configuration before appreciable crystallization. Over the full temperature range investigated, all structural changes were reversible and reproducible by a linear combination of high- and low-temperature structural motifs. The fraction of the liquid with the high-temperature motif decreased rapidly as the temperature decreased from 245 to 190 K, consistent with the predictions of two-state “mixture” models for supercooled water in the supercritical regime.

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