PNNL

Summary

The unusual properties of water compared to other liquids sustain life on Earth, yet there is still much to learn about this important liquid. For example, scientists wonder if water cooled far below its freezing point crystallizes “immediately” or equilibrates prior to crystallization. They also wonder if it exists as one broad distribution of states or a mixture of two distinct states. However, the rapid crystallization of supercooled water at ambient pressure and temperatures between 160K and 235K make it difficult to obtain experimental measurements to validate models.

Researchers at Pacific Northwest National Laboratory obtained a series of “snapshots” of the molecular structure of water in that temperature range. They saw two distinct structures—high-density and low-density liquids—that transitioned from one to the other reversibly with temperature. To make these measurements, the researchers warmed supercooled water films with nanosecond pulses of laser light and then captured structural information using infrared spectroscopy after the films had rapidly quenched back to low temperatures.