Lower limit found for ice formation

Abstract

Ninety molecules—plus or minus 10—is the threshold at which nanosized water droplets can form ice crystals such as those we see in snowflakes or ice cubes, according to a new study (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1914254116). Previous theoretical studies put that lower limit at between 100 and 300 water molecules. Now, Valeria Molinero of the University of Utah, Francesco Paesani of the University of California San Diego, Thomas Zeuch of the University of Gottingen, and colleagues have combined experimental and theoretical work to find a more precise answer. The researchers generated water clusters of varying sizes at temperatures between 40 and 150 K using a high-pressure nozzle. Infrared spectroscopy revealed that crystalline-ice hydrogen bonds form between molecules in clusters of about 90 molecules and bigger at around 150 K. Up to about 150 molecules, the molecules in these clusters oscillate between the solid and liquid phases. The