At least 275 water molecules needed to form an ice crystal

 

In idle moments I contemplate on strange things such as the origins of water on earth (which is largely unknown) and the life-span of water molecules (in the order of milliseconds) and the manner  in which water molecules are added to or lost from the apparently constant amount of water on earth. None of these questions are illuminated further but this interesting paper by researchers in Germany and the Czech Republic describes a technique for studying clusters of water molecules and provides some answers on the formation of ice crystals.

A Fully Size-Resolved Perspective on the Crystallization of Water Clusters by Christoph C. Pradzynski, Richard M. Forck, Thomas Zeuch, Petr Slavíček, Udo Buck . Science 21 September 2012:
Vol. 337 no. 6101 pp. 1529-1532 DOI: 10.1126/science.1225468

ABSTRACT

The number of water molecules needed to form the smallest ice crystals has proven challenging to pinpoint experimentally. This information would help to better understand the hydrogen-bonding interactions that account for the macroscopic properties of water. Here, we report infrared (IR) spectra of precisely size-selected (H2O)n clusters, with n ranging from 85 to 475; sodium doping and associated IR excitation–modulated photoionization spectroscopy allowed the study of this previously intractable size domain. Spectral features indicating the onset of crystallization are first observed for n = 275 ± 25; for n = 475 ± 25, the well-known band of crystalline ice around 3200 cm−1 dominates the OH-stretching region. The applied method has the potential to push size-resolved IR spectroscopy of neutral clusters more broadly to the 100- to 1000-molecule range, in which many solvents start to manifest condensed phase properties.

Illustrations of the molecular structure of three water clusters

Illustrations of the molecular structure of three water clusters : from http://physicsworld.com/cws/article/news/2012/sep/21/how-many-water-molecules-does-it-take-to-make-ice

 

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