Ice: the laboratory in your freezer

Abstract

The water molecule may look simple, but the crystalline phases it can form show a complexity and subtlety of behaviour that is perhaps unrivalled by any other known molecule. At least twelve crystalline phases are known to exist, with several others suspected. The crystal structures can be rationalised in terms of the strength and geometry of the intermolecular interaction between molecules – the hydrogen bond – though there are additional complexities when we come to consider the disorder in molecular orientations (‘hydrogen disorder’) found in most structures. Furthermore, the restrictions imposed by the chemistry of the hydrogen bonding interaction prevent most of the disordered phases from ordering as temperature is lowered: most ice structures are in fact orientational glasses rather than genuinely ordered crystals. To the ice physicist and chemist, the ice system is a fertile laboratory in which to improve our understanding of the atomic level interactions that underlie much of chemistry, and that may well be central to life itself.