X-ray experiments reveal two different types of water

The strangest liquid of all is even more unusual than we thought

Liquid water exists in two different forms – at least at very low temperatures. This is the conclusion drawn from X-ray experiments carried out at DESY and at the Argonne National Laboratory in the US. An international team of researchers headed by the University of Stockholm now reports its findings in the Proceedings of the National Academy of Sciences (PNAS).

The scientists led by Anders Nilsson had been studying so-called amorphous ice. This glass-like form of frozen water has been known for decades. It is quite rare on earth and does not occur in everyday life; however, most water ice in the solar system actually exists in this amorphous form. Instead of forming a solid crystal – as in an ice cube taken from the freezer – the ice takes on the form of disordered chains of molecules, more akin to the internal structure of glass. Amorphous ice can be produced, for example, by cooling liquid water so rapidly that the molecules do not have enough time to form a crystal lattice.

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Picture: Liquid water has two variants: High Density Liquid (HDL) and Low Density Liquid (LDL) which have now been observed at extremely low temperatures, but can not be bottled. Photo: Gesine Born, DESY