Freeze frame

Ice has as many as 14 formsnot many people would know that ice is found in as many as a dozen forms. The difference lies in the crystalline structure and density of the ice forms and is a result of variations in temperature and atmospheric pressure. Now, a team of scientists has discovered two more forms of ice, culminating a four-decade long search. Named ice xiii and xiv, they are formed at temperatures as low as minus 160 c .

Virtually all ice found on earth is of one form (called ice I_h), while the other forms are found in traces. With the discovery of ice xiii and xiv, "the way looks open to finally completing our knowledge of the crystalline behaviour of this amazing -- yet critically important -- simple molecule," says John Finney of University College London (ucl), who was a member of the team that discovered the previous ice form, ice xii.

The finding could help improve the understanding of the role of water in life-supporting chemical and biological processes, and could enhance computational models used in chemistry and structural biology. Further, the research team believes that the new ice forms may occur on the frigid moons of the outer planets of the solar system. Published in Science (Vol 311, No 5768, March 24, 2006), the study was conducted by a team from Oxford University in collaboration with the Council for the Central Laboratory of the Research Councils, and ucl .

Christoph Salzmann, one of the researchers, said theory had predicted the existence of the two new forms discovered. But the problem was how to achieve the low temperatures required. "We, therefore, had to search for a catalyst, which would encourage the phases (states) to form."

The scientists found that just a few drops of hydrochloric acid added to ice iii and some carefully applied pressure did the trick. The instruments at isis, the world's leading pulsed neutron facility in Oxfordshire, revealed the atomic structures. "Scientists have been searching for such a formation recipe for over forty years," says Finney.