Final Report Summary - SULIWA (Deeply Supercooled Liquid Water) Water is different. It shows more than 70 anomalous properties, and it is the one substance believed to be key to the evolution of life. In spite of more than 100 years of research on this substance known to everyone, new fascinating properties are still b eing revealed by scientists. The project "Deeply SUpercooled LIquid WAter" (SULIWA) was devoted to studying non-crystalline forms of water known as "amorphous ices" or "glassy water". One of the most spectacular results of the project is the observation of an unknown, high-density liquid form of water above -157°C. This is the lowest temperature ever at which bulk liquid water has been observed. Amorphous ice is ubiquitous in space - by contrast to the Earth, on which the only solid form of water known is crystalline hexagonal ice, which can be found in winter on the ski-slopes or in the freezer at home - and so the new form of water unraveled in the SULIWA project may occur in astrophysical environments and may serve as reaction medium for the chemical reactions generating new molecules and as a cryoprotectant for protecting these chemical species from destruction by hard radiation. At -130°C this liquid may even co-exist with a second, low-density liquid phase of bulk H2O. This observation - called liquid polymorphism - might indeed be the key to the question why water is so anomalous, why ice floats on water or why water shows a density maximum. In the five years of study the research team could only just scratch the surface of possible reaction that may take place at such low-temperatures. One, is the formation of clathrate-hydrates in vacuum conditions and the other is reaction producing carbonic acid from carbonates - both of these reactions, the inclusion of a guest molecule in an ice lattice, and the "simple" protonation reaction take place at about -130°C, which demonstrates that not all chemical reaction are too slow at such low temperatures. In future, more complex chemical reaction will be studied in these forms of water. Glassy water is not only important below -100°C, but also between 0°C and -80°C - temperatures of importance in Earth's atmosphere. The process of freezing liquid aqueous droplets or turning them into glasses was investigated in this project, with some surprising results. Depending on size these droplets may freeze twice - after the first freezing event, a liquid layer covers the frozen core of the droplet, and this second layer may either freeze or become a glassy layer upon further cooling. The brightness and the albedo of clouds is greatly different when crystalline ice, glassy water or thin liquid solutions are at the surface of the particles - and so SUILIWA also contributes to our understanding of cirrus clouds or polar stratospheric clouds and the microphysics and chemistry associated with these clouds. This is of great importance since the microphysics of clouds represents one of the greatest sources of uncertainty in our models of Earth's energy balance and climate.
