London: A team of scientists has determined that ice can be melted at –180 degree Celsius if the ice crystals contain just 48 water molecules.According to a report in New Scientist, Bernd von Issendorff at the University of Freiburg in Germany and his colleagues created ice clusters of just a few tens of water molecules, tagged with an extra electron.
The electron’s charge allowed the team to trap the clusters in electric fields and weed out those of the wrong size.
As the ice clusters were ten thousand times smaller than a grain of sand, the researchers couldn’t merely watch them melt.
Instead, at temperatures ranging from -265 degree C to -80 degree C, they triggered the evaporation of a few molecules with pulses of laser light.
By counting the number of molecules that evaporated, they could calculate the energy of each cluster before it was zapped.
Since liquids contain more energy than solids, they could deduce the temperature at which the clusters melted.
The researchers were surprised to find melting began at just under –180 degree C.
“Probably anybody would have guessed that a small amount of water behaves differently, but maybe not so many that it is so different,” said von Issendorff.
Von Issendorff and his colleagues expect their findings will fine-tune models that explain and predict cloud formation and climate, atmospheric chemistry, and the evolution of water-rich objects in outer space, such as fledgling comets.
First Published: Monday, July 27, 2009, 15:47