What defines a ‘new form’ of a substance? The question is provoked by a study showing the familiar, bent water molecule with its protons delocalised over no fewer than six equivalent positions around a ring, averaging away its dipole moment. Alexander Kolesnikov of Oak Ridge National Laboratory in Tennessee and colleagues call this a ‘new form of water’.
It sounds almost unbelievably odd. But the basic phenomenon reported by Kolesnikov and colleagues has in fact been recognised for decades. They have used neutron scattering to probe water molecules undergoing quantum tunnelling between different orientations while trapped in the molecular-scale channels of a crystal of beryl (Be3Al2Si6O18), which have a hexagonal cross-section. This tunnelling means that the lowest energy state of the molecules under the ultracold conditions of the measurements—around 5K—is a mixture of orientations in the six-fold symmetry of the channel.
This ground state is split into distinct energy levels by the tunnelling transitions, and the researchers see transitions between, revealed as resonant energy peaks in the neutron spectrum, as the neutrons exchange energy with the water molecules. ‘These results indicate that water in beryl at low temperature has an unusual shape, with delocalised protons over six positions,’ Kolesnikov says.
To read more, click here.