What a difference a D20 makes
7 Nov 2011 by Evoluted New Media
Water is one of the simplest and most abundant chemicals on the planet, but scientists are still working to unlock its secrets, including understanding its true structure.
An international collaboration has developed a new technique to explain the true structure of water, and the structural differences between H2O and D2O. The technique is based on the fact that oxygen isotopes – which are found in structurally disordered materials like silicates and glasses – have different neutron scattering lengths.
As neutrons pass through materials they are bounced by atomic nuclei, which alter their trajectories. These scattered neutrons can be detected to create detailed maps of the sample’s molecular structure.
It was generally assumed that the difference in scattering lengths between oxygen’s isotopes was too small, but using neutron interferometry – a technique where neutrons, acting as coherent quantum waves, allow for very precise measurements of the scattering length – researchers showed that the difference between two isotopes was six times larger than literature suggested.
“With this larger contrast, we showed this difference in the scattering lengths of the oxygen isotopes was just about large enough to make neutron scattering a plausible technique for studying the structure of oxide materials,” said Professor Philip Salmon from the department of physics at the University of Bath.
The team studied the structure of water, focussing on comparing the structural differences between light water and heavy water. Using oxygen isotope substitution, Salmon and his team analysed the difference between the O-h and O-D bonds in water molecules.
“The structure and dynamics of water have long been controversial subjects since they can have profound effects on biological processes, and there can be dramatic difference between heavy and light water,” said Dr Henry Fischer, a physicist at the Institut Laue-Langevin where the work was conducted.
Researchers found that O-H bonds were ½% longer than O-D bonds, marking the first time anyone had measured the important difference between the molecular structures of light and heavy water with such accuracy.
