Structures of High-Density and Low-Density Water

The three site-site partial structure factors for water have been measured as a function of pressure, using neutron diffraction, at a temperature of 268 K. It is found that the measured structure functions imply a continuous transformation with increasing pressure from a low-density form of water ( ${\rho }_L\sim 0.0295\mathrm{molecules}/{Å}^3$), with an open, hydrogen-bonded tetrahedral structure, to a high-density form of water ( ${\rho }_H\sim 0.0402\mathrm{molecules}/{Å}^3$), with nontetrahedral O-O-O angles and a collapsed second coordination shell, which implies broken hydrogen bonds between the first and second coordination shells.