The structure of supercritical heavy water as studied by neutron diffraction

Neutron diffraction experiments of heavy water at several supercritical states (380T500 °C and 200P900 bar) corresponding to densities ranging from 0.2 to 0.7 g/cm3 are performed. They allow the static structure factor and the pair correlation function to be derived once absorption, multiple scattering, and inelasticity corrections have been made. The experimental results are compared with previous data obtained by Postorino et al. Nature 366, 668 (1993) and with new molecular dynamics simulations using the extended simple point charge (SPCE) potential. They lead to the conclusion that hydrogen bonding is still present in supercritical water. This conclusion does not agree with the previous findings of Postorino et al. but looks rather in agreement with the results of computer simulations.