Molecular Dynamics Simulation Reveals a Change in the Structure of Liquid Water Near 150 °C, which May Explain Apparent Anomalies in High-Temperature Water Radiolysis

SPC/E molecular dynamics simulations are used to examine the structure of liquid water as a function of temperature between 25 and 350 degrees C at a constant pressure of 25 MPa. Analysis of the calculated oxygen-oxygen (O-O) and oxygen-hydrogen (O-H) radial distribution functions shows that water undergoes a structural change around 150 degrees C, characterized by large drops in the O-O/O-H coordination numbers. This structural change could explain some apparent anomalies experimentally observed in the radiolysis of water at elevated temperatures. These include the thermalization distance of secondary subexcitation electrons and the rate constant of the bimolecular reaction of two hydrated electrons, both of which experience a sudden and sharp drop near 150 degrees C.