Reactions of water molecules in silica-based network glasses

Given that H2O dissolves minimally in quartz, the mechanism for the ubiquitous dissolution of H2O in silica glasses has been a long-standing puzzle. We report first-principles calculations in prototype silica glass networks and identify the ring topologies that allow the exothermic dissolution of H2O as geminate Si-O-H groups. The topological constraints of these reactions explain both the observed saturation of Si-O-H concentrations and the observed increase in the average Si-Si distance. In addition, calculations of H2O and Si-O-H dissociation account for the observed response to radiation by wet thermally grown SiO2.