Heterogeneous character of supercritical water at 400 °C and different densities unveiled by simulation

Interest is growing in the radiation science of supercritical water (SCW), yet how radiation energy is deposited still remains a question not well understood. To unveil the molecular structures of SCW, we carried out molecular dynamics simulations at 400 °C and different densities (0.17, 0.31, and 0.55 g cm−3). The results clearly show the heterogeneous character of these structures with coexisting high- and low-density regions. This water “clustering” behavior is consistent with observations in previous studies. It also supports the proposed role played by pre-existing polymeric clusters in the localization and hydration mechanisms of excess electrons in SCW. This underlying molecularity of SCW should be taken into account in track-structure chemistry models of SCW radiolysis.