Kinetic processes of interfacial transport of reactive species across plasma–water interfaces: the effect of temperature†

This work quantifies, through use of molecular dynamics (MD) simulations, the kinetic rates of physical surface processes occurring at a plasma–water interface. The probabilities of adsorption, absorption, desorption and scattering were computed for O₃, N₂O, NO₂, NO, OH, H₂O₂, HNO₂, HNO₃, and N₂O₅ as they interact with the interface at three water temperatures: 298 K, 323 K, and 348 K. Species are categorised into the short-residence group (O₃, N₂O, NO₂, and NO) and the long-residence group (OH, H₂O₂, HNO₂, HNO₃, and N₂O₅) based on their mean surface residence time. It is reported that the most probable process for the short-residence group is desorption, which limits their characteristic residence time at the interface to less than 100 ps, while the long-residence species experience a mixture of absorption and desorption, with a characteristic residence time exceeding 200 ps for many species in this group. With increasing water temperature, a universal decline in characteristic surface residence time is observed. It is found that the short-residence group experience a reduction in probability of desorption in favour of scattering, whereas the long-residence group experience a reduction in probability of adsorption in favour of absorption and desorption. The data reported in this work facilitate the development of a basic surface kinetic model, which was used to find that tuning the plasma toward the production of HNO₃ will result in an increase in the rate of uptake of reactive nitrogen species by a factor of 250%.