Quasiparticle Behavior Facilitates Long-Range H+/OH- Recombination in Water

The recombination of H3O+ and OH- ions is one of the most essential reactions occurring in water, whose microscopic mechanism of recombination unfortunately remains elusive due to the subnanosecond dynamics and subnanometer scales. Here, the detailed recombination mechanism is unraveled by molecular dynamics (MD) simulations driven by a reactive artificial neural network potential field. Nuclear quantum effects (NQEs) were explicitly incorporated with the framework of thermostated ring-polymer MD. The simulations reveal that long hydrogen bond wires (4 and 5 hydrogen bonds) contribute about half of the total recombination events, which was previously underestimated. Additionally, their ratio further increased as NQEs were included, indicating the non-negligible contribution of quantum effects. Further analysis demonstrates proton transfer in a quasiparticle manner across long hydrogen bond wires. This work establishes a long-range recombination paradigm for water, providing critical insights for the fundamental behavior of water.