The authors studied the structure and dynamics of individual water dimer and trimer on Cu(110) by using a scanning tunneling microscope (STM) and density functional theory (DFT). The dimer consists of hydrogen-bond donor and acceptor molecules, and dynamically rearranges the hydrogen bond resulting in the interchange of their roles. The large isotope effect (∼60) was founded in the interchange rate between (H2O)2 and (D2O)2, suggesting that the process involves quantum tunneling. The interchange motion was enhanced upon the excitation of an intermolecular mode that correlates with the reaction coordinate. In contrast, the water trimer was imaged as a static triangular shape. The calculation revealed that it forms a hydrogen-bond chain along the atomic row.
