▎ 摘　　要

Water in confinement exhibits altered properties in molecular arrangement, bonding, and interaction with its neighboring environment, as compared to its bulk counterpart. In this work, periodically arranged D2O nano droplets of similar to 1 nm size on top of a graphene/iridium moire superstructure were investigated by Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) under ultra-high vacuum conditions at similar to 120 K. The IR bands of D2O clusters differ significantly from those observed for bulk D2O amorphous solid water or crystalline ice phases. Blue-shifted symmetric and asymmetric stretching bands with narrower band widths and modified band intensity ratios were observed, pointing to an enhanced internal order and a reduced nearest neighbor distance. Furthermore, two IR bands of "dangling" deuterium atoms were detected originating from threefold coordinated water molecules at the surface of the clusters and at their interface to the graphene layer. The latter arose only with the transition from the water clusters to an amorphous solid water layer. We propose that upon coalescence, opposing local dipoles trigger a hydrogen bond rearrangement at the interface. Our results represent a first step toward an atomistic understanding of water in confinement.