Ice-VII-like molecular structure of ambient water nanomeniscus

Abstract

Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases. Although most phases have been well investigated down to the molecular level, the molecular structure of the nanomeniscus, a ubiquitous form of nanoscale water in nature, still remains unexplored. Here, we demonstrate that the water nanomeniscus exhibits the stable, ice-VII-like molecular structure in ambient condition. Surface-enhanced Raman spectroscopy on trace amounts of water, confined in inter-nanoparticle gaps, shows a narrowed tetrahedral peak at 3340\u2009cm-1\xa0in the OH-stretching band as well as a lattice-vibrational mode at 230\u2009cm-1. In particular, the ice-VII-like characteristics are evidenced by the spectral independence with respect to temperature variations and differing surface types including the material, size and shape of nanoparticles. Our results provide un unambiguous identification of the molecular structure of nanoconfined water, which is useful for understanding the molecular aspects of water in various nanoscale, including biological, environments.Ice-VII, the densest phase of ice, has been expected to exist only under extreme conditions, such as in Earth’s deep mantle. Shin et al. show spectroscopic evidence that ice-VII-like structures can also be found in water confined in the nanomeniscus between packed nanoparticles at ambient conditions.