# Atomic-scale structure analysis of a molecule at a (6-nanometer)$^3$ ice crystal

## TL;DR

This paper demonstrates nanoscale NMR spectroscopy of an ice crystal, revealing intra-molecular proton interactions and enabling detailed structural analysis of single water molecules at the nanometer scale.

## Contribution

It achieves the first detection of NMR spectra from a 6-nanometer cube of ice, resolving intra-molecular proton interactions for structural insights.

## Key findings

- Detected NMR spectrum from a 6-nanometer ice crystal
- Resolved intra-molecular proton dipolar interactions
- Derived water molecule bond orientation and length

## Abstract

Water is the most important solvent in nature. It is a crucial issue to study interactions among water molecules. Nuclear magnetic resonance (NMR) spectroscopy is one of the most powerful tools to detect magnetic interactions for the structure analysis of a molecule with broad applications. But conventional NMR spectroscopy requires macroscopic sample quantities with hampers in investigating nanoscale structures. Through quantum control of a single spin quantum sensor, magnetic resonance spectroscopy of nanoscale organic molecules and single molecules has been achieved. However, the measurement of the dipolar interaction of nuclear spins within a molecule at nanoscale and the analysis of its structure remain a big challenge. Here we succeed in detecting the NMR spectrum from an ice crystal with (6-nanometer)$^3$ detection volume. More importantly, the magnetic dipolar coupling between two proton nuclear spins of a water molecule was recorded. The resolved intra-molecule magnetic dipolar interactions are about 15 kHz and 33 kHz with spectral resolution at a few kHz. Analysis of the interaction-resolved NMR spectroscopy provides a spatial view of nanoscale ice crystal, from which the orientation of a water-molecule bond is derived and further the length of the bond can be got. This work enables NMR spectroscopy applications in single molecule structure analysis, provides a further tool for nanocrystalline and confined water research.