Scientists find molecular-level evidence for two structures in liquid water
Researchers found molecular-level evidence confirming two distinct structural arrangements in liquid water, settling a long-standing debate. The discovery explains water's unique properties and has implications for chemistry and biology.
Background
- For decades, the standard model of liquid water assumed it is a single, uniform phase — a "random network" of hydrogen-bonded molecules. This paper provides evidence that liquid water actually contains two distinct local structural environments at the molecular level.
- The researchers used advanced X-ray spectroscopy (X-ray Raman scattering) at a synchrotron facility to probe how water molecules are arranged. They found that water molecules exist in either a tetrahedral, ice-like structure (low-density) or a more disordered, high-density arrangement, and that these two motifs coexist in liquid water at ambient conditions.
- This work supports a controversial hypothesis called the "two-state" or "liquid-liquid critical point" model of water, first proposed decades ago. If confirmed, it would reshape our understanding of water's anomalous properties (its density maximum at 4°C, its high heat capacity, etc.) and have implications for climate science, biology, and chemistry.