Observation of Liquid-Liquid Transitions in the Hydrogen Bond Network of Water in "No-Man's Land" at Ambient Temperature and High Pressure

Abstract The liquid–liquid transition (LLT) in supercooled water is one of the most discussed topics in explaining the anomalous properties of water. Direct evidence of the LLT is challenging because of spontaneous crystallization in the deep supercooled region of the phase diagram. Here, combining diamond anvil cell technology with 2D-IR spectroscopy, we measured the fluctuation dynamics of hydrogen bonds in water and the conformation changes induced by changes in pressure at a room temperature of 23°C. The abrupt transition behavior at critical pressures is directly observed for the first time. Based on the deep-going theoretical simulations, this rapid onset is attributed to the collapse of linear hydrogen bonds within the tetrahedral configurations of water at the critical point. This transition provides valuable new insight in understanding the nature of water in the so called “no-man's land” for following the structural dynamics of water.