Water’s anomalous behavior becomes especially pronounced in the deeply supercooled regime, where rapid crystallization has long prevented direct structural investigation. In this talk, I present time-resolved electron diffraction experiments inside a TEM that define the kinetic boundaries separating vitrification, crystallization, and metastable liquid persistence, providing new insight into water’s structure in the so-called no man’s land.[1,2]

Using shaped microsecond laser pulses, we precisely measured the critical cooling rate required to vitrify pure water as 6.4 • 106 K/s, thereby resolving long-standing discrepancies in the literature.[3] In contrast, flash-heating amorphous solid water reveals that crystallization can still occur at significantly higher heating rates, unless they exceed a critical threshold of approximately 108 K/s.[4] These results establish both the lower and upper kinetic limits for maintaining water in an amorphous or liquid state.

Structural analyses further show how water transitions between the liquid and glassy states, and how these transitions differ between H2O and D2O. Deuterated water consistently exhibits greater structural order and sharper transitions, underscoring the impact of nuclear quantum effects on hydrogen bonding in water.

Our experimental approach offers a new access to water’s supercooled regime and helps unravel the dynamic and structural limits that govern its behavior in this metastable state.