Supercooled Liquid Water Diffusivity at Temperatures near the Glass Transition Temperature

Isotopically layered amorphous solid water films were used to measure the diffusivity of deeply supercooled liquid water near the glass transition. The films, composed of separate H₂¹⁸O and H₂¹⁶O layers, were grown by vapor deposition at low temperature and then heated to observe the intermixing of the isotopic layers. Very slow heating rates (as low as 10^-4 K/s) were used to decouple the diffusion and crystallization processes to ensure that the observed intermixing occurred at temperatures that were well-separated from the onset of crystallization. Numerical simulations of the desorption spectra were used to extract the translational diffusivities. The diffusivities obtained in this paper are consistent with translational liquid-like motion at temperatures near and above the proposed <i>T</i>_<i>g</i> of 136 K. These findings support the idea that the melt of amorphous water, above its glass transition temperature is thermodynamically continuous with normal supercooled liquid.