Molecular beam techniques were used to create nanoscale thin films which were composed of different isotopes of amorphous solid water. The metastable composites were then heated to above the glass transition temperature and the extent of isotopic intermixing was determined by desorption. The self-diffusion at 150 to 160K was some 106 times higher than that expected for crystalline ice. The value and temperature-dependence of the self-diffusivity were consistent with an amorphous solid melting into a highly supercooled liquid before crystallization. The overall temperature dependences for the diffusivity of liquid water, supercooled liquid water (238 to 273K) and amorphous solid water (150 to 160K) were described by the Vogel-Fulcher-Tamman equation. The results suggested that amorphous solid water, above its glass transition temperature, was a highly supercooled metastable extension of normal liquid water before crystallizing at near to 160K. Rapid H/D isotopic exchange occurred at the same time as translational diffusive motion.

The Self-Diffusivity of Amorphous Solid Water near 150K. R.S.Smith, Z.Dohnálek, G.A.Kimmel, K.P.Stevenson, B.D.Kay: Chemical Physics, 2000, 258[2-3], 291-305