Journal article Open Access

Structural transitions in amorphous water ice and astrophysical implications

Jenniskens, P.; Blake, D. F.

Selected area electron diffraction is used to monitor structural changes of vapor-deposited water ice in vacuum during warm-up from 15 to 188 K. A progression of three amorphous forms of water ice is found with well-defined transitions. The formation of a high-density amorphous form (Iah) at 15 K is confirmed, and the transition to the more familiar low-density form (Ial) occurs gradually over the range 38 to 68 K. At 131 K, the ice transforms into a third amorphous form (Iar), which precedes the crystallization of cubic ice (Ic) and coexists metastably with Ic from 148 K until at least 188 K. These structural transformations of amorphous water ice can be used to explain hitherto anomalous properties of astrophysical ices. The structural transition from Iah to Ial is responsible for the diffusion and recombination of radicals in ultraviolet-photolyzed interstellar ices at low temperatures. The occurrence and persistence of Iar explains anomalous gas retention and gas release from water-rich ices at temperatures above 150 K.

Files (1.1 MB)
Name Size
1.1 MB Download
Views 115
Downloads 67
Data volume 75.6 MB
Unique views 111
Unique downloads 65


Cite as