Structure of high-density amorphous water. I. X-ray diffraction study

X-ray diffraction measurements up to momentum transfer q = 16 Å-1 were performed at atmospheric pressure on both the high-density form of amorphous ice obtained by pressurization of crystalline ice Ih at 77 K up to 2 GPa and the low-density form obtained by further heating. These two amorphous phases exhibit significant differences at the level of the second- and third-nearest neighbors which involve a decrease of the O-O-O angle on compression at high pressure. Moreover, it is found that the low-density form is quite similar to that obtained by vapor deposition on cooled substrates at 77 K. © 1987 American Institute of Physics.