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Structure and dynamics of amorphous water iceFurther insight into the structure and dynamics of amorphous water ice, at low temperatures, was obtained by trapping in it Ar, Ne, H2, and D2. Ballistic water-vapor deposition results in the growth of smooth, approximately 1 x 0.2 micrometer2, ice needles. The amorphous ice seems to exist in at least two separate forms, at T < 85 K and at 85 < T < 136.8 K, and transform irreversibly from one form to the other through a series of temperature-dependent metastable states. The channels formed by the water hexagons in the ice are wide enough to allow the free penetration of H2 and D2 into the ice matrix even in the relatively compact cubic ice, resulting in H2-(D2-) to-ice ratios (by number) as high as 0.63. The larger Ar atoms can penetrate only into the wider channels of amorphous ice, and Ne is an intermediate case. Dynamic percolation behavior explains the emergence of Ar and Ne (but not H2 and D2) for the ice, upon warming, in small and big gas jets. The big jets, each containing approximately 5 x 10(10) atoms, break and propel the ice needles. Dynamic percolation also explains the collapse of the ice matrix under bombardment by Ar , at a pressure exceeding 2.6 dyn cm-2, and the burial of huge amounts of gas inside the collapsed matrix, up to an Ar-to-ice of 3.3 (by number). The experimental results could be relevant to comets, icy satellites, and icy grain mantles in dense interstellar clouds.
Document ID
20040142084
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Laufer, D.
(Tel Aviv University Israel)
Kochavi, E.
Bar-Nun, A.
Owen, T.
Date Acquired
August 22, 2013
Publication Date
December 15, 1987
Publication Information
Publication: Physical review. B, Condensed matter
Volume: 36
Issue: 17
ISSN: 0163-1829
Subject Category
Exobiology
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Exobiology
NASA Discipline Exobiology
Non-NASA Center
NASA Discipline Number 52-10

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