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Infrared spectra of crystalline phase ices condensed on silicate smokes at T less than 20 KInfrared spectra of H2O, CH3OH, and NH3 condensed at T less than 20 K on amorphous silicate smokes reveal that predominantly crystalline phase ice forms directly on deposit. Spectra of these molecules condensed on aluminum substrates at T less than 20 K indicate that amorphous phase ice forms. On aluminum, crystalline phase H2O and CH3OH are formed by annealing amorphous deposits to 155 K and 130 K, respectively (or by direct deposit at these temperatures); crystalline NH3 is formed by direct deposit at 88 K. Silicate smokes are deposited onto aluminum substrates by evaporation of SiO solid or by combustion of SiH4 with O2 in flowing H2 followed by vapor phase nucleation and growth. Silicate smokes which are oxygen-deficient may contain active surface sites which facilitate the amorphous-to-crystalline phase transition during condensation. Detailed experiments to understand the mechanism are currently in progress. The assumption that amorphous phase ice forms routinely on grains at T less than 80 K is often used in models describing the volatile content of comets or in interpretations of interstellar cloud temperatures. This assumption needs to be reexamined in view of these results.
Document ID
19950030303
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Moore, Marla H.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Ferrante, Robert F.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Hudson, Reggie L.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Nuth, Joseph A., III
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Donn, Bertram
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 16, 2013
Publication Date
June 20, 1994
Publication Information
Publication: The Astrophysical Journal
Volume: 428
Issue: 2, pt
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
95A61902
Distribution Limits
Public
Copyright
Other

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