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Conditions for condensation and preservation of amorphous ice and crystallinity of astrophysical ices

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Title: Conditions for condensation and preservation of amorphous ice and crystallinity of astrophysical ices
Authors: Kouchi, A. Browse this author
Yamamoto, T. Browse this author
Kozasa, T. Browse this author →KAKEN DB
Kuroda, T. Browse this author
Greenberg, J.M. Browse this author
Keywords: molecular processes
solar system: formation
stars: circumstellar matter
interstellar medium: clouds
Issue Date: Oct-1994
Publisher: EDP Sciences
Journal Title: Astronomy and Astrophysics
Volume: 290
Start Page: 1009
End Page: 1018
Abstract: Conditions for formation and preservation of amorphous ice formed through condensation of water vapor on a substrate is investigated both theoretically and experimentally. The kinetic consideration of deposition of vapor leads to the condition for formation of amorphous ice on a cold substrate: the flux of water vapor onto the substrate should be larger than a critical flux D_s/a^4 ≡ F_c, where D_s is the surface diffusion coefficient of water molecules on the substrate and a the lattice constant of the substrate. The validity of the derived condition has been confirmed by measuring the critical flux of water vapor onto a substrate of polycrystalline cubic ice as a function of temperature. From the measured F_c, a surface diffusion coefficient of H2O molecules on polycrystalline cubic ice has been determined. With regard to the preservation condition, we derive a theoretical expression of the time scale t_c for crystallization of amorphous ice, which has the same form at low temperatures as the empirical formula used so far. A self-diffusion coefficient of amorphous ice is estimated from a comparison between the theoretical and empirical formulas of t_c. The results are applied to condensation of ice in molecular clouds, circumstellar envelopes of late-type stars, and the primordial solar nebula. Discussion is given on the crystallinity of ices in these sites.
Rights: © 1994 ESO
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 小笹 隆司

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