Other
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.277o&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Other
Scientific paper
It is well known that H_2O is the most abundant solid component in interstellar icy grain mantles. Despite a numerous number of astronomical observations of H_2O ice in those environments, its formation mechanism has not been well understood. Although theoretical studies predicted that H_2O was formed on the surface of interstellar grains through sequential hydrogenation of atomic O, molecular O_2, and/or O_3, little study has experimentally demonstrated the formation of H_2O under astrophysically relevant conditions. In the present study, we investigated the formation of H_2O through sequential hydrogenation of O_2 on cold substrates (Al or amorphous D_2O ice) at 10--40 K. Two types of experiments were performed; one of which is hydrogenation of solid O_2, and another continuous codeposition of atomic H with gaseous O_2 on the substrate, in order to reveal the reaction kinetics and the structure of H_2O ice formed by reactions, respectively. Solid H_2O was found to form by surface reactions of O_2 with atomic H via formation of H_2O_2 as an intermediate product. We found that reactivity is enhanced on predeposited amorphous D_2O ice at high temperatures. The H_2O ice formed is amorphous phase but has a compact structure in contrast to vapor-deposited amorphous H_2O ice, which is well consistent with astronomical observations. The present study suggests that sequential hydrogenation of O_2 is one of the important route to the formation of H_2O in molecular clouds.
Chigai Takeshi
Hidaka Hiroshi
Kouchi Akira
Miyauchi N.
Oba Yasuhiro
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