Formation of H2 on amorphous ice grains and their importance for planetary atmospheres

Details Formation of H2 on amorphous ice grains and their importance for planetary atmospheres Formation of H2 on amorphous ice grains and their importance for planetary atmospheres

Sep 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979ap%26ss..65...29s&link_type=abstract

(Lunar and Planetary Institute, Workshop on Thermodynamics and Kinetics of Dust Formation in the Space Medium, Houston, Tex., Se

Astronomy and Astrophysics

Astrophysics

8

Adsorption, Amorphous Materials, Hydrogen, Ice Nuclei, Interstellar Chemistry, Interstellar Gas, Planetary Atmospheres, Body Centered Cubic Lattices, Earth Atmosphere, Graphite, Hydrogen Atoms, Silicates, Solar System, Surface Reactions

Scientific paper

The mechanism and the rate of formation of H2 molecules from adsorbed H atoms on interstellar ice grains (or on ice coated non-icy grains) are investigated assuming that the ice is not crystalline but amorphous. Using the available theory and experimental data it is concluded that, in contrast to crystalline grains, the mobility of the adsorbed atoms on amorphous grains at temperatures of 10-20 K is exceedingly low so that the controlling factor is the probability that two H atoms are accidentally adsorbed within a site or two of each other. The rate of H2 forma- tion on ice grains per unit volume is much lower than previously estimated and is very sensitive to temperature. This conclusion applies not only to pure amorphous ice investigated here, but also to impure ice and to other grains (carbon or silicates) which would not be crystalline, such as graphite, but may be highly imperfect or actually amorphous aggregates of atoms or molecules. it is further shown that the presence of amorphous ice and clathrate grains in the early solar system would play a significant role in our understanding of the compositional anomalies in the Earth's atmosphere. The lifetime of these grains would be strongly affected by the absence of crystallinity

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