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H2 recombination on interstellar grains

BARLOW, MJ; SILK, J; (1976) H2 recombination on interstellar grains. Astrophysical Journal , 207 pp. 131-140. 10.1086/154477. Green open access

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From a consideration of relevant theoretical and experimental data it is concluded that H atoms (but not H2 molecules) will be chemisorbed on interstellar graphite grains, with H2 formation proceeding efficiently for graphite grain temperatures less than 70 K. It is argued that graphite grains will act as the principal sites for H2 formation, with a formation rate of about 4 to the minus 17th cu cm per sec. Heating by H2 molecules formed by surface recombination is analyzed in the context of the available experimental data, and a heating rate is derived and compared with other suggested cloud heating mechanisms. It is concluded that H2 recombination will provide the largest heat source in diffuse clouds if the albedo of interstellar dust in the 912-1200 A region is high (about 0.9), whereas if the albedo in this wavelength region is lower (about 0.5), photoelectron ejection from grains will tend to predominate, and can explain observed cloud temperatures with a carbon depletion factor of approximately 2, a factor attributable to a normal interstellar abundance of graphite grains.

Type: Article
Title: H2 recombination on interstellar grains
Open access status: An open access version is available from UCL Discovery
DOI: 10.1086/154477
Publisher version: https://doi.org/10.1086/154477
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Chemisorption; Gas Heating; Graphite; Hydrogen Clouds; Hydrogen Recombinations; Interstellar Matter; Abundance; Desorption; Gas Temperature; Hydrogen Atoms; Particle Energy; Photoelectric Emission; Surface Reactions; Astrophysics
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy
URI: https://discovery.ucl.ac.uk/id/eprint/10096233
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