H/sub 2/ recombination on interstellar grains

Journal Article · Thu Jul 01 04:00:00 EDT 1976 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/154477· OSTI ID:7342853

Barlow, M J; Silk, J

From a consideration of relevant theoretical and experimental data it is concluded that H atoms (but not H/sub 2/ molecules) will be chemisorbed on interstellar graphite grains, with H/sub 2/ formation proceeding efficiently for graphite grain temperatures less than 70 K. It is argued that graphite grains will act as the principle sites for H/sub 2/ formation, with a formation rate of Rapprox. =4 x 10/sup -17/ cm/sup 3/ s/sup -1/. Heating by H/sub 2/ 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. We conclude that H/sub 2/ recombination will provide the largest heat source in diffuse clouds if the albedo of interstellar dust in the 912--1200 A region is high (approx.0.9), whereas if the albedo in this wavelength region is lower (approx.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. (AIP)

• Research Organization: Astronomy Centre, University of Sussex, England
• OSTI ID: 7342853
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 207:1; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640105* -- Astrophysics & Cosmology-- Galaxies
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ADSORPTION HEAT
ALBEDO
CARBON
CHEMICAL REACTIONS
CHEMISORPTION
CRYOGENIC FLUIDS
ELEMENTS
ENTHALPY
FLUIDS
GRAPHITE
HYDROGEN
INTERSTELLAR GRAINS
MOLECULES
NONMETALS
PARTICLES
PHYSICAL PROPERTIES
RECOMBINATION
SEPARATION PROCESSES
SORPTION
THERMODYNAMIC PROPERTIES