HAC-coated silicate grains and PAHs in diffuse clouds and low-velocity shocks

Details HAC-coated silicate grains and PAHs in diffuse clouds and low-velocity shocks HAC-coated silicate grains and PAHs in diffuse clouds and low-velocity shocks

Dec 1989

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1989mnras.241..753b&link_type=abstract

Monthly Notices of the Royal Astronomical Society (ISSN 0035-8711), vol. 241, Dec. 15, 1989, p. 753-767. Research supported by N

Astronomy and Astrophysics

Astronomy

14

Cyclic Hydrocarbons, Interstellar Chemistry, Interstellar Gas, Molecular Clouds, Shock Wave Propagation, Silicates, Stellar Models, Amorphous Materials, Carbon, Hydrogenation, Oxidation, Oxygen Atoms

Scientific paper

A model is investigated in which hydrogenated amorphous carbon (HAC)-coated silicate grains subjected to low-velocity shocks release carbon to the gas in the form of atoms and PAHs. Both HAC and PAH are assumed to be subject to chemistry, including reactions with oxygen atoms, carbon atoms, and carbon ions. The released species contribute to a conventional post-shock chemistry, during which the HAC and PAHs may be further eroded or restored. It is found that the parameter of crucial importance is the reaction efficiency for atomic oxygen with both HAC and PAH. If this efficiency is less than 100 percent, then HAC mantles are (at least) restored in a period of about 10 to the 6th yr. PAHs are destroyed on time-scales of less than about 100,000 yr unless the oxidation efficiency is very small (about 0.001). Expected oxidation efficiencies of 0.1 would support the view that HAC mantles on grains in diffuse clouds can be restored in the intervals (about 10 to the 6th yr) between periodic low-velocity shocks, that PAHs are postshock transients, and that chemistry in diffuse clouds is significantly affected by the gas-grain interaction.

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