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UV radiation field inside dense clouds - Its possible existence and chemical implications
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1983
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Interstellar UV radiation cannot penetrate dense clouds, so cosmic ray ionization is usually considered the sole driver of gas‑phase chemistry, though cosmic rays also cause electronic excitation of the gas. The study investigates whether UV photons produced by cosmic‑ray excitation of molecular hydrogen can sustain a chemically effective UV flux inside dense clouds. The authors model Lyman and Werner band photons of H₂ and assess their impact on carbon and CO chemistry. They find that a significant UV photon flux can exist inside dense clouds, enabling CO photodissociation to regenerate C I at a rate an order of magnitude faster than the CO + He⁺ reaction. Published in ApJ, April 1983 (DOI 10.1086/160896).
view Abstract Citations (476) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS UV radiation field inside dense clouds - Its possible existence and chemical implications Prasad, S. S. ; Tarafdar, S. P. Abstract Interstellar UV radiation cannot penetrate into the interior of dense clouds, and cosmic ray ionization is thought to be the sole driver of the gas phase chemistry. However, cosmic ray energy deposition also involves electronic excitation of the absorbing gas. It appears, therefore, possible that emissions resulting from these excitations might maintain a significant flux of chemically effective UV photons in the interior of dense clouds. The present investigation is concerned with this possibility, taking into account a simplified approach. This approach involves a consideration of Lyman and Werner band photons of molecular hydrogen and their relevance to C and CO chemistry. The results of this investigation suggest that a chemically significant flux of UV photons may exist inside dense clouds due to cosmic ray excitation of the various band systems of hydrogen. These photons would recover C I from the CO reservoir in dense clouds via photodissociation at an order of magnitude faster rate than that possible in connection with the reaction of CO with He(+). Publication: The Astrophysical Journal Pub Date: April 1983 DOI: 10.1086/160896 Bibcode: 1983ApJ...267..603P Keywords: Hydrogen Clouds; Interstellar Matter; Molecular Clouds; Radiative Transfer; Ultraviolet Radiation; Carbon Monoxide; Cosmic Rays; Interstellar Chemistry; Molecular Excitation; Photodissociation; Astrophysics full text sources ADS |