Blake, Geoffrey A. and Keene, Jocelyn and Phillips, T. G. (1985) Chlorine in dense interstellar clouds - The abundance of HCl in OMC-1. Astrophysical Journal, 295 (2). pp. 501-506. ISSN 0004-637X http://resolver.caltech.edu/CaltechAUTHORS:20120910-114824466
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We report the first detection of a chlorine-bearing molecular species in the interstellar medium via emission from the J = 1 → 0 transition of HCl at 625.9 GHz toward OMC-1. The relative strengths, widths, and velocities of the resolved hyperfine components are consistent with moderate optical depth emission originating from dense, quiescent molecular cloud material (V_(LSR) = 9 km s^(-1)). The overall emission strength implies a fractional abundance of f(HCl/H_2) ~ (0.5-5.0) x 10^(-8), depending on the density of the emitting region. This is approximately an order of magnitude below previous theoretical estimates and a factor of 3-30 below the cosmic abundance of Cl. Recent laboratory work suggests that the lowered fractional abundance of HCl is caused by a combination of depletion onto grains with gas-phase loss processes such as the reaction of HCl with C^+.
|Additional Information:||© 1985 American Astronomical Society. Received 1984 December 19; accepted 1985 February 25. We would like to thank the crew of the Kuiper Airborne Observatory for their effective support of these observations; V. G. Anicich and W. T. Huntress, Jr., for helpful discussions about the chemistry of interstellar chlorine; and S. Green for providing the collisional excitation coefficients. This research has been supported by NASA grant NAG 2-1 to the California Institute of Technology.|
|Subject Keywords:||interstellar: molecules; molecular processes; abundance; astronomical spectroscopy; chlorine; emission spectra; hydrochloric acid; interstellar chemistry; interstellar gas; molecular clouds; optical thickness|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Aucoeur Ngo|
|Deposited On:||11 Sep 2012 20:24|
|Last Modified:||26 Dec 2012 16:08|
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