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The chemical evolution of molecular cloudsThe nonequilibrium chemistry of dense molecular clouds (10,000 to 1 million hydrogen molecules per cu cm) is studied in the framework of a model that includes the latest published chemical data and most of the recent theoretical advances. In this model the only important external source of ionization is assumed to be high-energy cosmic-ray bombardment; standard charge-transfer reactions are taken into account as well as reactions that transfer charge from molecular ions to trace-metal atoms. Schemes are proposed for the synthesis of such species as NCO, HNCO, and CN. The role played by adsorption and condensation of molecules on the surface of dust grains is investigated, and effects on the chemical evolution of a dense molecular cloud are considered which result from varying the total density or the elemental abundances and from assuming negligible or severe condensation of gaseous species on dust grains. It is shown that the chemical-equilibrium time scale is given approximately by the depletion times of oxygen and nitrogen when the condensation efficiency is negligible; that this time scale is probably in the range from 1 to 4 million years, depending on the elemental composition and initial conditions in the cloud; and that this time scale is insensitive to variations in the total density.
Document ID
19780034431
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Iglesias, E.
(Comision Nacional de Estudios Geoheliofisicos; Instituto de Astronomia y Fisica del Espacio, Buenos Aires, Argentina; California, University Berkeley, Calif., United States)
Date Acquired
August 9, 2013
Publication Date
December 15, 1977
Publication Information
Publication: Astrophysical Journal
Subject Category
Astrophysics
Accession Number
78A18340
Funding Number(s)
CONTRACT_GRANT: NSF AFT-75-02181
CONTRACT_GRANT: NGR-05-003-578
Distribution Limits
Public
Copyright
Other

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