The chemical evolution of molecular clouds

Abstract

view Abstract Citations (149) References (53) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The chemical evolution of molecular clouds. Iglesias, E. Abstract The 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. Publication: The Astrophysical Journal Pub Date: December 1977 DOI: 10.1086/155727 Bibcode: 1977ApJ...218..697I Keywords: Chemical Evolution; Cloud Physics; Interstellar Chemistry; Interstellar Gas; Molecular Spectra; Chemical Equilibrium; Interstellar Matter; Organic Compounds; Astrophysics full text sources ADS |