Synthesis of complex molecules in dense interstellar clouds via gas-phase chemistry: A pseudo time-dependent calculation
A detailed model for the gas-phase chemistry of dense interstellar clouds is presented which includes, for the first time, reactions that both produce and destroy a representative sample of complex molecular species. In the model, which includes 200 species and over 1800 gas-phase reactions, an initial set of atomic and molecular abundances is allowed to evolve under constant physical conditions and in the absence of photodissociations. Our results indicate that, under these conditions, complex molecular species can be produced via gas-phase chemistry at abundances near observed valus but typically at times before steady state is reached and that their abundances attain a maximum value at times somewhat after the atomic carbon (C I) abundance peaks and begins to decrease. Since the steady-state abundances of most complex molecules are calculated to be significantly lower than observed values, it is concluded that although high gas density, low temperature, and shielding from ultraviolet radiation provide favorable environment for the synthesis of complex molecules, under nonequilibrium conditions significant production of complex molecules occurs only when the C I abundance is high and when the (C)/(CO) ratio is of order unity. The observational implications are discussed. No firm conclusion about cloud lifetimes can be drawn from this model until the time dependence of physical conditions is also treated. Finally, our results are compared with observations in the molecular clouds TMC-1, Orion (ridge), and Sgr B2.
- Research Organization:
- Department of Physics, Rensselaer Polytechnic Institute
- OSTI ID:
- 6125444
- Journal Information:
- Astrophys. J., Suppl. Ser.; (United States), Vol. 56:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMIC GASES
COSMOCHEMISTRY
MOLECULES
SYNTHESIS
ABUNDANCE
CARBON
CARBON MONOXIDE
CHEMICAL COMPOSITION
CHEMICAL REACTIONS
COSMIC DUST
INTERSTELLAR SPACE
MATHEMATICAL MODELS
QUANTITY RATIO
STEADY-STATE CONDITIONS
TABLES
TEMPERATURE DEPENDENCE
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMISTRY
DUSTS
ELEMENTS
FLUIDS
GASES
NONMETALS
OXIDES
OXYGEN COMPOUNDS
SPACE
640305* - Atomic
Molecular & Chemical Physics- Atomic & Molecular Theory- (-1987)