Lifetime of molecules in a dark cloud model.
Abstract
The photodissociation lifetime of molecules in dark clouds is reanalyzed using a simple model of a spherical homogeneous dust cloud, the albedo values of Lillie and Witt (1976), and certain assumptions concerning the behavior of albedo down to the Lyman limit. The opacity resulting from abundant neutral atoms and molecules, particularly neutral carbon, is included in the analysis. The photodissociation lifetimes are computed as a function of cloud thickness up to a visual cloud thickness of 8 magnitudes for the molecules CO, OH, CH, H2CO, and NH3. Other processes which affect the lifetimes of these molecules are also considered. In particular, gas-phase chemical reactions which may limit the molecular lifetime in dense clouds are studied for homogeneous dust clouds with a visual extinction of 8 magnitudes and a density of 6500 per cu cm. It is found that with the exception of CO the molecules in typical dark clouds are destroyed predominantly by UV photodissociation.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 1978
- Bibcode:
- 1978A&A....69...85S
- Keywords:
-
- Astronomical Models;
- Interstellar Chemistry;
- Interstellar Matter;
- Molecular Gases;
- Nebulae;
- Albedo;
- Ammonia;
- Carbon Monoxide;
- Formaldehyde;
- Hydroxyl Radicals;
- Photodissociation;
- Transmissivity;
- Astrophysics;
- Dark Clouds:Dust;
- Dark Clouds:Molecules