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| Paper: |
The chemistry of the diffuse interstellar gas |
| Volume: |
12, The Evolution of the Interstellar Medium |
| Page: |
207 |
| Authors: |
van Dishoeck, Ewine F. |
| Abstract: |
Recent observations are examined in the discussion of the diffuse high-latitude clouds and compared to theoretical models of the diffuse interstellar gas. The temperature and density structure of the clouds are examined, and contributions to the abundances of species is assessed for quiescent steady-state reactions, shock-heated chemistry, and grain-surface chemistry. Models of the clouds are evaluated by comparing data from observations of lines of H2, molecules such as CO and CN, and radicals such as CH and OH. The densities of the diffuse clouds are approximately a few hundred/cu cm, and the temperatures range from 25 to 40 K in the centers and 100 to 150 K at the edges. The array of observed species cannot be reproduced by the current shock models, and diagnostics for studying the origin and evolution are found to be rare. |
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