| Term: | Diffuse interstellar clouds |
| Definition: |
An interstellar cloud in which hydrogen is completely dissociated and which is less dense and dusty than molecular clouds. In diffuse interstellar clouds photoabsorption of the background ultraviolet (UV) radiation field is an important dissociating and ionizing process. Typical densities and temperatures of diffuse clouds are 10^2 to 10^3 cm^-3 and 20 to 100 K respectively. Because of modest extinctions (≤ 1 mag), photodissociation processes are important in diffuse clouds preventing the formation of larger molecules. |