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Summary

Molecular clouds contain gas at T ∼ 15 K and at densities of n ∼ 100 cm^-−3 and upward. Although $H_{2}$ provides the overwhelming majority of molecules in a molecular cloud, the absence of an electric dipole in the symmetric $H_{2}$ molecule means it is difficult to observe. The 2.6 mm emission from the $J = 1 \to 0$ rotational transition in $^{12} CO$ is among the most useful ways to observe molecular gas. Most molecular clouds, however, are optically thick to the 2.6 mm emission from $^{12} CO$ ; seeing to their centers requires observing the scarcer isotopologue $^{13} CO$ rather than the more abundant $^{12} CO$ . Within dusty, optically thick molecular clouds, molecules are made by dust grain catalysis. In the surface layers of molecular clouds, molecules are destroyed through photodissociation by ultraviolet light. However, molecular clouds are self-shielded from UV outside the cloud.

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7 - Molecular Clouds

Summary

Gas-phase UV cross sections of radicals

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2 results

7 - Molecular Clouds

Summary

Gas-phase UV cross sections of radicals