MOLECULAR GAS

The largest gas clouds (10,000 times the mass of the Sun) form GIANT MOLECULAR CLOUDS.

In their denses cores, dust blocks harmful UV light from other stars, and the cloud becomes very cold. Such conditions are ideal to bond atoms into molecules.

Several molecular building processes occur:

• H atoms stick to dust grains and eventually bond to form molecular hydrogen, H₂.
• In very dense environments, atoms (ions) can gently collide to bond into molecules.
• Shock heating of gas provides another means for molecule formation.

Many molecules emit radio energy though rotational and vibrational transitions, so that astronomers can study the chemistry of distant clouds. We find simple and complex molecules are present formed mainly from hydrogen (H), carbon (C), oxygen (O), and nitrogen (N).

CO - carbon monoxide
H₂O - water vapor
CH₃CH₂OH - ethyl alcohol
PAHs - polycyclic aromatic hydrocarbons (rows of C rings)