Surface Reactions

Adsorption

Atoms and molecules from the gas phase stick to the surface of dust grains. This is the first step in many surface reactions.

• Example: H atoms sticking to dust grains.

Note

Inclure la video (Leiden)

Hydrogenation

Hydrogen atoms on the surface of dust grains can add to other atoms or molecules, leading to the formation of more complex species.

• Example:

\[ \text{CO} + \text{H} \rightarrow \text{HCO} \rightarrow \text{H}_2\text{CO} \rightarrow \text{CH}_3\text{OH} \]

Chemical Reactions on Dust Grain Surfaces

Once adsorbed, atoms and molecules can react with each other on the dust grain surfaces, forming more complex molecules.

• Example:

Formation of water ice through

\[ \text{H} + \text{O} \rightarrow \text{OH}\) followed by \(\text{OH} + \text{H} \rightarrow \text{H}_2\text{O} \]

Desorption

Molecules formed on the dust grains can be released back into the gas phase, typically through processes like thermal desorption, photodesorption, or cosmic-ray-induced desorption.