Heterogeneous reactions, involving the interaction of gas-phase molecules with the surfaces of dust grains, are the primary mechanism for the formation of molecular species on dust grains in the interstellar medium.

Radical-radical reactions, involving the combination or disproportionation of free radicals, are the dominant type of surface reaction on dust grains in the interstellar medium.

Hydrogen atoms play multiple roles in surface chemistry on dust grains: they act as catalysts for surface reactions, terminate radical chains, and promote the formation of molecular hydrogen.

Water, carbon monoxide, ammonia, and methanol are all commonly observed as products of surface chemistry on dust grains.

The composition of the dust grain, including the presence of specific elements and functional groups, is the primary factor that determines its reactivity.

The effect of temperature on the rate of surface reactions depends on the specific reaction and the activation energy required.

Defects on the surface of a dust grain can act as active sites for surface reactions, providing specific locations where molecules can interact and react.

Vacancies, interstitials, dislocations, and grain boundaries are all common types of defects found on the surface of dust grains.

Larger dust grains have more surface area available for reactions, potentially leading to higher rates of surface chemistry.

Cosmic rays can generate free radicals, induce desorption of molecules, and cause structural changes in dust grains, all of which can influence surface chemistry.

The composition of the gas-phase surrounding a dust grain influences the types of molecules that can interact with the surface, the rate of surface reactions, and the types of products formed.

Increasing temperature generally increases the rate of desorption of molecules from a dust grain surface.

The sticking coefficient of a molecule on a dust grain surface can be influenced by the temperature of the dust grain, the composition of the dust grain, and the energy of the incoming molecule.

Surface diffusion allows molecules to move across the dust grain surface, facilitating their encounter and promoting the formation of molecular complexes.

The presence of ice on a dust grain surface can provide a medium for reactions to occur, inhibit the mobility of molecules on the surface, and alter the composition of the surface.