What is the name of the process by which molecules form in dense interstellar clouds?

Surface chemistry is responsible for molecular formation in dense interstellar clouds, where atoms and molecules adsorb onto cold dust grains and undergo reactions. Unlike gas-phase chemistry, which relies on high-energy collisions, surface reactions enable the formation of complex molecules at extremely low temperatures. Hydrogenation reactions, in which atomic hydrogen reacts with adsorbed species, contribute to the formation of molecules like water, methanol, and ammonia. Since these icy mantles eventually sublimate or become incorporated into comets, surface chemistry plays a crucial role in distributing organic compounds throughout the universe, influencing the chemical evolution of planetary systems.