NONEQUILIBRIUM CHEMISTRY IN SPACE

Chemical processes by accelerated species do not proceed in thermal equilibrium with the target molecules. The hot or suprathermal reactions are characterized by the fact that a kinetic energy ranging from about 1 to few 10 eV is imparted to the collision complex. Reaction rates are by orders of magnitude higher and products are more diversified than in classic thermally controlled reactions. Space is rich in energetic atoms, ions, molecules, fragments, clusters, and grains from cosmic rays, solar or stellar radiation, shock waves and many secondary acceleration processes with energies ranging from a few eV (photodissociation) to some TeV (cosmic rays). Non-equilibrium chemistry is, thus, typical for space. Suprathermal reactions in the solid state can effectively compete with radiolysis or photolysis and ion molecule interactions, particularly in view of the formation of complex organic matter by multicenter reactions in the collision cascades.