A Model for Ion Bombardment-Induced Organic Synthesis on Carbon-Bearing Surfaces in Cosmic Space

The role of irradiation of carbon-bearing grains by energetic particles in formation and evolution of organic matter in the interstellar medium and Solar System is studied. Experimental evidence for the possibility of the organic synthesis directly from inorganic reactants by keV ion bombardment is presented. Irradiation of graphite powder containing hydrogen by He + and N + as well as by H + ions at room temperature was found to produce polycyclic aromatic hydrocarbons (PAHs), known to be among the most abundant organic molecules in meteorites as well as in the interstellar medium. Qualitative and quantitative analysis of the PAHs obtained was performed and PAH emergence was shown to be due to the irradiation for both types of ions. Radiation-induced PAH formation may occur on the surfaces of carbon grains in the circumstellar regions and on the regolith particles of carbon-bearing atmosphereless celestial bodies of the Solar System, the wind from the nearest star being the source of hydrogen and energy to form C-H bonds. This mechanism of PAH formation has been shown to be able to explain the amount of PAHs observed in the interstellar medium.