Matrix isolation model studies on the radiation-induced transformations of small molecules of astrochemical and atmospheric interest

Abstract The radiation-induced transformations of small molecules at low temperatures play an important role in the interstellar, planetary and atmospheric chemistry. This work presents a review of our recent model studies on the radiation chemistry of relevant molecules in solid noble gas (Ng) matrices, including some preliminary new results. Among the triatomic molecules, water and carbon dioxide were studied in detail. The radiation-induced degradation of isolated H 2 O yields hydrogen atoms and OH radicals, while oxygen atoms are produced at higher doses. Isolated CO 2 molecules are decomposed to yield CO and trapped oxygen atoms. Upon annealing the trapped O and H atoms are mobilized selectively at different temperatures and react with other trapped species. The formation of HCO and HOCO radicals was observed in the mixed H 2 O/CO 2 /Ng systems. Other studies were concerned with the radiation-induced degradation of simple organic molecules (methanol, formic acid) and chlorofluorocarbons (CFCl 3 , CF 2 Cl 2 ). Preliminary results for methanol revealed deep dehydrogenation yielding HCO and CO, whereas CO 2 , CO and HOCO were detected as primary products for formic acid. In the case of chlorofluorocarbons, significance of ionic channels was demonstrated. The implications of the results for modeling the processes in astrochemical ices and atmosphere are discussed.