Chemical Reactions in CFCl/Water (Ice) Films Induced by X-ray Radiation

The chemical reactions initiated by high-energy radiation (Mg or Al K X-rays) in amorphous CFCl/H O(ice) films have been studied using a combination of reflection absorption infrared spectroscopy (RAIRS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Following deposition, the structure of the CFCl/HO(ice) film resembles an amorphous ice phase having CFCl molecules caged within the film, and a smaller number of CFCl molecules adsorbed on the ice surface. X-ray irradiation produces a broad distribution of low-energy secondary electrons whose interactions with CF Cl/HO(ice) films are associated with the production of HO, CO, and COF (carbonyl fluoride) as detected by RAIRS. COF is identified as an intermediate species whose electron-stimulated decomposition leads to CO production. The product partitioning is dependent on the film's initial composition; in water rich films, CO and COF production is favored, whereas a more thermally stable, partially halogenated polymeric CFCl film is detected by XPS in CF Cl rich films. Chloride and fluoride anions are also produced and solvated (trapped) within the ice film. During the early stages of X-ray irradiation, the dominance of Cl anions formed in the film by reaction with low-energy secondary electrons is consistent with the suggestion that C-Cl bond cleavage of CFCl via dissociative electron attachment (CFCl + e → ·CFCl + Cl) is the dominant initial process.