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The chemical reactions initiated by high-energy radiation (Mg or Al K R X-rays) in amorphous CF 2 Cl 2 /H 2 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 CF 2 Cl 2 /H 2 O(ice) film resembles an amorphous ice phase having CF 2 Cl 2 molecules caged within the film, and a smaller number of CF 2 Cl 2 molecules adsorbed on the ice surface. X-ray irradiation produces a broad distribution of low-energy secondary electrons whose interactions with CF 2 Cl 2 /H 2 O(ice) films are associated with the production of H 3 O + , CO 2 , and COF 2 (carbonyl fluoride) as detected by RAIRS. COF 2 is identified as an intermediate species whose electron-stimulated decomposition leads to CO 2 production. The product partitioning is dependent on the film's initial composition; in water rich films, CO 2 and COF 2 production is favored, whereas a more thermally stable, partially halogenated polymeric CF x Cl y film is detected by XPS in CF 2 Cl 2 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 Clanions formed in the film by reaction with low-energy secondary electrons is consistent with the suggestion that C-Cl bond cleavage of CF 2 Cl 2 via dissociative electron attachment (CF 2 Cl 2 + ef ‚CF 2 Cl + Cl -) is the dominant initial process.

The kinetics of decomposition and subsequent chemistry of adsorbed CF(2)Cl(2), activated by low-energy electron irradiation, have been examined and compared with CCl(4). These molecules have been adsorbed alone and coadsorbed with water ice films of different thicknesses on metal surfaces (Ru; Au) at low temperatures (25 K; 100 K). The studies have been performed with temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), and x-ray photoelectron spectroscopy (XPS). TPD data reveal the efficient decomposition of both halocarbon molecules under electron bombardment, which proceeds via dissociative electron attachment (DEA) of low-energy secondary electrons. The rates of CF(2)Cl(2) and CCl(4) dissociation increase in an H(2)O (D(2)O) environment (2-3x), but the increase is smaller than that reported in recent literature. The highest initial cross sections for halocarbon decomposition coadsorbed with H(2)O, using 180 eV incident electrons, are measured (using TPD) to be 1.0+/-0.2 x 10(-15) cm(2) for CF(2)Cl(2) and 2.5+/-0.2 x 10(-15) cm(2) for CCl(4). RAIRS and XPS studies confirm the decomposition of halocarbon molecules codeposited with water molecules, and provide insights into the irradiation products. Electron-induced generation of Cl(-) and F(-) anions in the halocarbon/water films and production of H(3)O(+), CO(2), and intermediate compounds COF(2) (for CF(2)Cl(2)) and COCl(2), C(2)Cl(4) (for CCl(4)) under electron irradiation have been detected using XPS, TPD, and RAIRS. The products and the decomposition kinetics are similar to those observed in our recent experiments involving x-ray photons as the source of ionizing irradiation.