Chemical Reactions in CF₂Cl₂/Water (Ice) Films Induced by X-ray Radiation

Abstract

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.

Electron-driven chemistry of halogenated compounds in condensed phases: Effects of solvent matrices on reaction dynamics and kinetics

“…The experiments that are the focus of this article were carried out in three different ultrahigh vacuum (UHV) systems [36][37][38][39][40][41]. Figure 1 represents the schematic of a virtual (generalized) set-up that illustrates the instrumentation used in these chambers for characterization of the surface structure, composition and reactivity of thin films containing halogenated compounds.…”

“…The ESDIAD detector is used to measure angular distributions of desorbed positive and negative ions, and has TOF capability for mass-resolved ion detection. The details of these techniques have been reported elsewhere [36,40,41].…”

Cosmic-ray-driven electron-induced reactions of halogenated molecules adsorbed on ice surfaces: Implications for atmospheric ozone depletion and global climate change

“…There are also other studies of electron induced reactions of condensed CF identified by RAIRS (C-Cl) and (C-F) peaks, respectively [101,102]. For instance, about 10% of CF 2 Cl 2 remained on the surface with extended exposure of the X-ray source by 500 min [102].…”

“…For instance, about 10% of CF 2 Cl 2 remained on the surface with extended exposure of the X-ray source by 500 min [102]. The secondary electron current generated such a X-ray source is typically in the order of [101] stated that "the same chemical transformations (reaction products) were observed for CCl 4 /H 2 O (ice) films using the X-ray source or the electron gun in the absence or presence of an applied bias voltage (+200)".…”

Synchrotron x-ray photoemission study of soft x-ray processed ultrathin glycine-water ice films

“…[1][2][3][4][5] The understanding of these processes is of importance in various fields including astrochemistry, 6, 7 atmospheric chemistry, 8 and radiobiology. 9 Among the organic/water systems, low temperature water films containing amino acids, i.e., the simplest biologically active molecules and building blocks of proteins, are of particular interest.…”