Electron-Stimulated Chemical Reactions in Carbon Tetrachloride/Water (Ice) Films

Abstract

The electron-stimulated chemical reactions in carbon tetrachloride/water (ice) and ice films have been studied using reflection-absorption infrared spectroscopy (RAIRS) and mass spectrometry. CO 2 , CO, and HCl were identified as the final neutral reaction products in the electron-stimulated degradation of CCl 4 , while COCl 2 and C 2 Cl 4 were produced as intermediates. Molecular H 2 and O 2 were detected as neutral gas-phase products in the electron beam irradiation of pure ice films. Production of molecular oxygen was, however, efficiently quenched during irradiation of CCl 4 /H 2 O(ice) mixtures. A reaction mechanism is postulated based on the reactivity of the trichloromethyl ( • CCl 3 ) radical and dichlorocarbene (:CCl 2 ) intermediates. Reactions between the trichloromethyl ( • CCl 3 ) radical and oxygen or hydroxyl radicals lead to the production of phosgene, the subsequent electron-stimulated decomposition of which produces CO or CO 2 . In contrast, reactions involving dichlorocarbene produce CO via hydrolysis or C 2 Cl 4 as a result of a carbon-carbon coupling reaction.

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

“…The CO 2 , COCl 2 , H 3 O þ and H x D 3 À x O þ intensities grow to maxima and then decrease upon prolonged electron irradiation. This growth and decrease of the carbon-containing products COCl 2 and CO 2 upon electron irradiation is qualitatively similar to that seen for CCl 4 /water films [39]. Negative absorption peaks observed between 3600-3000 and 920-730 cm À1 are due to the electron-stimulated consumption of both H 2 O and CDCl 3 .…”

“…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.…”

High dose radiolysis of aqueous solutions of chloromethanes: Importance in the storage of radioactive organic wastes

“…An unsaturated compound is a good radical trap and may act as a seed for the initiation of polymer formation with any other carbon centered radical. Carbene radicals are reported to be an intermediate product in CCl 4 -water (ice) films [35] and in heme/TiO 2 [36], but their existence in aqueous solutions is unknown. Other oxygen containing products like HCHO, HCOOH, CO and CO 2 are also reported in the radiolysis of chloromethanes [8,9,13].…”

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)".…”