Kinetics of electron-induced decomposition of CF2Cl2 coadsorbed with water (ice): A comparison with CCl4

Abstract

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.

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

“…ACCEPTED MANUSCRIPT -29 -that were detected in the TPD measurements of CF 2 Cl 2 and CCl 4 [75,103]. In a general case, the TPD technique does not have the capability to distinguish the CF 2 Cl 2 (CCl 4 ) and its dissociation product CF 2 Cl (CCl 3 ) adsorbed on the surface.…”

Reaction dynamics following electron capture of chlorofluorocarbon adsorbed on water cluster: A direct density functional theory molecular dynamics study

“…Although many investigations for the molecules on ice have been carried out by several groups, the works for the electron capture dynamics are limited. [17][18][19] In particular, there is no theoretical work for the electron capture dynamics of halocarbon on ice.…”

Probing Molecular Solids with Low-Energy Ions

“…The properties, surface structure, and reactions of ice have been studied in significant detail because of their importance to several chemical and physical processes that occur at low temperatures (90,91), as well as their catalytic role in polar stratospheric clouds in the depletion of the ozone layer (1)(2)(3)92) and their relevance in chemistry in the interstellar medium (25,(93)(94)(95). Ice surfaces prepared at low temperatures offer a unique environment in which to investigate various chemical and physical processes, such as diffusion (21), cluster formation (40,41), phase transition (96,97), chemical reaction, hydrogen/deuterium exchange (98)(99)(100)(101)(102)(103)(104)(105)(106), interactions with small molecules (46), and adsorption (26,30). All these phenomena can be promoted and/or identified with hyperthermal energy (1-100-eV) ion collisions.…”

“…We can better understand the molecular details of processes taking place in such solids by using vibrational spectroscopy, which in conjunction with TPD is often an indispensable tool . Also, surface-sensitive tools, such as X-ray photoelectron spectroscopy (XPS), have been employed with TPD to study ice films (26,46). Ions whose energy ranges between 1 and 100 eV (47-71)-which is known as the hyperthermal energy regime and, especially with energies below 10 eV (9,72,73), constitutes the ultralow-energy regime-are novel probes for studies of new phenomena.…”