Surface Chemistry and Radiation Chemistry of Trifluoroiodomethane (CF₃I) on Mo(110)

Abstract

The surface-induced and electron-induced chemistry of trifluoroiodomethane (CF3I), a potential replacement for chlorofluorocarbons (CFCs) and chlorofluorobromocarbons (halons), were investigated under ultrahigh vacuum conditions (p ∼ 1 × 10-10 Torr) on Mo(110). Results of temperature-programmed desorption (TPD) experiments indicate that dissociative adsorption of CF3I leads only to nonselective decomposition on Mo(110), in contrast to reactions of CF3I on other metal surfaces. Desorption of CF3 radicals and atomic iodine was detected mass spectrometrically during low-energy (10−100 eV) electron irradiation of four monolayer thick films of CF3I condensed at 100 K. Results of postirradiation temperature-programmed desorption experiments were used to identify CF2I2, C2F5I, C2F6, C2F4I2, and CFI3 as electron-induced reaction products of CF3I. Except for CFI3, all of these electron-induced reaction products of CF3I have been previously identified in γ-radiolysis studies, supporting our earlier claim that temperature-programmed desorption experiments conducted following low-energy electron irradiation of multilayer thin films provide an effective method to investigate the effects of high-energy radiation, including radical−radical reactions.

The role of low-energy electrons in the high-energy radiolysis of condensed CF3I

“…Previous γ -radiolysis studies have identified C 2 F 6 as a radiolysis product of CF 3 I [17,18]; in addition, C 2 F 6 has been reported to desorb from condensed CF 3 I on Ni(100) following irradiation with electrons of various energies below 100 eV [19]. The desorption peaks observed at ∼120 K (data not shown) for m/z 100 (C 2 F + 4 ) and 119 (C 2 F + 5 ) were assigned to C 2 F 6 , as in our previous experiments [16].…”

“…The results of a post-irradiation temperature-programmed desorption experiment conducted following 4 eV electron irradiation of a 13 ML thin film of condensed CF 3 I are shown in figure 2(B). Only the three mass spectral fragments that evinced desorption peaks were monitored in this particular experiment in order to increase the signal-to-noise ratio and to clearly demonstrate the identification of the two radiolysis products C 2 F 3 I and C 2 F 3 I 3 , both of which we failed to identify in our previous work involving 55 eV electron irradiation [16]. Although an extensive search of mass spectral fragments was not performed at incident electron energies above 4 eV, all seven radiolysis products were also observed following high-energy (500 eV) electron irradiation of condensed CF 3 I (figure 2(C)).…”

“…Because reaction (1) is generally characterized by remarkably high cross sections, especially near 0 eV, DEA is expected to play a prominent role in the high-energy radiolysis of halogenated molecules. As part of a series of postirradiation studies involving halogenated molecules [6][7][8][9][10], we have chosen to investigate the role of dissociative electron attachment in the condensed phase radiolysis of a simple halocarbon, CF 3 I.…”

Low-Energy Electron-Induced Oligomerization of Condensed Carbon Tetrachloride

“…The identification of short- and long-chain halocarbons with two, three, four, five, and six or more carbon atoms demonstrates the low-energy electron-induced oligomerization of condensed CCl 4 . Previous studies have detected low-energy electron-induced carbon−carbon coupling and identified two- 40,52,53 and three-carbon 36 species following low-energy electron irradiation of CH 3 OH, CF 3 I, CF 2 Cl 2 , and CCl 4 . (In comparison to ref , we speculate that our experiments included a more exhaustive search of mass spectral fragments.)…”

Thermal decomposition and fire‐extinguishing mechanism of CF3I: A combined theoretical and experimental study

“…CF 3 I is a new environmentally friendly refrigerant and insulating gas, featuring a low GWP below 5 and an ODP as low as 0.008 [12, 13], Its atmospheric life is only 1.825 days and has little impact on the environment. In addition, CF 3 I is colorless, tasteless, non‐conductive, inflammable and no residue will be left after the fast fire‐extinguishing process [14, 15], and the relevant toxicity studies show that CF 3 I has a very low cardiac sensitization lowest observable adverse effect level, with a volume fraction of 0.4%, and its median lethal concentration (LC 50 ) to Sprague Dawley rats is ~27.4% [16], which is much higher than its MEC. Besides, the standard of the American Compressed Gas Association divides CF 3 I into nontoxic gases [17].…”