The effect of X-ray irradiation on the chemical and physical properties of a semifluorinated self-assembled monolayer (CF-SAM) derived from 1H,1H,2H,2H-perfluorodecanethiol (CF3(CF2)7(CH2)2SH) adsorbed on gold and copper substrates was studied using X-ray photoelectron spectroscopy. During the initial period of irradiation, the effects of electron-stimulated C-F, C-C, and S-X (X ) Au, Cu) bond breaking are responsible for changes in the chemical composition of the CF-SAM. Furthermore, the evolution of the C(1s) X-ray photoelectron spectral region indicates that C-F rather than C-C bond cleavage dominates desorption within the CF-SAM. Except for fluorine desorption, irradiation-induced changes to the chemical and structural properties of the CF-SAM were most pronounced during the initial stages of irradiation, prior to the development of a highly cross-linked carbonaceous overlayer. X-ray irradiation of CF-SAMs adsorbed on Au also resulted in the production of new irradiation-induced sulfur species. A comparison with experiments carried out on a n-hexanedecanethiol (CH3(CH2)15SH)-based SAM revealed that the concentration and distribution of these irradiation-induced sulfur species were both sensitive to the SAM's initial chemical composition. On Cu substrates, native CF-SAMs formed an effective barrier to oxygen diffusion although the film's permeability to oxygen increased for CF-SAMs pre-exposed to X-ray irradiation.

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.