Energy- and Angle-Resolved Fragmentation of Ethyl Bromide on GaAs(110)

Photoinduced-Reaction Dynamics of Halogenated Alkanes on Iron Oxide Surfaces: CH3I on Fe3O4(111)−(2×2)

The adsorption, thermal chemistry, and photoreaction dynamics of methyl iodide on the (2x2) magnetite termination of natural single-crystal hematite have been investigated by time-of-flight quadrupole mass spectrometry (TOF-QMS), temperature-programmed desorption (TPD) and Auger electron spectroscopy (AES). The methyl iodide thermal desorption spectra, taken after dosing the (2x2) surface at 100 K with CH(3)I, show a multiple-peak coverage-dependent behavior, consistent with the presence of several distinct adsorbed phases, along with defect-mediated dissociative chemisorption in the first monolayer. At >1 ML, methyl iodide forms a metastable physisorbed second layer, which desorbs at 148 K, but at higher coverage converts to a layer, which desorbs at 170 K. In the presence of low-fluence-pulse irradiation at 248 nm, angle-resolved TOF-QMS measurements show that 1.6 and 0.3 eV CH(3) fragments are ejected from the adsorbate surface; these fragments originate from direct photodissociation and dissociative photoinduced electron transfer, respectively. These energetic photoejected fragments have characteristic angular distributions peaked at approximately 0 degree with respect to the surface normal. These results and the coverage-dependent relative intensities suggest that the predominant orientation in the first monolayer of the adsorbed CH(3)I is normal to the crystal plane.

Surface-reconstruction-switched adsorbate photofragmentation dynamics

Energy-resolved angular distributions of neutral fragments ejected during photoinduced electron transfer reaction of CH3Br on GaAs(100) exhibit three distinct methyl-radical ejection channels. These undergo marked changes when the termination is switched from the Ga-rich c(8 x 2) to the As-rich c(2 x 8). Our observations are consistent with a strong adsorption-site dependence of the dynamics.