Oxide Surface Photoreaction Dynamics and Thermal Chemistry

1. Totir, G. G.; Le, Y.; Osgood, R. M., Jr. Photoinduced-Reaction Dynamics of Halogenated Alkanes on Iron Oxide Surfaces: CH3I on Fe3O4(111)-(2´2). Journal of Physical Chemistry B (2005), 109(17), 8452-8461.
The adsorption, thermal chemistry and photoreaction dynamics of methyl iodide on the (2×2) 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 (2×2) surface at 100 K, 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 eV and 0.3 eV CH3 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 ~0° 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 CH3I is normal to the crystal plane.
  • TPD (coverage-dependence)
  • TOF-QMS (angular-dependence) submonolayer coverage>1 ML coverage

 

 

 

2. Le, Y.; Totir, G. G.; Osgood, R. M., Jr. Chloromethane Surface Chemistry on Fe3O4(111)-(2×2): a Thermal Desorption Comparison of CCl4, CBr2Cl2, and CH2Cl2. (in revision)
The surface chemistry of CBr2Cl2 and CH2Cl2 on the Fe3O4(111)-(2×2) selvedge of single-crystal a-Fe2O3 (0001) has been investigated using temperature programmed reaction and desorption (TPR/D) measurements. The TPR/D spectra show that dissociative formation of CCl2 followed by its reaction with lattice oxygen is central to the monolayer reaction chemistry in chloromethanes. The specific branching ratios of the various desorbed products are compared among with those obtained from CCl4, CBr2Cl2, and CH2Cl2 on the (2×2) surface.
  • TPD of CCl4

 

 

  • TPD of CBr2Cl2

 

 

  • TPD of CH2Cl2

 

 

Contact Interface in Molecular Electronics and Optics
  1. TPD of (CH3)3SiCHN2 on Ru(0001) (project in progress)