Photodissociation of the group VIB (Cr,Mo,W) hexacarbonyls has been studied at 248 nm using molecular beam photofragment spectroscopy. One, two and three photon processes have been observed. Analysis of the product velocity distributions shows that the photodissociation mechanism consists of sequential CO eliminations with the nth photon channel best described as the single photon photodissociation of the stable products of the n-1st photon channel. The product translational energy distribution for the first CO elimination step is quantitatively similar for all three hexacarbonyls and characteristic of a repulsive translational energy release. The product translational energy distributions of all subsequent CO elimination steps are accurately described by a simple, microcanonical model. Qualitative molecular orbital considerations suggest that the large product translational energy observed in the first CO elimination step results from a repulsive σ interaction between the closed shell CO ligand and an excited molecular orbital which has a significant admixture of metal (n+1)pz, (n+1)s and ndz2 orbitals. This repulsive interaction is absent in the remaining CO elimination steps because there are vacancies in the coordination shell along the z axis.
A molecular beam study of the Cl2+GaAs(s) reaction has been performed for surface temperatures in the range of 300–550 K. The gas phase neutral reaction products are identified by mass spectroscopy using electron bombardment ionization. Detailed analysis of the surface temperature dependence of the mass spectrum of the observed reaction products indicates that only three neutral reaction products are formed in this temperature range: GaCl3, AsCl3, and As4. At low (high) surface temperatures, only AsCl3 (As4) is observed. The ratio of the etching rates of Ga and As is independent of the surface temperature and within the range expected for stoichiometric etching. The change in the mode of As removal with surface temperature for the incident Cl2 flux implies that surface diffusion is important at surface temperatures above 400 K.
Pure TiO 2 and different concentrations of Cu-doped TiO 2 with anatase/rutile/brookite triphasic structure were successfully synthesized through a simple hydrothermal process and characterized by X-ray diffraction (XRD), Raman, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectra (XPS), diffuse re ectance spectra (DRS), photoluminescence spectra (PL) and Brunauer-Emmett-Teller surface area (BET). Both pure and Cu-doped TiO 2 show relatively high photocatalytic activity owing to their considerable surface areas. Moreover, the three-phase coexisting structure and the conversion between Cu 2+ and Cu + ions facilitate the separation of photogenerated electrons and holes, which is favorable for photocatalytic performance. 1%Cu-TiO 2 exhibits the highest photocatalytic activity and the degradation degree of rhodamine B (RhB) reaches 93.5% after 30 min, which is higher than that of monophasic/biphasic 1%Cu-TiO 2 . •O 2 − radical is the main active specie, and h + and •OH are subsidiary in the degradation process.
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