Reactivity and structure of CF3I on Ru(001)
A variety of surface-sensitive techniques are used to elucidate the reaction pathways, as well as adsorbate structures, associated with thermal activation of CF{sub 3}J following adsorption on Ru(001) at 100 K. XPS shows that the C-I bond of CF{sub 3}I dissociates below 200 K to form CF{sub 3}(ad) and I(ad); the subsequent reactions of CF{sub 2} are best viewed as being regulated by the availability of surface sites. CF{sub 3}(ad) dissociates to CF{sub 2}(ad) below 200 K. Further CF{sub 3} dissociation, some of which is activated by H(ad), occurs between 200 and 400 K until all available sites are filled. Desorption of the remaining CF{sub 3}, peaking at 705 K, once again opens surface sites for decomposition. This is followed by recombination of the products to form CF{sub 3}(g). No evidence for CF(ad) is ever observed. Hydrogen coadsorption studies explain interesting features associated with fluorine evolution. HREELS and ESDIAD results indicate that CF{sub 3} adopts a tilted configuration on Ru(001). 53 refs., 11 figs., 3 tabs.
Thermally stimulated desorption of neutral CF3 from CF3I on Ag(111)
The low temperature thermal chemistry of CF3I on Ag (111) presents an example of competing reaction pathways; molecular desorption vs desorption of radical CF3. Temperature programmed desorption and angle resolved temperature programmed desorption, complemented with Auger electron spectroscopy and low energy electron diffraction, were used to discern the mechanism of the CF3 radical desorption channel. CF3 desorption is limited to the first monolayer of CF3I; 0.75 ML CF3I is the coverage used for angular dependence measurements. At 90 K most of the CF3I adsorbs molecularly to the metal, but also present under these conditions are dissociative adsorption and thermal decomposition channels limited to C–I bond cleavage. The decomposition product, CF3, desorbs as a radical at high temperatures (∼320 K) with the I remaining on the surface until 850 K. At submonolayer CF3I coverages, thermal activation produces a low temperature (100–150 K) radical desorption channel. Results indicate that low temperature CF3 t...
Coordination chemistry of metal surfaces: Chemisorption of PF3
The electronic and thermal properties of PF3 bonded to surfaces of Cr, Fe, Ni, Cu, Ru, Pd, Ir, and Pt were investigated by means of ultraviolet photoelectron spectroscopy (UPS), electron energy loss sectroscopy, LEED, and thermal desorption. Bond formation can be described in terms of coupling of the highest occupied ligand orbital (σ‐donor 8a1) to metallic s states and of ’’back donation’’ of metallic d electrons into the lowest empty ligand orbital (π‐acceptor 7e). The observed lowering of the ionization potential of the 8a1 level exhibits close similarities with the properties of the corresponding zero‐valent mononuclear complex compounds, indicating that in this case the chemisorption bond has to be considered as an essentially local phenomenon. The agreement is best with the fcc metals Ni, Pd, Ir, and Pt, whereas larger variations (as well as a dependence on the crystallographic orientation of the surface) were found with the bcc metals Cr and Fe. Ordered 2×2 overlayers observed with Ni(111) and Pd(1...