Stabilisation of alkali-adsorbate-induced states on Cu(111) surfaces

The Li and Cs alkali-adsorbate-induced states on a model Cu(111) surface are studied theoretically using the coupled angular mode and the wave packet propagation methods. Their energy position and their decay rate via one-electron transfer into the metal are calculated. An unoccupied alkali-induced state is found with a rather long lifetime, much longer than those found in the case of free-electron metal surfaces. This is attributed to the combined effect of the hybridisation of the alkali levels and of the Cu(111) projected band gap along the normal to the surface that blocks the electron transfer between the adsorbate and the metal. This qualitatively explains the experimental finding of a long-lived state by Bauer et al. [Phys. Rev. B 55 (1997) 10 040] and Ogawa et al. [Phys. Rev. Lett. 82 (1999) 1931].     

Ion-exchange-induced formation of glassy electrooptical and nonlinear optical nanomaterial

Subsurface electrooptical glass-ceramic layers are formed in an alkaline-silica-niobate glass using ion exchange technique. Ways of selection of glass compositions and ion exchange conditions to form such layers are discussed. It is shown that there are two ways to form glass-ceramics; the first one is the glass ceramization during the ion exchange treatment at higher temperatures, and the second one is the glass ceramization in heat treatment of the samples ion exchanged at lower temperatures, at which glass crystallization does not take place. The latter allows producing glass-ceramics layers of controllable thickness, because in this case diffusion process strongly obeys Fick equation.     

Determination of the individual hydrocarbon composition of gasolines by the combination method. Communication 2. Two gasolines from Kazanbuiak petroleums

Russian Chemical Bulletin -     

Supported silica-molybdena catalysts for olefin metathesis activated by photoreduction

Cyclopropane (CP) or methylcyclopropane (MCP) chemisorption on silica-molybdena catalysts photoreduced in CO was found to result in a sharp increase (by one order of magnitude) of specific activities for olefin metathesis (propene, 1-hexene, ethyl oleate). IR and UV-VIS spectroscopic studies revealed that promoting effect of CP and MCP treatment was associated with the formation of the thermally stable carbene complexes Mo = CH₂ and Mo=CH-CH₃, arising from CP and MCP interaction with low coordinated MO⁴⁺ ions in photoreduced Mo/SiO₂ IR data showed fast reversible transformation of Mo=CH₂ to Mo=CH-CH₃ thus providing the first direct spectroscopic confirmation of a chain carbene mechanism of propene metathesis. A general scheme for CP and MCP interaction with photoreduced Mo/SiO₂ was proposed.     

Form birefringence and negative index change created by femtosecond direct writing in transparent materials

Although femtosecond lasers have proved to be of great utility for micromachining within bulk transparent materials, little is known about the fundamental physics that drive the process. Depending on the laser intensity delivered to the sample, any of three types of feature can be written into the glass. We observed that in the intermediate regime there is a correlation among the negative sign of the effective index change, the presence of anisotropic reflection, and birefringence. We propose a model that can explain all three principal characteristics. Results show that the local index change can be as high as 10(-1).     

Isomerization of isopropenylcyclobutane on silica gel under the conditions of chromatographic adsorptional analysis

Summary It was shown that, under the conditions of chromatographic adsorptional analysis on silica gel, isopropenylcyciobutane is isomerized with enlargement of the ring.     

Thermally poled glass: frozen-in electric field or oriented dipoles?

Evidence that a frozen-in space charge field causes the appearance of high quadratic nonlinearities in thermally poled glass is obtained from experimental tests of the ratio of nonlinear tensor components and the spatial distribution of the induced χ⁽²⁾. A mechanism to explain the fixation of the χ⁽²⁾ near the anodic surface is proposed.     

Role of the 2D surface state continuum and projected band gap in charge transfer in front of a Cu(111) surface

Electron capture by Li+ and H projectiles in grazing scattering from Cu(111) and Cu(110) surfaces is studied experimentally and theoretically. Whereas data for Cu(110) can be described by established theoretical methods treating resonant charge transfer with a free-electron metal, data for Cu(111) show pronounced deviations from this approach. We interpret our observations by the effect of the projected L-band gap of the Cu(111) surface. In particular, the quantum states of reduced dimension (2D surface state continuum) play a dominant role in electron transfer.