Hyperfine Magnetic Anomaly in Atomic Spectra of Rare-Earth Elements

The constants of the hyperfine splitting in the atomic optical spectra of the rare-earth elements – Nd, Eu, Gd and Lu – were measured. The method of laser resonance fluorescence in the parallel atomic beam was used. The values of the hyperfine magnetic anomaly were determined from the comparision of magnetic dipole constant ratios of the neighbouring odd Z or N isotopes for the different atomic levels. The connection of these values and the parameters of atomic and nuclear structure is discussed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Optical isotope shifts and changes in nuclear charge radii of stable Ti isotopes

Isotope shifts and hyperfine structures in three optical transitions of TiI have been investigated by using laser induced resonance fluorescence in a collimated atomic beam. From the isotope shifts data, changes of the mean square charge radii of the stable titanium isotopes have been determined for the first time. Using a combined analysis with muonic atom data on root mean square nuclear charge radii, improved model independent r ^21/2 values for the odd-even Ti isotopes have been obtained.     

Thermal desorption of ethylene on a clean iridium surface

The interaction of C₂H₄ with a polycrystalline iridium surface is studied by the flash desorption method at room temperature. Thermal desorption of ethylene and molecular hydrogen is observed. Analysis of the hydrogen peaks in the desorption spectra leads to the conclusion that the C₂H₃ species appear during ethylene adsorption on the surface at room temperature.

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C₂H₄ . . , C₂H₃.

     

Ethylene adsorption on a clear iridium surface

Adsorption of ethylene on an iridium surface proceeds with a high sticking coefficient. The species adsorbed at T=300 K have the structure of ethylidyne (C–CH₃). At T500 K the hydrocarbon molecules are decomposed on the surface forming a carbon layer.

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. , T=300 K (C–CH₃). 500 K, , .

     

Characterization and reactivity of Pt/Al2O3/SS thin films

Summary A catalytic system was obtained by impregnation with platinum of thin alumina films electrochemically deposited on stainless steel. The composition, morphology and structure of the Pt/Al2O3/SS and Pt/CeO2/Al2O3/SS samples were characterized by XPS, SEM and BET. Catalytic tests of the samples were performed in a stoichiometric gas mixture.     

The inhibitory activity of natural phenolic antioxidants in the oxidation of lipid substrates

The suppression of the oxidation of triglyceride and methyl esters of lard and olive and sunflower oils by additives of natural phenolic acids (hydroxy and methoxy derivatives ofpara-hydroxybenzoic and cinnamic acids) at 100 °C was studied. The rate constants of the interaction of these acids with peroxyl radicals in the oxidation of cumene at 60 °C were determined by the chemiluminescence method. Caffeic acid is the most efficient lipid antioxidant, exceeding ionol and α-tocopherol. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1119–1122, June, 1997.     

Coadsorption of oxygen and acetylene on a clean iridium surface

The interaction between oxygen and acetylene is investigated at 140T500 K. Information on the reaction products is obtained from XPS and UPS studies of a surface covered with one of the reagents and exposed to the effect of the other. Carbon monoxide is the main product of C₂H₂ oxidation. The presence of adsorbed atomic oxygen is a necessary condition of the catalytic oxidation of C₂H₂ on Ir.

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140 KT500 K. XPS UPS , -. C₂H₂. C₂H₂ Ir.

     

Hyperfine splitting of the odd 4 F J o , 2 P J o and 4 S J o LaI multiplets

High resolution spectra of LaI lines recorded in the R6G region by laser-induced resonance fluorescence method show well resolved hyperfine structures. The analysis of the hyperfine structure of seven LaI transitions is presented here. It has allowed the deduction of magnetic dipole and electric quadrupole constants of all levels belonging to the excited odd parity multiplets: ⁴ F ^o (J = 3/2-9/2), ² P ^o (J = 1/2,3/2), and ⁴ S ^o (J = 3/2). Some of the results are new and some of them present improved values of the hyperfine splitting constants.     

Hydrophobization of glass surface by adsorption of poly(dimethylsiloxane)

Silica or glass particles are introduced in a poly(dimethylsiloxane) (PDMS) matrix for various applications. A particular feature of these systems is that PDMS adsorbs on the surface of the dispersed particles, thus rendering them more hydrophobic with time. The mechanism of this process of in situ hydrophobization is still poorly understood. The major aims of the present study are (1) to quantify the rate of surface hydrophobization by PDMS and, on this basis, to discuss the mechanism of the process; (2) to compare the contact angles of surfaces that are hydrophobized by different procedures and are placed in contact with different fluid interfaces-PDMS-water, hexadecane-water, and air-water; and (3) to check how the type of surfactant affects the contact angles, viz., the effective hydrophobicity of the surface. We present experimental results for the kinetics of hydrophobization of glass surfaces, which are characterized by measuring the three-phase contact angle of glass-surfactant solution-PDMS. The data reveal two consecutive stages in the hydrophobization process: The first stage is relatively fast and the contact angle increases from 0 degrees to about 90 degrees within several minutes. This stage is explained with the physical adsorption of the PDMS chains, as a result of hydrogen-bond formation with the surface silanol groups. The second stage is much slower and hours or days are required at room temperature to reach the final contact angle (typically, 150-160 degrees). This stage is explained as grafting of the PDMS molecules on the surface by chemical reaction with the surface silanol groups. If the glass surface had been pretreated by hexamethyldisilazane (HMDS), so that CH(3) groups had blocked most of the surface silanol groups, the first stage in the hydrophobization process is almost missing-the contact angle slowly changes at room temperature from about 90 degrees up to 120 degrees. The experiments aimed to compare several hydrophobization procedures showed that PDMS ensures larger contact angle (more hydrophobic surface) than grafted alkyl chains. The contact angles at the PDMS-water and hexadecane-water interfaces were found to be very similar to each other, and much larger than that at the air-water interface. Interestingly, we found that the ionic surfactants practically do not affect the contact angle of PDMS-hydrophobized surface, whereas the nonionic surfactants reduce this angle. Similar trends are expected with silica surfaces, as well.     

H/D isotope exchange during ethylene adsorption on a clean iridium surface

The H/D isotope exchange of C₂D₄ adsorbed on an Ir surface has been studied by the thermal desorption method. Only deuterium atoms detached from the molecule after its adsorption on the metal surface participate in the exchange with a relatively high rate.

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H/D C₂D₄, Ir, . , , .