Quantum-chemical interpretation of the isomer shift on tin compounds

Molecular orbital calculations (EHT, IEHT, IEHT + Madelung correction) have been applied to a series of tin halides. A calculation procedure is described to derive the charge density of the electrons at the nucleus (0). The dependence of the isomer shift on covalency effects is demonstrated. The influence of the outer charge of the molecules on the isomer shift is shown. The relative change of nuclear charge radius R/R is calculated for tin.     

Quantum-chemical studies of the interaction between furan and pyridine molecules and surface fragments of vanadium oxide catalysts

CNDO/2 studies of the interaction between furan and pyridine molecules and coordinatively unsaturated surface centers of vanadium oxide catalysts indicate that these molecules are more tightly bound and undergo more substantial changes in their electronic structure upon coordination to centers, containing reduced vanadium ions.

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Quantum-chemical approach to optimization of the synthesis conditions of two-component phosphorus-titanium oxide structures on silica surface

The features of formation of a two-component phosphorus-titanium oxide coating on the silica surface by sequential treatment of the substrate with POCl₃ and TiCl₄ vapors were analyzed with application of quantum-chemical approaches. An experimental synthesis of two-component coatings under conditions selected on the basis of theoretical calculations yielded coatings whose composition corresponded to the model predictions. The structure of the resulting coatings was studied by Fourier-transform IR spectroscopy, electronic diffuse reflectance spectroscopy, and chemical analysis.     

Mechanism of the condensation of acetone on the surface of aluminum oxide

The condensation of acetone on the surface of aluminum oxide was studied by the methods of the temperature-program surface reaction, mass spectrometry, and infrared spectroscopy, and a reaction mechanism is proposed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 333–338, May–June, 1985.     

Friction force microscopy of alkylphosphonic acid and carboxylic acids adsorbed on the native oxide of aluminum

Monolayers of alkylphosphonic acids (APA) and alkylcarboxylic acids (ACA) on magnetron-sputtered aluminum films have been investigated by friction force microscopy (FFM), contact angle measurement, and polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Clear evidence has been provided from PM-IRRAS that friction coefficients, determined from FFM data, may be correlated directly with variations in adsorbate molecular structure. The friction coefficient increased with the length of the adsorbate molecule, but reached a limiting value when the alkyl chain of the adsorbate contained eight carbons in the case of APA or 12 carbons in the case of ACA. For a given alkyl chain length, APA monolayers yielded coefficients of friction that were similar to those of monolayers of alkylthiols of the same length, but smaller than those of ACA. These data indicate that APA monolayers are better ordered than ACA monolayers. These inferences were supported by PM-IRRAS data, which enabled the density of gauche defects to be estimated and correlated with variations in the coefficient of friction.     

Effect of nature of templates on formation mechanism of aluminum oxide mesoporous structure

Mesoporous aluminum oxide is produced by the sol-gel method from aluminum isopropoxide using molecular structures of a cationic polyelectrolyte (polyethylenimine) and dodecylamine micelles as nanotemplates. The mechanism for the formation of mesophases of hybrid materials in colloidal systems upon template synthesis is discussed.     

Nature of the centers on the surface of oxide catalysts and the forms of adsorbed toluene

IR spectroscopy has been used to analyze the forms of toluene adsorbed on various oxides, differing in the nature of their surface centers: TiO₂, CuO, V₂O₅/Al₂O₃, V₂O₅. The form of adsorption is found to depend on the nature of the surface centers of the oxide. When coordinationally saturated cations are involved complexes of toluene are formed, while if surface oxygen is involved benzoate structures are produced. The temperature at which the latter begin to be formed depends on the strength of the bond between oxygen and the surface. It was shown that the presence of acidic hydroxyl groups on the surface of the oxide leads to proton transfer to the aromatic compound to give carbonium ions. The nature of the interaction is then determined by the mobility of the proton on the surface and the basic strength of the adsorbed molecule. The possibility of identifying such compounds spectroscopically is discussed.Translated from Teoreticheskie i Éksperimental'naya Khimiya, Vol. 26, No. 6, pp. 710–715, November–December, 1990.     

Quantum-chemical studies of olefin activation on gallium oxide

The interaction of propylene with gallium oxide has been studied by the MINDO-3 method using a cluster model. It is shown that the energy barrier against allyl C–H bond dissociation is mainly determined by the Coulomb repulsion between the molecule and the central metal ion. Interaction of the dissociating hydrogen with the oxygen of the fragment ensures the stabilization of the system.

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MINDO-3 і . , C–H , , . і .

     

Raman spectra of pyridine adsorbed on a copper electrode

The surface enhanced Raman scattering (SERS) of pyridine adsorbed on a copper electrode was observed with 647.1 nm excitation and the dependence of the Raman intensity as a function of electrode potential was obtained for the most intense bands. The results are compared with reported intensity and frequency values for the silver/pyridine system.     

Studies on the nature of salicyl hydroxamate adsorption at the surface of neodymium oxide

Abstract

Adsorption of salicyl hydroxamic acid (SHA) on neodymium oxide (Nd₂O₃) surfaces was studied at different SHA concentrations. The adsorbed surfaces were examined using X-Ray Diffraction (XRD) and Laser Raman Spectroscopy (LRS). XRD results show that the oxide remains intact until stoichiometric amounts equivalent to Nd(SHA)₃ were exceeded. At lower concentrations, the behavior appeared to be an ion exchange of SHA with hydroxide as well as carbonates and chlorides. Results are attributed to a monolayer of chemisorbed SHA at low concentrations and multilayers of surface precipitated Nd(SHA)₃ at higher concentrations. LRS corroborated these findings. Peaks from the C-H stretching band and C?=?N vibration bands were identified and areas under the peaks were quantified. Formation of the hydroxamate compound was ascertained from the C?=?N bands around 1597?cm^?1. It was concluded that chelation occurs through chemical bonding of SHA with surface Nd confirming chemisorption and with trivalent Nd confirming surface precipitation. Thermodynamic calculations in the form of solubility speciation diagrams suggest that chemisorption predominates at moderate pH between 6 and 9 and surface precipitation predominates at higher pH between 9 and 12. Adsorption isotherms were determined for the monolayer and found to yield free energy values between physisorption and chemisorption but, due to the reaction being ion exchange, it was concluded to be chemisorption.     

Photoluminescence of TiO2: effect of UV light and adsorbed molecules on surface band structure

The photoluminescence (PL) of TiO(2) at 529.5 nm (2.34 eV) has been found to be a sensitive indicator of UV-induced band structure modification. As UV irradiation occurs, the positive surface potential changes and shifts the depth of the depletion layer. In addition, reversible band bending due to the adsorption of the electron-donor NH(3) and CO molecules has been observed in measurements combining PL with FTIR surface spectroscopy. It has been found that the O(2) molecule acts in two ways: as a reversibly adsorbed electron-acceptor molecule and as an irreversibly adsorbed molecule that heals natural oxygen vacancy defects in the near-surface region.