Structure and properties of hydroxylated surfaces of oxides

A review of works dealing with the IR spectra and structure of hydroxylated surfaces of oxides is presented. Influence of crystal structure and other factors on OH stretching modes, as well as data about bending vibrations of hydroxy groups are discussed. Experimental results are compared with data of computer simulations.     

CNDO study of the properties of the OH group

Using the CNDO method, a number of hydroxy-containing systems were calculated. The results are compared with IR spectroscopic data on the frequencies and acidity of surface OH groups and their dependence on the electronegativity of the atom to which the OH group is bonded.

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. - OH- , .

     

Quantum-chemical study of the optical properties of MgO surface hydroxy groups

Cluster models of MgO surface OH groups have been studied by the semi-empirical CNDO method. The calculated stretching vibration frequencies of OH bonds and localized electron excitation energies on the OH-groups are shown to depend on the oxygen atom coordination.

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OH- MgO. , OH- , OH-, .

     

IR-Spectroscopic Study of the Binding Isomerism of Adsorbed Molecules

This paper discusses the use of IR spectroscopy in the studies of isomerism in the binding of adsorbed molecules with a surface when a molecule may form several different surface species at the same site. Species whose geometry does not provide minimal adsorption energy can be considered as adsorption complexes in an excited state. The spectral manifestations of such a steric excitation are compared with the electronic and vibrational excitations of surface species. The sterically excited isomeric states existing in thermodynamic equilibrium with ordinary adsorption species are found and studied in detail. Examples are CO molecules bound through C and O atoms with metal cations in zeolites or with surface hydroxyl groups, the thiophene molecule via hydrogen bonding with silanol groups, and HD molecules dissociatively adsorbed on ZnO. A possible role of sterically activated isomeric states in catalysis is discussed.     

Distortions in IR spectra related to the registration conditions: I. The influence of the reflection from interfaces

We show that the contour of an absorption band of a thin layer of a liquid or a film of a solid compound deposited onto a substrate can be strongly distorted as a result of the reflection from the specimen surface or the interface with the substrate if the refractive index of the compound under study changes sharply in the range of the absorption band. We consider the theory of this phenomenon and ways of taking it into account in studies of the absorption spectra of films, liquids, and adsorbed molecules.     

Integrated absorption coefficient of adsorbed CO

The integrated absorption coefficient ε has been measured for the stretching band of CO adsorbed on a series of oxides and zeolites. From the temperature dependences of the spectra, ε has been estimated for CO molecules whose stretching frequency is lowered due to their bonding to cationic sites of the zeolite through the oxygen atom. In accordance with the predictions of the electrostatic model, ε decreases as the vibrational frequency of CO increases.     

Developmemt of the Researches on IR Spectroscopy of Surfaces at St. Petersburg University

Russian Physics Journal - The history of spectral studies of surface processes at St. Petersburg University from the pioneering pre-war experiments by Terenin and Kassparov to the present day is...