Vibrations of dispersed silicas: A comparative

Four families of disperse amorphous silica representing different solid species modifications have been studied by inelastic neutron scattering at 10, 80 and 290 K. Doubly amplitude-weighted density of vibrational states (AWDS) have been obtained from the experimental time-of-flight spectra.     

Vibrational spectroscopy of dispersed silica: Aerosil

Conclusions A complex experiment has been carried out to examine the vibrational spectrum of Aerosil, and it has been found that the silanol group is the main active center of this type of dispersed silica. This fact conforms well with the previously advanced supposition that the structure of the core of silica is of a closed type in this case.The experimentally measured vibrational spectrum of the adsorbed water is practically completely described by a model in which one silanol center reacts with a water cluster. This agrees with the fact that chemical hydrophobic reactions take place on the surface of the usual commercial, i.e.,wet Aerosil. Since water is adsorbed as a cluster around one center, then in the presence of the usual 2. wt. % of water, a large part of the surface will be free of water and available for other reactions.It is natural that the above-considered simple models do not permit explanation of all the details of the observed spectra and a large amount of work will have to be carried out with more complicated models.Patrice Lumumba Peoples's Friendship University, Institute of Surface Chemistry, Ukrainian Academy of Sciences. Joint Institute of Nuclear Research. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 66–75, July–August, 1992.     

Computational modeling of amorphous silica. 2. Modeling the initial structures. Aerosil

A qualitative algorithm for constructing large clusters of aerosil model structures is used. According to this algorithm and the classification of amorphous silicas, aerosil is classified with tectosilicas, which are characterized by close packing of silicon-oxygen tetrahedra. Two quantitative algorithms for constructing large close-packed clusters are proposed. The structures of the clusters having from 10 to 24 silicon atoms, completely optimized by quantum chemical methods, were obtained. Small, medium, and large clusters for modeling the local and collective properties of atomic and functional group packing in the aerosil structure are distinguished. Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Struktumoi Khimii, Vol. 35, No. 3, pp. 16–26, May–June, 1994. Translated by O. Kharlamova     

Computational chemistry of the silicon nitride surface. 2. Binary hydroxylamine complexes. Geometry and bond energies

In order to study the silicon nitride surface it is interesting to consider hydrogen-bonded complexes with hydroxyl and amine key groups (OH...O, OH...N, NH...O, and NH...N). To investigate the behavior of the above bonds, we considered the water, ammonia, and hydroxylamine dimers and the binary hydroxylamine complexes with water and ammonia. The results of this work are compared with the data obtained by an ab initio method. Russian University of Peoples' Frienfship. Translated fromZhurnal Strukturnoi Khimii Vol. 37, No. 1, pp. 29–47, January–February, 1996. Translated by I. Izvekova     

Spectroscopy of Molecualr Crystals: A Bibliography for 1975

Abstract

Our previous thermodynamical approach was reexamined to study phase transition of anion radical salts, [(C₆H₅)₃PCH₃]⁺ _{1 ? x}[(C₆H₅)₃AsCH₃]⁺ _x(TCNQ)^? ₂,(0≤x≤1). The mechanism of the phase transition of the solid solution at 1 atm pressure was confirmed to be αy [(C₆H₅)₃PCH₃]⁺ _{1 ? x}[(C₆H₅)₃AsCH₃]⁺ _x(TCNQ)^? ₂,(0≤x≤1) βy, and the volume change assoiated with the phase transition was estimated to be ΔV =-1.3 (1-x) cm³/mol.     

Computer modeling of assembly of atoms in an electric field

A computer modeling of events that occurred under the scanning tunneling microscope (STM ) tip was considered from a chemical standpoint. The DYQUAMOD, semiempirical dynamical-quantum chemical program system, which well manifested itself in a quantitative studying of nano-sized objects, was transformed into the DYQUAFIELD program system involving an external electrostatic field. The fields of changeable configurations were simulated by a set of up to 200 point charges. Atomic system modeling was focused on obtaining local electron density (LED ) as well as on the object chemical transformations caused by the field. This article presents the results of simulating LED of differently originated graphite films, of a field action on a set of stable molecules, and of an irreversible in-field reconstruction of the diamondlike film surface, which demonstrates a possible nano-sized memory element creation. © 1996 John Wiley & Sons, Inc.     

Structure-sensitive mechanism of nanographene failure

The quantum-mechanochemical-reaction-coordinate approach has disclosed atomically matched peculiarities that accompany the deformation-failure-rupture process occurring in nanographenes. The high stiffness of the graphene body is provided by the benzenoid unit. The anisotropy of the unit mechanical behavior in combination with different configurations of the unit packing with respect to the body C-C bond chains forms the ground for the structure-sensitive mechanism of the mechanical behavior that is drastically different for two different deformation modes. The zig-zag deformation mode is particularly manifested with the formation of one-atom chains. The approach allows tracing a deformation-stimulated change in the chemical reactivity of both the nanographene body and its individual atoms.     

Spectroscopy of Molecular Crystals; A Bibliography for 1978

The 1978 Bibliography continues the series of annual issues of Bibliographies Spectroscopy of Molecular Crystals. The full list of these issues from 1957–1968 may be found in Molecular Crystals and Liquid Crystals, 6, 175, 1969. The issues for 1969, 1970, 197 1, 1972, 1973, 1974, 1975, 1976, and 1977 are published ibid, 14, 329 (1971), 17, 55 (1972), 19, 331 (1973), 26, 87 (1974), 30, 239 (1975), 33, 261 (1976), 39, 259 (1977), 46, 25 (1978) and 54, 59 (1979).     

Exciton—Phonon Luminescence of Perfect and Doped Naphthalene Crystals

The structure of phonon side bands in luminescence spectra of local excitons is investigated both theoretically and experimentally. A gradual transition from a spectrum behaviour peculiar for deep impurity centers (with wide phonon side band) to that peculiar for low temperature intrinsic luminescence (the side band becomes split into several bands corresponding to long wave lattice phonons) is investigated depending on the local exciton level depth. Experimental investigations of deuteronaphthalene solutions are presented.