Construction of basis vibration spectra of multicomponent systems. 3. Aerogel

Capillary-hollow silica (aerogel) is regarded as a three-component system consisting of the silica core, the hydroxyl component, and absorbed water. Its spectra of the doubly amplitude-weighted density of vibration states (AWDS), recorded at 10 K using the inelastic neutron scattering, were aecomposed into the spectra of the components of the system. The study uses the difference correlation technique based on the postulated lack of correlation between the basis spectra. The decomposition has been made by constructing physically significant basis spectra satisfying the criterion of zero coefficient of linear correlation, for the starting and modified samples of aerogel AG200.Russian University of People's Friendship, Unified Institute of Nuclear Research. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 29–38, July–August, 1993.Translated by L. Smolina     

Method for the construction of basis spectra of multicomponent systems. The zero correlation coefficient criterion

A new method is proposed for factoring the spectrum of a multicomponent system when the basis spectra of its components are unknown and the set of the weighting coefficients in the initial spectrum is incomplete. At the basis of this method is the postulate that there is no correlation between the basis spectra. A physically significant basis is constructed by linear algebra methods using this postulate. The components of the basis satisfy the zero linear correlation coefficient criterion. This method was successfully tested for two two-component systems, whose basis spectra are a priori not correlated.Russian International Friendship University and Joint Institute for Nuclear Research, Dubna. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 44–53, January–February, 1993.     

Spectroscopy of Molecular Crystals,A Bibliography for 1982

The 1982 Bibliography continues the series of annual issues of Bibliographies Spectroscopy of Molecular.     

Broken spin symmetry approach to chemical reactivity and magnetism of graphenium species

The basic problem of weak interaction between odd electrons in graphene and silicene is considered in the framework of the broken spin symmetry approach. This approach exhibits the peculiarities of the odd-electron behavior via both enhanced chemical reactivity and magnetism.     

Fullerene-silica complexes for medical chemistry

A quantum-chemical study of the interaction of C₆₀ fullerene with nanosized silica was performed. It was demonstrated that a fullerene molecule forms a weakly bound complex with a pyrogenic silica (Aerosil) particle only via the interaction with the silanediol groups of the hydroxyl covering on the particle. By contrast, a fullerene molecule is not bonded to an individual siloxane cycle, and, therefore, fullerosilica gel is formed due to the retention of fullerene molecules in pores of silica gel as a result cooperative action of the siloxane cycles comprising the pore. In both cases, the predicted medico-biological action of medicinal preparations is due to the radical-like and donor-acceptor characteristics of the C₆₀ molecule.     

Luminescence spectra and adsorption characteristics of naphthalene on various metal-substituted forms of type X zeolite

The low-temperature luminescence spectra of samples obtained after adsorption of naphthalene by metal-substituted type X zeolites are examined. In zeolites of the first group (LiNaX, NaX, KNaX, RbNaX, CsNaX, MgNaX, CaNaX, ZnNaX, SrNaX, and BaNaX), the luminescence spectra of all the systems studied are largely the same. In the analysis of these spectra, naphthalene molecules which are physically sorbed and those bound by donor-acceptor interaction are distinguished. In forming the adsorbed charge-transfer complex (CTC), the naphthalene molecules behave as electron donors. The elements of the zeolite lattice serve as the acceptors. With zeolites of the first group, oxidation of the anphthalene, occurring in the adsorbed phase on contact with air, is observed spectroscopically. In constrast, zeolites of the second group (CoNaX, NiNaX, CuNaX, AgNaX, and CdNaX) are characterized by individual spectra due to the formation of a CTC between the naphthalene molecule and the metal present in the lattice. None of the five systems displayed oxidation of the naphthalene on contact with air.In conclusion, we wish to express our deep appreciation to V. L. Broude for fruitful discussions while considering the experimental results.     

Computational modeling of amorphous silica. 3. Modeling the initial structures. Silica gel

A qualitative algorithm for construction of large clusters of silica gel model structures is used. According to this algorithm and in line with our classification of dispersive silicas, silica gel is regarded as cyclosilica, which is characterized by loose packing of the cycles of silicon-oxygen tetrahedra. A model of silica gel structure is proposed, where the primary structural fragments are hollow frameworks with a network surface. The units of the surface network are formed by nonplanar [SiO₄] chain cycles of various sizes. This structural model makes it possible to explain the peculiarities of the vibration spectra of the framework, hydroxyl, and aqueous components of silica gels. Institute of Surface Chemistry, Ukrainian Academy of Sciences. Russian University of Peoples' Friendship. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 3, pp. 27–34, May–June, 1994. Translated by O. Kharlamova     

Fine structure of the spectra of magnetic particles in the vortex state and their ordered arrays

A low-frequency (the frequency ω_VPM is in the sub-GHz range) mode exist for submicron magnetic particles in the vortex state. This mode corresponds to oscillations of the vortex center. The other modes form doublets with higher (several gigahertz) frequency and small (about ω_VPM) splitting. Collective oscillations exist for lattices of such particles. The dependence of the frequency of these modes on the quasi-momentum can be nonanalytic.