Technical graphene (reduced graphene oxide) and its natural analog (shungite)

The wide structure and chemical-composition spectrum of the main technological material of molecular graphenics—reduced graphene oxide (RGO)—is explained from a quantum-chemical standpoint. The proposed concept is used to consider the results of experimental investigations of a natural analog of RGO, namely, shungite carbon, by high-resolution electron microscopy and nanopoint energy dispersive spectral analysis. The results obtained are used to propose an atomic-microscopic model for the structure of shungite carbon.     

Phonon Side Bands of Specular Optical Transitions in Molecular Crystals

Quantitative investigations of phonon side bands (PSB) in the small radious centers absorption and luminescence spectra of some impurity molecular crystals are presented. Three pairs of specular spectra were considered corresponding to three impurity systems: benzene-d ⁰ in benzene-d ⁶, phenol in benzene-d ⁰ and β-methylnaphthalene-d ¹⁰ in naphthalene-d ⁸. Analysis of the observed spectra revealed such PSB regularities.

1) The most common characterization of PSB spectra is the deviation of the PSB shape from specular symmetry.

2) The non-specularness of the PSB shape does not depend on whether the PSB integral intensities are equal or different.

3) There is an unambiguous correlation between the expression of the PSB non-specularness and the temperature variation of the phononless band half width and shift.

4) For weak transitions, the non-specularness of the PSB integral intensities is observed in addition to the PSB shape non-specularness.

For the first time the observed characteristics were explained quantitatively in terms of the deviation from the Condon approximation on the basis of one-phonon spectra substracted from the PSB observed.     

Two-dimensional magnetic solitons and thermodynamics of quasi-two-dimensional magnets

The article reviews two-dimensional magnetic solitons in a classical weakly-anisotropic Heisenberg magnets. Topological classification, structure, dynamical properties and thermodynamical contribution of 2D solitons to response functions of the magnet are discussed. Based on effective equations of motion we calculated the soliton contribution to the dynamical structure factor of ferromagnets and antiferromagnets both for localized topological solitons and magnetic vortices.     

Fullerenes as polyradicals

We present the investigation of the electronic structure of X₆₀ molecules (X=C, Si), containing 60 odd electrons with spin-dependent interaction between them. Conditions for the electrons to be excluded from the covalent pairing are discussed. A computational spin-polarized quantum-chemical scheme is suggested to evaluate four parameters—energy of radicalization, exchange integral, atom spin density, and squared spin— to characterize the effect quantitatively. A polyradical character of the species, weak for C₆₀ and strong for Si₆₀, is established.     

Multi-mode ground state interaction terms in C60-based electron donor-acceptor complexes

Quantum-chemical testing of donor-acceptor properties of binary molecular complexes, related to the singlet state, is suggested as QCh calculations of studied systems and their constituents by using both spin-nondependent (RHF) and spindependent (UHF) versions of the exploited computational tool. The avoided crossing of intermolecular interaction terms of neutral moleculesE _int (A ⁰ B ⁰) and molecular ionsE _int (A ⁺ B ⁻) causes a multi-mode character of the ground state term. The dependence of D-A complex properties on the type of the term, space positions of the term minimum, and the interrelation of the corresponding energies are discussed. The suggested approach has been applied to binary complexes C₆₀+X (X=TAE, TDAE, DMMA, COANP, 2Li, Mg).     

Construction of vibrational basis spectra of multicomponent systems 2. Silica gel

Silica gel is considered a three-component system consisting of a silica core, hydroxyl shell, and pore-retained water. Inelastic neutron scattering was used to obtain a set of amplitude-weighted vibrational state density (AWSD) spectra of two silica gel families SG20 and SG100 with mean pore diameter of 20 and 100 Å, respectively. The AWSD spectra were factored into the components of this system. The factoring method used is based on the postulate of lack of correlation of the basis spectra. The factoring was carried out by the construction of physically significant basis spectra satisfying the zero linear correlation coefficient criterion.Russian International Friendship University and Joint Institute for Nuclear Research, Dubna. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 1, pp. 64–76, January–February, 1993.     

Comparative analysis of vibration spectra of dispersive silicas and their components

Comparative analysis has been carried out on a set of partial basis spectra of the doubly amplitude-weighted density of vibration states (AWDS) of four dispersive silica: aerosil A380, silica gels SG20 and SG100 (with pore sizes 20 and 100 Å), and aerogel AG200 with mass density 200 kg/m³. The set of basis spectra includes the vibration spectra of frameworks, and of the hydroxyl and aqueous components of the surface zone of the above compounds. Aerosils, silica gels, and aerogels have been found to be radically different structural forms of amorphous silica, both from the viewpoint of their frameworks and their surface zones. The basis spectra considered represent a collection of fingerprints of the structure-dynamic properties of the compounds studied, which allows us to formulate a qualitatively new approach to computational modeling of dispersive silicas.Russian University of People's Friendship, Institute of Surface Chemistry, Ukrainian Academy of Sciences, Unified Institute of Nuclear Research. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 39–51, July–August, 1993.Translated by L. Smolina