Experimental structural and conformational studies of carbonyl molecules in the ground and lower excited states

Experimental data (obtained by the authors and taken from the literature) on the structure and conformations of carbonyl molecules in the ground and lower excited electronic states are presented. The structure of carbonyl fragments, the orientation of substituent groups, the energy of the molecules in excited states, and the potential functions of the internal rotation and inversion are considered. The structural similarities of the molecules are discussed. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 269–285, March–April, 1995. Translated by I. Izvekova     

Spontaneous raman spectroscopic study of the association of liquid γ-butyrolactone molecules

Self-association of γ-butyrolactone molecules in pure liquid state and in nonpolar solutions is studied by spontaneous Raman spectroscopy. The constant and the enthalpy of formation of cyclic dimers in liquid γ-butyrolactone are calculated. Ufa State Aircraft Technical University. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 6, pp. 1099–1103, November–December, 1996. Translated by L. Smolina     

Fragment calculation of electronic structures of polyatomic molecules in the ground state. II. A method of delocalized states of fragments

A fragment method is proposed to calculate the electronic structures of polyatomic molecules in the ground state. Localization and delocalization of the electronic states of molecular fragments are calculated simultaneously. The compact formulation of the method allows algorithmically efficient calculations of the electronic structures of interacting molecular fragments as well as of the whole molecules. V. I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 395–400, May–June, 1995. Translated by I. Izvekova     

Phase and structure transformations in water microclusters

The behavior of 12- and 14-molecule water microclusters with ST2 potential in the range of 50–325 K is studied by the molecular dynamics method. Structure and phase transitions, including evaporation of molecules from the clusters and transition through the percolation threshold via hydrogen bonds, were found. Topological, temporal, and energy characteristics of the bond network are analyzed based on the dynamic criterion of hydrogen bonding. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurmal Strukturnoi Khimii, Vol. 35, No. 1, pp. 64–70, January–February, 1994. Translated by L. Chernomorskaya     

Spatial localization and dynamics of water molecules with good tetrahedral surroundings

The local structure of the molecular- dynamic model of water (729 particles at 300 K) is analyzed by isolating molecules whose surroundings differ slightly in configuration from a regular tetrahedron. These molecules are not randomly distributed in space but form nanometer clusters having a fractal structure. In these clusters, molecules are less mobile than the model molecules in general;their self- correlation function of rate and the density of vibrational states also differ from the average characteristics of the system. Translated fromZhumal Strukturnoi Khimii, Vol. 38, No. 4, pp. 713–722, July–August, 1997.     

Fragment calculation of electronic structures of polyatomic molecules in the ground state. I. A method of intermediate fragment

A method is proposed for fragment calculation of electronic structures of polyatomic molecules in the ground state. The wave function of a molecule in the ground state in single-determinantal representation of a closed shell is employed. The concise formulation allows efficient calculation of the electronic structures of polyatomic molecules taking into account possible charge transfer between interacting molecular fragments. V.I. Vernadskii Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 3, pp. 387–394, May–June, 1995. Translated by I. Izvekova     

Influence of molecular top deformations on the internal rotation barrier

The influence of molecular top deformations on the potential barrier is investigated. For some ethane-like molecules, it is shown that the deformation makes a pronounced contribution to the height of the torsion barrier. Orenburg State Pedagogical Institute. Translated fromZhurnal Struktumoi Khimii, Vol. 36, No. 2, pp. 356–358, March–April, 1995. Translated by L. Smolina     

Force fields of halide-substituted methane derivatives

The paper describes methods for determining the force fields of large sets of molecules which share the common property that in their constituent groups of molecules the equivalent force constants always change monotonically with the properties of substituent atoms belonging to the same subgroup of the periodic table. The force fields of the CH_4−nX_n (n=0–4, X=F, Cl, Br, I) molecules of the methane series are obtained. The applications of these force fields are discussed. In particular, they can serve as a basis for a data bank of the force fields of fragments suitable for constructing the force fields of more complex molecules. Russian Scientific Center “Applied Chemistry”, St. Petersburg. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 250–256, March–April, 1996. Translated by I. Izvekova     

Prephase state in 2-bromo-2-nitropropane-1,3-diol crystals: Structural aspects and IR spectra

This paper is a continuation of our series of publications dealing with crystal-lattice processes occuning on heating and at temperatures near the transition point and accompanied by structural changes in discrete molecules and in the crystal structure as a whole. The prephase state of 2-bromo-2-nitropropane-1,3-diol crystals and the transition from monoclinic to cubic phase are studied by IR spectroscopy at 296–391 K. Translated fromZnumal Strktumo, Chimii, Vol. 41, No. 2, pp. 294–299, March–April, 2000.     

Study of exciton transport in luminescent molecular nanoclusters using energy traps

We used a squarylium dye SQ as a specific exciton trap for J aggregates of the amphiphilic cyanine dye amphi-PIC. The exciton transport parameters in amphi-PIC J aggregates were estimated using a modified Stern–Volmer equation. We found that SQ quenches 50% of the luminescence of amphi-PIC J aggregates for a ratio of 1 SQ molecule per 80 amphi-PIC molecules. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 50–53, January–February, 2009.     

S 1←S 0 vibronic spectra and inversion potentials in theS 1 states of acetyl and formyl halides

The potential functions of inversion in the S₁ states are determined from the inversion transitions (out-of-plane C=O vibrations) found in the S₁←S₀ vibronic spectra of acetyl halide molecules. The high intensities of the hot inversion transitions are explained by the high probabilities of these transitions. The literature values of the inversion potentials (equilibrium values of angles formed by the C=O bonds deviating from the planes) of formyl halide molecules in the S₁ states are refined. The inversion potentials of formyl and acetyl halides are similar. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 316–321, March–April, 1995. Translated by L. Smolina     

Estimation of the densities of solutions using the geometrical parameters of their component molecules

A new model based on certain physical concepts of interatomic interactions is proposed for simulating the volume characteristics of molecules that allow reliable estimations of the densities of substances and solutions. The model is used to calculate the solution densities for six substances within wide concentration ranges. Chelyabinsk State University. Translated fromZhurmal Strukturnoi Khimii, Vol. 36, No. 5, pp. 823–827, September–October, 1995. Translated by I. Izvekova     

Local structure of solvation of nonpolar chains in nonpolar solvents at infinite dilution

The SSOZ (site-site Ornstein-Zernike) equation is used to study the local structure of solvation of linear nonpolar molecules in nonpolar solvents. The atom-atomic interaction potentials are described by the Lennard-Jones potential. The chain-solvent atom-atomic pair correlation functions are calculated in relation to the chain length (number of atoms), solvent density, and the ratio of the geometrical parameters of solvent and chain atoms. Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 4, pp. 742–749, July–August, 1996. Translated by L. Smolina     

Molecular dynamic study of stabilization of the Cl−−Cl− anion pair in steam

This paper studies the formation of a stable anion pair as a result of cluster interactions with water molecules (the number of molecules n=4, 6, 8, and 14). The hydration shells of the clusters obtained in a preliminary calculation are destructed to form closed chains of properly oriented water molecules in the space between the anions. The type of the resulting structure depends on the number of shared water molecules. The character of stabilization of the anion pair, determined by calculating different energy terms, also changes as n increases. The cyclic structures obtained in the region of the anion pair differ considerably from the structure of isolated Cl⁻ (H₂O)_n clusters and that of the aqueous solution of NaCl. The capture of water molecules by the anion pair is manifested in the nucleation of industrial steam. Institute of Thermal Physics, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 289–298, March–April, 1996. Translated by L. Smolina     

Determination of the potential functions of molecular inversion from experimental data: Current state and problems

Various approximations of the method of determining two-well potential functions of molecular inversion from experimental data (geometrical parameters and inversion level energies) are considered. The potential of the method is illustrated by reference to carbonyl molecules in the lowest excited states. Some of the current problems are discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 947–961, September–October, 1998     

Energy characteristics of structures in aqueous solutions of sucrose

Structures arising in sucrose solutions of various concentrations are modeled. A computer simulation by the molecular mechanics method proves the existence of three aqueous sucrose structures, which depends on the ratio between water and sucrose molecules. The calculated data are in good agreement with the experimental results obtained by different methods. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 5, pp. 864–871, September–October, 1998.     

Molecular force fields obtained using the nonempirical stabilizer of the regularizing functional

A new approach to the analysis of the force fields of polyatomic molecules is discussed. The results of quantum chemical calculations in combination with experimental data are used in a regularizing procedure, where the nonempirical matrix of the force constants determines the stabilizer of Tikhonov's functional. The use of stable numerical methods allows the specific modeling of the force fields of polyatomic molecules with due account of rotational isomerism. M. V. Lomonosov Moscow State University, Chemical Faculty. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 204–216, March–April, 1995. Translated by I. Izvekova     

Crystal-chemical mechanism in the fundamental absorption of MgO crystal

Correlations between structural, thermal, and optical properties of MgO are shown as linear dependences of the energy ε of the photons absorbed by the crystal on the enthalpy of sublimation ΔH of the crystal to molecules, atoms, ions, and electrons. This dependence holds true only if in different schemes of crystal sublimation the values of ΔH are calculated for the cell MgO rather than its formula unit. M. V. Lomonosov Moscow State University, Geological Faculty. IGEM, Moscow. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 283–288, March–April, 1996. Translated by I. Izvekova     

Stereochemical analysis by simplex representation of molecules

Stereoanalysis of molecules by partitioning a spatial structure into a system of simplices is described in detail. Potentialities of simplex representation of molecules in defining stereochemistry are demonstrated for chiral structures of various complexity and planar unsaturated molecules (“two-dimensional stereochemistry”). A concept of “stereochemical charge” is introduced. A. V. Bogatskii Physicochemical Institute, Ukrainian Academy of Sciences. Odessa State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 553–558, May–June, 1998.     

Vibrational structure of the electron transition to the second excited singlet state of pyridine N-oxide

The vibrational structure of the electron transition to the second singlet excited state of pyridine N-oxide has been studied. The frequency of the 0–0 transition is 34502 cm⁻¹. A computer-aided technique for the assignment of the frequencies of the normal vibrations of polyatomic molecules in the excited electronic states is proposed. The frequencies of the totally symmetric vibrations of pyridine N-oxide in the second singlet electronically excited state are assigned. N. G. Chernyshevskii Saratov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 350–355, March–April, 1995. Translated by I. Izvekova