Vibrational assignments and force field calculations for trimethylarsenic dichloride,dibromide and their deuterated analogs

Raman and infrared spectra have been recorded for trimethylarsenic dichloride, dibromide and their deuterated analogs and vibrational assignments were made for the skeletal modes of these compounds. The spectra of the dichloride and its deuterated analog were interpreted in terms of a trigonal bipyramidal structure, D_3h symmetry, whereas the spectra of the dibromides were interpreted using the ionic model, [(CH₃)₃AsBr]⁺Br⁻, having C_3v symmetry. Using a generalized valence force potential field, normal coordinate analyses data were obtained for the dichloride and the dibromide. Included in this data are potential energy distributions for a set of symmetry coordinates. The force fields obtained for the dichloride and dibromide were used to calculate frequencies for the corresponding deuterated compounds. The discrepancies between the observed and calculated frequencies for the deuterated compounds are discussed in terms of the assumptions made.     

Preparation of solid solutions of deuterated triglycine sulphate and concentration dependence of some of their ferroelectric properties

A number of ferroelectric solid solutions (N[H, D]₂CH₂COO[H, D])₃[H, D]₂SO₄ have been prepared in the concentration range of the initial components of 0 to 94·2%. Moreover, the parameters of the Curie-Weiss law have been measured as a function of the concentration of the initial components. The course of the phase transition position and of the Curie constant as a function of the concentration is discussed by means of Janovec's thermodynamic theory of ferroelectric solid solutions. Mixed crystals cannot be classified as perfect solid solutions, but their behaviour may be expressed by regular approximation.     

Broadening of triplet-triplet absorption band in molecular structures with different spatial dimensionalities

Within the framework of a dipole approximation, the form of the light absorption band for exciton transitions between triplet zones in one-, two-, and three-dimensional periodic molecular structures is calculated. Allowance is made for exciton attenuation as a frequency-independent parameter. The analytical expressions obtained make it possible to analyze the band for molecular structures of different spatial dimensionalities as a function of the difference in bandwidths, attenuation, and lattice temperature. Institute of the Surface Chemistry, National Academy of Sciences of Ukraine, 31, Nauka Ave., Kiev 252022, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 5, pp. 586–590, September–October, 1997.     

Numerical micromagnetics of interacting superparamagnetic nanoparticles assembled in clusters with different dimensionalities

We analyze here the equilibrium magnetization state of densely packed interacting superparamagnetic nanoparticles assembled in clusters of various sizes and dimensionalities by comparison with the non-interacting case. We demonstrate that the average magnetization of individual particles is strongly increased in linear chains aligned parallel with the external magnetic field. Two-dimensional (2D) distributions of superparamagnetic nanoparticles present weaker increases of their average magnetization with respect to the non-interacting approximation whereas volume distributions (3D) are almost equivalent with the non-interacting case. A large number of nanoparticles densely packed in 2D superparamagnetic clusters present almost the same magnetic moment as infinite superparamagnetic chains. The effect of mutual interactions on the total magnetic moment of 3D surfaces (spheroids with various aspect ratios) uniformly covered with densely packed monolayers of superparamagnetic nanoparticles is also investigated.     

Infrared and Raman spectra and vibrational assignments of diiodomethane and its deuterated analogs

The infrared (from 4000 to 100 cm^?1) and Raman spectra of CH₂I₂ and CD₂I₂ have been recorded in the liquid and gaseous phases. Assignments have been made for all observed bands and, in the case of CH₂I₂, compared with those previously reported. Some bands appearing in the CD₂I₂ spectrum have been attributed to the presence of CHDI₂. The wavenumbers of the fundamental bands of CHDI₂ have been calculated from those of CH₂I₂ and CD₂I₂ using Brodersen and Langseth's rule, and compared with those observed in the CD₂I₂ spectrum.     

Quantum-chemical modeling of spectroscopic and photophysical properties of ethylene-bridged octaethylporphyrin dimer

In a solution, a dimer of octaethylporphyrin meso-linked by an ethylene bridge (tbis-OEP) may adopt conformational forms the lifetimes of the S ₁ state of which are considerably different (7 ns for the P′ and ∼6–9 ps for the P and U forms). In this work, we propose new structural models for these forms based on calculations of the geometry, vibrational, and electronic states of tbis-OEP and related model systems using methods of the density functional theory. The modeling of the absorption spectra of tbis-OEP in toluene shows that they can be well described assuming that the distribution of conformers with values of the dihedral angle α (which determines the positions of the macrocycles with respect to the ethylene bridge) in the range of 10°–90° is Boltzmanian. We have found that a considerable difference between the spectral properties of tbis-OEP in toluene and chloroform is related to particular features of the structure of the corresponding solvation complexes. Interactions with chloroform molecules in solution facilitate the predominant stabilization of conformers with α ∼ 90°, while, in the case of solvation complexes with toluene molecules, conformers with α ∼ 40° are more energetically favorable. Based on the optimization of the geometry of tbis-OEP in the S ₁ state and on the calculations of the matrix elements of vibronic interaction, we propose mechanisms by which a considerable shortening of the lifetime of the excited state of tbis-OEP and experimental regularities of variation of this parameter upon variation of the solution viscosity and freezing of the solution can be explained.     

Coexistence of glass and ferroelectric order in deuterated betaine phosphate0.05 betaine phosphite0.95 crystals

The dielectric spectra of ferroelectric hydrogen bonded betaine phosphate_0.05 betaine phosphite_0.95 (DBP_0.05DBPI_0.95) was investigated in the very wide temperature (300–20 K) and frequency (20–35 GHz) regions. The dielectric dispersion was analyzed in terms of distribution of relaxation times, using Tichonov regularization method. Strongly asymmetric and broad distribution of relaxation times below ferroelectric phase transition temperature T _c?≈?253 K clearly differs from the one that is usually observed in ferroelectrics. The observed disorder in deuterons system close to ferroelectric phase transition temperature is an embryo of coexistence ferroelectric order and dipolar glass disorder observed at low temperatures.     

Force of attraction between solids with different temperatures

The methods of fluctuation electrodynamics based on the theory of molecular Van der Waals forces are used to obtain an expression for the density of attraction force between two absorbing media with different temperatures, which are separated by a nonabsorbing plane-parallel layer. The spectral density of the force was calculated as a projection of the Maxwell stress tensor on the outer normal to the solid surface. The mean square characteristics of the fluctuction field of the solids are obtained using the generalized Kirchhoff’s law and Green’s function of the corresponding regular problem. The solution versions are obtained depending on the relation between the temperatures of interacting solids. It is shown that for equal temperatures of the solids the expression obtained yields the formula for the attraction force in the case of equilibrium. Institute of Physics of Microstructures, Russian Academy of Sciences, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 12, pp. 1495–1510, December, 1997.     

The vapor-phase Raman spectra and the ring-puckering vibration of some deuterated analogs of trimethylene oxide

The ring-puckering vibration has been observed in the Raman spectra of the vapor phase of several deuterated species of trimethylene oxide (α - d₂, β - d₂, α, α′ - d₄, and d₆). Only Δv = 2 transitions have a measurable Raman intensity. The line positions agree with infrared values to better than 0.5 cm⁻¹ in most cases and better than 1 cm⁻¹ in all cases. For all molecules the interpretation of the spectra is consistent with an essentially planar configuration having only a small barrier to inversion.     

The far-infrared spectra and ring puckering potential functions of several deuterated analogs of trimethylene sulfide

The far-infrared spectra in the region of 50–200 cm^?1 of several deuterated analogs of trimethylene sulfide (viz α-d₂, β-d₂, α,α′-d₄ and d₆) are reported. The bands are assigned to ring puckering transitions. The potential constants in the function, V(Z) = A(Z⁴ + BZ²), Z the reduced puckering coordinate, were determined for each compound separately. The barrier height, $\text{AB}{}^2\text{4}$, is found to vary upon isotopic substitution in the quadratic-quartic approximation.     

Investigation of structural evolution of hydrogen-bond networks of water clusters at 1 and 300 K

Computer simulation of water clusters (H₂O) _n , Na⁺(H₂O) _n and K⁺(H₂O) _n (n ?? 8) at temperatures of 1 and 300 K was carried out using the Monte Carlo method. All the types of the hydrogen-bond network structures at equilibrium configurations of the water clusters and, among them, the most probable ones at temperatures of 1 and 300 K, were detected. The analysis of the most probable types of hydrogen-bond networks at equilibrium configurations of water clusters revealed that clusters with n water molecules inherit the configuration of clusters with n ? 1 water molecules with an accuracy of one hydrogen bond.     

On the construction of some bioconjugate networks and their structural modeling via irregularity topological indices

The European Physical Journal E - In this article, we experimentally investigate the nonlinear behaviour of a viscoplastic film flow down an inclined plane. We focus on the nonlinear instabilities...     

Mathematical modeling of laser induced heating and melting in solids

An analytical method for treating the problem of laser heating and melting is developed in this paper. The analytical method has been applied to aluminum, titanium, copper, silver and fused quartz and the time needed to melt and vaporize and the effects of laser power density on the melt depth for four metals are also obtained. In addition, the depth profile and time evolution of the temperature of aluminum before melting and after melting are given, in which a discontinuity in the temperature gradient is obviously observed due to the latent heat of fusion and the increment in thermal conductivity in solid phase. Additionally, the calculated melt depth evolution of fused quartz induced by 10.6 μm laser irradiation is in good agreement with the experimental results.     

Quantum-chemical modeling of energy parameters and vibrational spectra of chain and cyclic clusters of monohydric alcohols

The specific peculiarities of alcohols such as heightened viscosity, boiling temperature and surface tension can be explained by the capability of their molecules to form relatively stable associates named clusters due to hydrogen bonding. In present work the stability of different chain-like and cyclic clusters of methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol and 1-hexanol was investigated by means of quantum-chemical simulation and particular by recently developed DFT exchange–correlation functional M06-2X. The relative stability of the cluster structure was evaluated by the total energy per molecule at low temperatures (where all alcohols exist in solid state) and by the changing of the free Gibbs energy upon cluster formation at the room temperature. For the verification of revealed results the conformity of calculated IR spectra of the most stable cluster structures with the experimental IR spectra at different temperatures was analyzed.     

Automatic mapping and modeling of human networks

Mobile telephones, company ID badges, and similar common devices form a sensor network which can be used to map human activity, and especially human interactions. The most informative sensor data seem to be measurements of person-to-person proximity, and statistics of vocalization and body movement measurements. Using this data to model individual behavior as a stochastic process allows prediction of future activity, with the greatest predictive power obtained by modeling the interactions between individual processes. Experiments show that between 40% and 95% of the variance in human behavior may be explained by such models.     

Switching dynamics and modeling of multi-domain Zr-Doped HfO2 ferroelectric thin films

HfO₂-based ferroelectrics have attracted attention as promising materials for advanced memory applications owing to their negative capacitance effect, high scalability, and full-CMOS compatibility. Accordingly, the switching dynamics of HfO₂ thin films have been actively discussed and simulated using the Landau-Khalatnikov equation (LK model). Although the simulated results agree with experimental results in many studies, there is a slight dissimilarity near the coercive field in the polarization-electric field curve. For accurate and general modeling, a new model that combines the conventional LK model and Euler's equation was proposed in this work. The model was examined under single-domain and multi-domain conditions. The simulated curves using the Landau-Euler method better fit with measured curves than those using the LK model.