Dispersion and polarization interactions of the strontium atom

Dispersion coefficients involving the 5s ^{2 1} S ^e and 5s5p ^1,3P ^o states of strontium are determined from a large basis configuration interaction calculation. Dispersion coefficients are presented for the strontium dimer and also for strontium interactions with hydrogen and the rare gases. Polarizabilities and oscillator strengths from some low lying states are also given. The ground state polarizability and that of the 5s5p ¹P ^o and 5s4d ¹D ^e states are very similar in size.     

New constraints on gruneisen parameters applications to equations of state for pressure markers

Abstract

“Regular” linear relations between shock and particle velocities, u_s = u_s0, + c · u_p, imply a divergence of the Hugoniot pressure p_H at a critical compression V _c/V _o = (c-1)/c, where the thermal pressure Δp _th = (γ/V)· ΔU _th = p _H-p _T becomes very large with respect to the cold (isothermal) pressure p _T at this compression. The Hugoniot relation for the total internal energy U _H results in this case in the relation γ_c = 2(c- 1) for the Grüneisen parameter in this region. Experimental data for the zero pressure value Γ_o and its derivative Γ_o together with theoretical data for the limiting value γ_∞ = 2/3, and the additional expenmental value γ_c are then used to determine the thermal (phonon) pressure with the common Mie-Grüneisen assumption.     

Raman spectra of asymmetric top molecules

A detailed analysis of the Raman-active v ₁, v ₃ (both A-type) and v ₅ (B_c -type) vibration-rotation bands of ethylene is presented. In addition to structural data simulation of the spectra yields values for the polarizability ratios of the totally symmetric bands, giving information on the polarizability ellipsoid as the molecule vibrates. v ₃ is shown to be perturbed by a c-type Coriolis interaction which complicates the interpretation of the negative value of the polarizability ratio required to match the observed spectrum.

The effects of asymmetry are pronounced; one result being the formation of heads in the ^R,PR _{K p} and ^R,P P _{K p} branches of low K _p in the v ₅ band.     

Kinetic fragility of binary and ternary glass forming liquid mixtures

The experimental studies of liquid fragility in miscible binary and ternary glass forming mixtures reveal a general observation of the negative deviation in fragility upon mixing from the linear average of those of the components. Further analyses from ideal, near ideal to non-ideal mixing modes show that the deviation magnitude does not increase monotonically with mixing enthalpy, and a moderate intermolecular interaction would generate a largest reduction in fragility. Four eutectic systems, methyl-o-toluate-methyl-p-toluate, ZnCl₂-AlCl₃, glycerol-water, and fructose-water, are studied to locate the composition where the largest fragility deviation occurs in phase diagrams. It is found that the compositions with the fragility minima do not coincide with the eutectic points. The results partly explain the experimental observation that the best glass forming region is not located at the eutectic composition.     

Orientational order parameter estimated from molecular polarizabilities – an optical study

An optical study of N-(p-n-alkyloxybenzylidene)-p-n-butyloxyanilines, nO.O4 compounds with the alkoxy chain number n?=?1, 3, 6, 7, and 10 has been carried out by measuring the refractive indices using modified spectrometer and direct measurement of birefringence employing the Newton's rings method. Further, the molecular polarizability anisotropies are evaluated using Lippincott δ-function model, the molecular vibration method, Haller's extrapolation method, and scaling factor method. The molecular polarizabilities α _e and α ₀ are calculated using Vuk's isotropic and Neugebauer anisotropic local field models. The order parameter S is estimated by employing the molecular polarizability values determined from experimental refractive indices and density data and the polarizability anisotropy values. Further, the order parameter S is also obtained directly from the birefringence data. A comparison has been carried out among the order parameter obtained from different ways and the results are compared with the body of the data available in the literature.     

Modulated Phase of a Potts Model with Competing Binary Interactions on a Cayley Tree

We study the phase diagram for Potts model on a Cayley tree with competing nearest-neighbor interactions J ₁, prolonged next-nearest-neighbor interactions J _p and one-level next-nearest-neighbor interactions J _o . Vannimenus proved that the phase diagram of Ising model with J _o =0 contains a modulated phase, as found for similar models on periodic lattices, but the multicritical Lifshitz point is at zero temperature. Later Mariz et al. generalized this result for Ising model with J _o ≠0 and recently Ganikhodjaev et al. proved similar result for the three-state Potts model with J _o =0. We consider Potts model with J _o ≠0 and show that for some values of J _o the multicritical Lifshitz point be at non-zero temperature. We also prove that as soon as the same-level interactionJ _o is nonzero, the paramagnetic phase found at high temperatures for J _o =0 disappears, while Ising model does not obtain such property. To perform this study, an iterative scheme similar to that appearing in real space renormalization group frameworks is established; it recovers, as particular case, previous work by Ganikhodjaev et al. for J _o =0. At vanishing temperature, the phase diagram is fully determined for all values and signs of J ₁,J _p and J _o . At finite temperatures several interesting features are exhibited for typical values of J _o /J ₁.     

Concentration and temperature dependent interaction studies using dielectric and thermodynamic methods on mixtures of anisole with o-toluidine and m-toluidine

Molecular interactions in mixtures of anisole with o-toluidine and anisole and m-toluidine have been studied at three different temperatures using the dielectric method with measurements of the static permittivity and permittivity at optical frequency. From the measured values, the Kirkwood correlation parameter, Bruggeman parameter, excess permittivity and thermodynamic excess free energy were computed for the mixtures. Positive and negative values of excess permittivity were obtained for both mixtures. The excess free energy for the anisole+o-toluidine mixture is positive at all three temperatures, whereas mixed values (positive and negative) are obtained for the anisole+m-toluidine mixture. Alignment of the dipoles in both mixtures was identified by Kirkwood factors. The investigation shows that the interaction between the components changes systematically with concentration and temperature and the change is minimum.     

The argon nuclear quadrupole moments

New standard values -116(2) mb and 76(3) mb are suggested for the nuclear quadrupole moments (Q) of the ³⁹Ar and ³⁷Ar nuclei, respectively. The Q values were obtained by combining optical measurements of the quadrupole coupling constant (B or eqQ/h) of the 3s²3p⁵4s[3/2]₂ (³P^o) and 3s²3p⁵4p[5/2]₃ (³D^e) states of argon with large scale numerical complete active space self-consistent field and restricted active space self-consistent field calculations of the electric field gradient at the nucleus (q) using the LUCAS code, which is a finite-element based multiconfiguration Hartree–Fock program for atomic structure calculations.     

Refractive indices, order parameter and principal polarizability of cholesteric liquid crystals and their homogeneous mixtures

Measurements of refractive indices (n_e,n_o) and birefringence (Δn) have been made in solid, cholesteric and isotropic phases of cholesteryl carbonate, cholesteryl stearate and their three homogeneous mixtures of concentration 0.25, 0.50 and 0.77 at varying temperature in the range of 18-35 °C. The results clearly indicates that various transitions are of the first order. For accurate measurement of Δn, a modified wedge method was used. Using n_e and n_o, principal polarizability (α_e,α_o), internal field factor (γ_e,γ_o) and order parameter (S) have been evaluated, and their temperature dependence discussed. The order parameter has been determined by using the isotropic internal field model (Vuks approach) and the anisotropic internal field model (Neugebauer's approach), and both values agree up to average deviation of 0.7%.     

Cation self-diffusion and the isotope effect in Mn1−δO

Diffusion of ⁵⁴Mn in Mn_1?δO single crystals has been measured by a serial sectioning technique as a function of temperature (1000–1500°C) and deviation from stoichiometry (0.00003 < δ < 0.12). The value of m in the expression varies from about 6 at low Po₂ at all temperatures to a value approacing 2 at high Po₂ and high temperatures, thus suggesting that diffusion occurs by doubly charged vacancies at low Po₂ with increasing contributions from singly charged and neutral vacancies as Po₂ (and vacancy concentration) increases. For δ near 0.1, the values of D fall below the values extrapolated from smaller defect concentrations. The isotope effect for cation self-diffusion was measured by simultaneous diffusion of ⁵²Mn and ⁵⁴Mn in Mn_1?δO (0.0004 < δ < 0.116) at 1300 and 1500°C. The measured values of fΔK are independent of temperature within experimental error, and decrease from a value of 0.70 at low defect concentrations to 0.37 for large values of δ. The isotope-effect results suggest that diffusion occurs by single non-interacting vacancies at low defect concentrations; defect-defect interactions become important for δ ? 0.01. The defect-defect interactions may involve essentially individual defects or may result in defect clusters; the similarity between the present isotope-effect results and those for Fe_1?δ0 suggests that defect clustering plays a significant role in mass transport in Mn_1?δO at large values of δ.     

铒离子注入碳化硅的射程和退火行为研究

用300—500 keV能量的铒(Er)离子注入碳化硅(6H-SiC)晶体中,利用卢瑟福背散射技术研究了剂量为5×10¹⁵ cm^-2 的Er离子注入6H-SiC晶体的平均投影射程R_p和射程离散ΔR_p,将测出的实验值和TRIM软件得到的理论模拟值进行了比较,发现R_p的实验值与理论值符合较好,ΔR_p的实验值和理论值差别大一些 关键词： 离子注入 投影射程和射程离散 退火行为 卢瑟福背散射技术     

Birefringence of muscovite mica

Birefringence of muscovite mica (n_e−n_o) is usually calculated from the dispersion relations of the indices n_e and n_o. As small differences between relatively large experimentally-measured values, the few available data for birefringence of mica are widely distinct and sometimes contradict basic experimental facts. A different procedure is adopted in this work to measure birefringence directly as a single quantity in terms of the thicknesses of mica plates and the wavelengths at which they act as quarterwave or halfwave phase retarders. Birefringence is found to decrease gradually from −0.0040 at 420 nm to −0.0046 at 700 nm in conformity with pertinent independent experimental results.     

The low field longitudinal magnetoresistance of PdMn,PdFe and AuFe near the percolation limit

The low field longitudinal magnetoresistance, Δp/p_o, of Au + 14.5%at.Fe is measured as a function of field (- 1kG < H < 1kG), temperature (1.2K, 140K) and annealing conditions. When the sample is annealed and quenched from 950 C, the low field (～ 100 G) Δp/p_o versus H curve exhibits two sharp peaks at about 35 and 75 K respectively. The low temperature peak is associated with a spin glass transition (T_g) whereas the high temperature one would correspond to a ferromagnetic transition (T_c). The spin-glass state such as T ? T_g is characterised by a clear quadratic behavior of Δp/p_o as a function of H whereas in the ferromagnetic state (T_g < T < T_c), the magnetoresistance is completely dominated by a linear term. Quenching the sample from 550C considerably reduces the overall magnetoresistance, suppresses the linear term and transforms the double peak structure into a a single rather broad cusp of a spin-glass type. To help interpreting the above results, we also carried out low field magnetoresistance measurements on Pd + 0.2 at.%Fe, Pd + 2 at.%Mn and Pd + 10 at.%Mn at low temperatures.     

Orientational order and distribution function in nematic 1-(4-trans hexylcyclohexyl)-4-[(2-4-isothiocyanato phenyl)ethyl] benzene

The refractive indices (n _e,?n _o) and density have been measured as a function of temperature in the liquid-crystalline and liquid phases of nematic 1-(4-trans hexylcyclohexyl)-4-[(2-4-isothiocyanato phenyl)ethyl] benzene. The molecular polarizability and orientational order parameter have been computed using the Neugebauer anisotropic local field model. The distribution function f(β), and hence the higher order parameter ?P ₄?, and nematic pair-potential have been computed at different temperatures in the nematic phase.     

Joint Optimization of the Number of Pulses and the Relaxation Pause in the Combined Multiple-Pulse Spin-Locking Sequence for Detecting Explosives by NQR

The problem has been solved for the joint optimization of the number N of pulses and the relaxation pause t _p in the combined multiple-pulse spin-locking sequence, which is successfully used for detecting some explosives by nuclear quadrupole resonance (NQR). Initially, the formula is derived for the signal-to-noise ratio provided by this sequence. Using the condition that an explosive detection time T _det is constant (it is typical in practice), from this expression the set of two interrelated equations is obtained for optimum values of N and t _p, which provide the maximum signal-to-noise ratio. These values are determined by both effective transverse T _2e and longitudinal T ₁ relaxation times and sequence parameters, and do not depend on the number m of sequence repetitions. The m value is calculated as the quotient of T _det by the duration of the onefold sequence with optimum values of N and t _p. This set of equations is shown to be mutually compatible at all values of sequence parameters and relaxation times T ₁ and T _2e, which occur in actual practice. The results of the experiments, which have been carried out on cyclotrimethylene trinitramine (RDX) at a ¹⁴N NQR frequency of 3.41 MHz and temperatures of 26 and −3°C, are in good agreement with the theoretical ones.     

Complete basis set,hybrid‐DFT study and NBO interpretations of conformational behaviors of trans‐2,3‐ and trans‐2,5‐dihalo‐1,4‐dithianes

The conformational behaviors of trans‐2,3‐dihalo‐1,4‐dithiane [halo = F ( 1 ), Cl ( 2 ), Br ( 3 )] and trans‐2,5‐dihalo‐1,4‐dithiane [halo = F ( 4 ), Cl ( 5 ), Br ( 6 )] have been analyzed by means of complete basis set CBS‐4, hybrid‐density functional theory (B3LYP/6‐311 + G**//B3LYP/6‐311 + G**) based methods, and natural bond orbital (NBO) interpretation. Both methods showed that the axial conformations of compounds 1–5 are more stable than their equatorial conformations but CBS‐4 resulted in an equatorial preference for compound 6 . The Gibbs free energy difference (G_eq?G_ax) values (i.e., ΔG_eq–ax) at 298.15 K and 1 atm between the axial and equatorial conformations decrease from compound 1 to compound 2 but increase from compound 2 to compound 3 . Also, the calculated ΔG_eq–ax values decrease from compound 4 to compound 6 . The NBO analysis of donor–acceptor (LP → σ*) interactions showed that the anomeric effect (AE) increase from compound 1 to compound 3 and also from compound 4 to compound 6 . On the other hand, the calculated dipole moment values between the axial and equatorial conformations [Δ(µ_eq?µ_ax)] decrease from compound 1 to compound 3 . The conflict between the increase of AE and the decrease of Δ(µ_eq?µ_ax) values could explain the variation of the calculated ΔG_eq–ax for compounds 1–3 . The Gibbs free energy difference values between the axial and equatorial conformations (i.e., ΔG_ax–ax and ΔG_eq–eq) of compounds 1 and 4 , 2 and 5 and also 3 and 6 have been calculated. The correlations between the AE, bond orders, pairwise steric exchange energies (PSEE), ΔG_eq–ax, ΔG_ax–ax, ΔG_eq–eq, dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–6 have been investigated. Copyright © 2010 John Wiley & Sons, Ltd.     

Ligand‐site exchange in intramolecular complexes of silicon: substituent effects

The intramolecular complexes containing coordination bonds Si←N or Si←O are distinguished for their stereochemical nonrigidity resulting in interconversion between isomers, that is, ligand‐site exchange. The influence of the substituents bound to the silicon atom on the free energies of activation for ligand exchange ΔG^≠ of specific interest is poorly understood. In this work, the literature data on substituent influence on the energies ΔG^≠ for 13 series of the complexes have been considered, using the correlation analysis. On the basis of the obedience of the energies ΔG^≠ to the linear free energy relationship, it has been established for the first time that the ΔG^≠ values depend not only on the inductive and resonance effects but also on the polarizability and steric effects of substituents. The reason for the occurrence of the polarizability effect is the appearance of excess charges on Si and N (or O) atoms as a result of intramolecular coordination consisting in the charge transfer from the donor center (N or O atom) to the acceptor one (Si atom). In some series the contribution of the polarizability or steric effect to the overall change in ΔG^≠ because of the influence of substituents is a maximum. An understanding of these effects may give a better insight into the mechanism of nucleophilic substitution, involving organoelement compounds. Copyright © 2012 John Wiley & Sons, Ltd.     

Texture and Optical Studies of the Mesophases of Cyanocyclohexyl Cyclohexanes

Optical studies have been conducted as a function of temperature on two (CCH₃ and CCH₇) of the three odd members of the homologous series of the mesogen trans, trans-4′-alkyl-bicyclohexyl-4-carbonitrite. From birefringence studies the variation of the orientational order parameter ? P₂ ? with temperature of the two members has been determined. Texture studies have been conducted to identify hitherto unidentified phases. A comparative study of the temperature dependence of the refractive indices n _e, n _o , and ? P₂ ? of all the three members CCH₃, CCH₅, CCH₇ have been presented with a view to study the effect of increasing chain length. Comparison of the experimentally obtained ? P₂ ? values has been made with theoretical values predicted by the Maier-Saupe theory.     

Diffusionstheoretische Beschreibung der Dissoziation und des Ionenhaushaltes im schwachionisierten Säulenplasma der Wasserstoffentladung. II. Makroskopische Kenngrößen der Elektronen im H/H2-Mischplasma

The results of the calculation of the energy distribution function f(U), of the transport coefficients ū, b_e, D_e, of the collision frequencies for dissociation and direct ionization and of the main energy loss rates due to elastic and inelastic collisions of the electrons with the components of the mixture are presented for a stationary and homogeneous hydrogen plasma. These calculations, based upon the Boltzmann equation for the electrons, are performed in dependence of the normalized electric field strength E/p₀ and the mixture ratio x_D in the range of 7.5 to 100 V/cm Torr for E/p₀ and for any mixture ratio.