Volumes of mixing of n-octylacetate + n-alkanes: an interpretation in terms of the Prigogine-Flory-Patterson theory

The results of measurements of molar excess volumes V^E at 303.15 K over the whole mole fraction range for eight mixtures: n-octylacetate + n-hexane; +n--heptane; + n-octane; +nn-nonane; + n-decane; +nn-dodecane; + n-tetradecane and + n-hexadecane are presented. The experimental values of V^E show a regular pattern of behaviour for the eight sets of binary mixtures. The magnitude of V^E for this class of mixtures decreases as the n-alkane chain-length decreases. In order to explain the observed behaviour, the Prigogine-Flory-Patterson theory is used to predict the total V^E and the three different contributions to V^E. Agreement between the theoretical and experimental V^E is reasonable for the eight systems     

Experimental study of a SmA*-SmC*A phase transition

We have performed a detailed experimental study of the electroclinic behaviour in the SmA* phase above a SmA*-SmC*_A phase transition. The tilt angle and polarization were measured as a function of the applied a.c. electric field, and the dielectric constant was obtained under different values of the bias field (0≤E _d.c.≤ 3 V μm^-1). In the region of linear regime, the behaviour observed for this SmA*-SmC*_A phase transition is very similar to the one previously described for SmA*-SmC* phase transitions. The experimental results obtained under high bias field are in good agreement with the predictions of the simple theoretical model considered.     

Calculations of the frequency dependences of viscosity coefficients and elastic moduli for solutions of electrolytes over broad ranges of thermodynamic parameter variations

The dynamic equations obtained earlier for the coefficients of bulk η_V(ω) and shear η_S(ω) viscosities and bulk K(ω) and shear μ(ω) elastic moduli were used to calculate these values for a certain model of solution structure in the approximation of the theory of osmotic solution properties. The interparticle interaction potential was written as the sum of the potential of hard spheres and Coulomb attraction. The corresponding thermodynamic parameter values for the density ρ, temperature, concentration C, and adiabatic bulk modulus K _S were taken from experimental works. The results of numerical calculations of the viscoelastic properties of solutions over broad ranges of thermodynamic parameter and frequency variations were plotted and tabulated. The calculation results are compared with the available experimental data. The theoretical viscoelastic properties of solutions of electrolytes were in satisfactory agreement with the published experimental data and the results of numerical experiments for classic liquids.     

On the OH torsional motion in solid pentachlorophenol

After theoretical and experimental studies, an assignment is made at 409 cm^?1 for the OH torsional vibration in solid pentachlorophenol. An optimization method is applied to calculate the V₂ torsional barrier, which provides larger values than those obtained from the conventional methods used by other authors.     

Identification of the Active Sites on Metallic MoO2−x Nano-Sea-Urchin for Atmospheric CO2 Photoreduction Under UV,Visible, and Near-Infrared Light Illumination

We report an oxygen vacancy (V_o)-rich metallic MoO_2−x nano-sea-urchin with partially occupied band, which exhibits super CO₂ (even directly from the air) photoreduction performance under UV, visible and near-infrared (NIR) light illumination. The V_o-rich MoO_2−x nano-sea-urchin displays a CH₄ evolution rate of 12.2 and 5.8 μmol g_catalyst⁻¹ h⁻¹ under full spectrum and NIR light illumination in concentrated CO₂, which is ca. 7- and 10-fold higher than the V_o-poor MoO_2−x, respectively. More interestingly, the as-developed V_o-rich MoO_2−x nano-sea-urchin can even reduce CO₂ directly from the air with a CO evolution rate of 6.5 μmol g_catalyst⁻¹ h⁻¹ under NIR light illumination. Experiments together with theoretical calculations demonstrate that the oxygen vacancy in MoO_2−x can facilitate CO₂ adsorption/activation to generate *COOH as well as the subsequent protonation of *CO towards the formation of CH₄ because of the formation of a highly stable Mo−C−O−Mo intermediate.     

FT-IR study of the properties of water in Triton N-42 inverse micelles

The distribution of free (bulk) and bound (hydration) water in Triton N-42 inverse micelles has been studied. The percent of bulk water changes from 12% to 27% when solubilization capacity* (V _s /V _o ) increases from 0.5 vol.% to 3.5 vol.%. Triton N-42 inverse micelles contain hydration water of two types: 1) water bound with hydroxyl groups and secondary-bound with ethoxy groups and 2) water primary-bound with ethoxy groups. The quantity of water of each type is calculated as a function of solubilization capacity. The polar group of the surfactant molecule is hydrated by approximately six H₂O molecules when V _s /V _o = 3.5 vol.%.     

Volume of mixtures of nonane isomers with normal nonane and normal hexadecane at 298.15 K; an interpretation in terms of the Flory—Patterson theory

Excess molar volumes of four nonane isomers mixed with normal nonane and normal hexadecane were obtained from precise density measurements over the whole mole fraction range at 298.15 K. Good agreement was found between the experimental molar excess volume and that predicted from the Flory—Patterson theory. This work shows the importance of three contributions to V^E_m, heats of mixing (i.e., X₁₂), differences in free volume and the P* effect.     

A theoretical study of the vibrational spectra,geometry and force field of thiourea

A theoretical force field for the molecular vibrations of thiourea has been determined from ab initio calculations at the Hartree-Fock level using the 3-21G* basis set. The reliability of the force field is analyzed by calculating the vibrational frequencies for the deuterated and ¹⁵N isotopomers. Frequencies calculated from the force field are utilized to critically examine the experimental assignments for thiourea and deuterated thiourea. Theoretical geometry, the calculated IR and Raman band intensifies are analyzed.     

Topological and thermodynamic investigations of molecular interactions in binary mixtures: Molar excess volumes and molar excess enthalpies

Molar excess volumes and molar excess enthalpies of butyl acetate (i) with cyclohexane or benzene or toluene or o-, m- or p-xylene (j) binary mixtures have been measured dilatometrically and calorimetrically over the entire composition range at 308.15 K. The observed data have also been analyzed in terms of graph theoretical approach. The analysis of V^E data by graph theoretical approach suggests that butyl acetate in pure state exists as associated entity and (i + j) mixtures are characterized by the presence of (i–j) molecular entity. It has further been observed that V^E and H^E values calculated by this approach agree well with the corresponding experimental values. The presence of molecular entity is further confirmed by IR study of (i + j) mixture.     

High temperature dielectric loss of h-BN at X band and its dependence on the electron structure,defects and impurities

The dielectric loss of hexagonal boron nitride (h-BN) at high temperature ranging from 291 K to 2023 K at X band is investigated by experimental and theoretical analyses. The dielectric loss is relatively low below 1273 K, nevertheless, above this temperature, much rapid increase in the dielectric loss is observed with the increase of temperature. At 2023 K, the dielectric loss is found to be 40 times more than that at room temperature. Our calculation reveals that the rapid increase in the dielectric loss from 1273 K to 1800 K is mainly contributed by the boron vacancy (V_B) defects but from that 1800 K to 2023 K is mostly caused by the hopping phenomenon of the electrons. It is also found that the reason that V_B has the smallest energy among the defect is that its electronegativiities are smaller and its bonding ability is weaker compared to other defects. And the co-existence of defects and impurities is found to enhance the conduction loss by first principle calculations, which is due to that the bond of B1 atom and N1 atom becomes weak and the jumping distance of the impurity ions is increased when V_B and Na co-doped in the structure.     

Non-empirical calculations on the electronic spectrum of butadiene

Ab initio SCF and CI calculations of the electronic spectrum of butadiene are reported which employ a gaussian basis of double zeta quality augmented by diffuse 3s and 3p functions. Good agreement is obtained with experimental details of this spectrum, both for π→π* and certain Rydberg transitions, and it is concluded that the important NV₁ and NV₂ absorption systems both involve diffuse upper states of ¹B_u symmetry.     

Controlled-potential coulometric determination of platinum in americium—platinum alloys

A controlled-potential coulometric method for the determination of platinum in americium—platinum alloys is described. Platinum in the hexachloroplatinate complex is reduced to the metal at —0.3 V vs. the saturated silver chloride electrode on a mercury pool electrode. For quantities up to 5 mg, the standard deviation was 6.4 μg.     

Evaluation of “method uncertainty” in the calibration of piston pipettes (micropipettes) using the gravimetric method in accordance with the procedure of ISO 8655-6

The gravimetric method specified by ISO 8655-6 is a standard method for calibrating piston pipettes (micropipettes). The quality of the calibration can be assessed by uncertainty evaluation, the procedure for which is described in ISO/Technical Report (TR) 20461. However, the existence of “method uncertainty” due to ambiguity in the calibration operation, which is not described in the TR, has been found in various experiments, such as the interlaboratory comparison of CCM.FF-K4.2.2011. In this report, the “method standard uncertainty” is quantified as exp(?4.51 + 0.36 ln(V ^nom/μL) + 0.05{ln(V ^nom/μL)}²) μL for a nominal volume, V ^nom, in the range from 2 μL to 10000 μL. Furthermore, the reported values in an interlaboratory comparison are confirmed to be consistent using the quantified method standard uncertainty.     

Prediction of permselectivity of nitrate and acetate ions in the electrodialysis of aqueous solutions

Electrodialysis of aqueous solutions of acetic and nitric acids encountered in the industrial practice of deacidification of raw glyoxal solutions has been carried out to investigate the permselectivity of the system. The dependence of the permselectivity coefficient τ on experimental parameters such as flow velocity (V), current density (I), concentration of anions (C_i), etc. has been evaluated. A correlation between τ and the critical parameters has been obtained. Well-known theoretical equations have been used to calculate τ at limiting current density I_lim and as I approaches zero. Calculated results are compared with observed values. Limitations of theoretical procedures when applied to a system containing a weak acid are explained.     

RepresentationT-V-x des systemes binaires a tension de vapeur non negligeable

Binary systems with non-negligible vapour pressure may be described by theT-V-x diagram. The use of the volumeV as an independent variable makes it possible to show the part played by the vapour phase in binary systems. This first part deals with the experimental connection betweenT, V andx data measured by DTA with sealed silica ampoules. As an example the eutectic composition is used: the theoretical isothermal, isochoric and isoplethal sections are presented and compared to those of some former works.     

Experimental and theoretical studies of the Bi-excited collision systems He*(23 S) + He*(23 S, 21 S) at thermal and subthermal kinetic energies

We have carried out a comprehensive experimental and theoretical investigation of the autoionizing collision systems He*(2³ S, 2¹ S) + He*(2³ S). We present high resolution electron energy spectra, obtained with a single He* beam (average relative collision energy 〈E _rel〉=1.6 meV) and with crossed He* beams (〈E _rel〉> =61 meV). The spectra show substantial structure, and under single beam conditions fast oscillations due to the interference of incoming and outgoing heavy particle waves in the entrance channels are observed. Accurate ab initio potential curves for the seven lowest He*—He*(Σ) molecular states have been obtained from a Feshbach projection scheme, and width functions for He*(2³ S) + He*(2³ S) have been derived by Stieltjes imaging. Based on these ab initio data, detailed quantum mechanical calculations of the electron spectra have been carried out and provide a thorough understanding of the experimentally observed spectral features. Good overall agreement of the calculated spectra with the experimental data is observed. The close coincidence in the positions of the experimental and theoretical peaks, especially for He*(2³ S) + He*(2³ S), underlines the reliability of the ab initio potentials. In the He*(2¹ S) + He*(2³ S) electron spectrum, the dominant peak is traced to be due to autoionization from the 2³Σ⁺ _g molecular state accessed via an avoided crossing. We also present a detailed discussion of the total ionization cross sections σ_tot and of the fraction σ_AI/σ_tot for associative ionization together with a critical comparison with previous work. The ionization probabilities for close collisions in entrance channels, from which autoionization is spin-allowed, are near unity, and therefore the absolute values and the collision energy dependence of the total cross sections simply reflect the long-range behaviour of the excited state potentials.     

High-accuracy assessment of finiteness effects for hard disks

In a recent investigation the comparison between theoretical and computer-experimental results for the finiteness effects in hard disk systems has not been entirely conclusive. Thus, we present new Monte Carlo data of high accuracy. We also discuss some aspects of experimental design as well as refined methods of error analysis. The quantity considered is the compressibility factor Z, depending on the shape of the periodic box (for given density and particle number). The reported discrepancies in V dependence are stringently substantiated, and a semi-empirical correction of the theoretical approach is proposed. The new data also revealed an unexpected discrepancy in N dependence. For this second kind of finiteness effects, we replace the usual calculation via the virial coefficients by a computer-experimental estimate.     

Phase transition and thermodynamic properties of TiN under pressure via first-principles calculations

The phase transition of TiN from the NaCl structure to the CsCl structure is investigated by the first-principles plane wave pseudopotential density functional theory method, and the thermodynamic properties of the NaCl structures are obtained through the quasi-harmonic Debye model. It is found that the pressures for transition from the NaCl structure to the CsCl structure are 364.1 GPa (for GGA) and 322.2 (for LDA) from equal enthalpies. The calculated ground state properties such as equilibrium lattice constant, bulk modulus, and its pressure derivative are in good agreement with experimental and theoretical data of others. Moreover, the dependences of the relative volume V/V ₀ on the pressure P, the Debye temperature ?? _D , and heat capacity C _V on the pressure P and temperature T, as well as the variation of the thermal expansion ?? with temperature and pressure are also successfully obtained.     

Vibrational energy transfer in near resonance due to dipole–dipole interactions

The contribution of long-range forces to the observed rates of V → V energy transfer processes has been studied. The theoretical model uses the first order perturbation approximation to generate a probability function, with the dipole–dipole perturbing potential as given by Margenau: V_if = [(1/6)^1/2_{μ1 · μ2}]R^?3. The probability function derived is shown to be a strong function of the energy mismatch between the IR bands of the colliding molecules. The calculation emphasizes the importance of rotational state population effects, the most important J states being those which minimize the energy mismatch. A complete analysis of energy transfer between CO(v) and COS(000) where v = 1,2, ? 13 is presented. The calculation reveals the importance of combination bands in the energy transfer mechanism of polyatomics. The temperature dependence for near-resonant processes is also studied and the importance of the V → R energy transfer leads to the classification of ω₀ (band-center energy mismatch) into three categories small, medium, and large, according to the temperature dependence that the corresponding processes exhibit. The predictions of the theoretical model are compared to experimental data for the same system.