Transport and relaxation properties of isotopomeric hydrogen–helium binary mixtures. I. H2–He mixtures

An extensive comparison has been carried out between calculated and measured bulk properties of H₂–helium mixtures. Detailed comparisons are presented for the interaction second virial coefficient, binary diffusion, mixture shear viscosity and thermal conductivity, rotational relaxation, thermal diffusion field-effects, collision broadening of the depolarized Rayleigh light scattering spectrum, and flow birefringence. Scattering calculations have been carried out for the ab initio potential energy surfaces obtained by Tao (1994, J. chem. Phys., 100, 4947) and Schaefer and Köhler (1985, Physica A, 129, 469). The values for the various bulk gas properties calculated from these two potential surfaces are generally found to lie within or near the experimental uncertainties.     

Transport properties of H–N2 mixtures

Transport coefficients (shear viscosity, volume viscosity, thermal conductivity, and mass and thermal diffusion coefficients) of H–N₂ mixtures in the dilute-gas limit have been calculated from the intermolecular potential in the temperature range 300–2000K using the classical trajectory method. The intermediate results pertaining to H–N₂ binary interactions are reported, mainly in terms of cross-section ratios. Cross-sections evaluated with the Mason–Monchick approximation yield very good results for this system, the largest deviations, about 2.5%, being observed for the thermal diffusion coefficient. The accuracy here of this approximation can primarily be attributed to a light H atom and a weakly non-spherical potential resulting in a high rotational collision number. Furthermore, we investigate to which H–N₂ cross-sections and their ratios the values of the mixture transport coefficients are most sensitive. Our results indicate that, for some cross-section ratios, reliance on universal correlations at high temperatures, often used in flame codes, can induce sizeable errors in the thermal conductivity coefficient and especially in the thermal diffusion coefficients. We also observed that the volume viscosity is particularly sensitive to the value of the cross-section for internal energy relaxation in H–N₂ collisions.     

Dielectric relaxation and hydrogen bonding studies of 1,3-propanediol–dioxane mixtures using time domain reflectometry technique

The complex permittivity, static dielectric constant and relaxation time for 1,3-propanediol, 1,4-dioxane and their mixtures have been studied using time domain reflectometry (TDR). The excess permittivity, excess inverse relaxation time and Kirkwood correlation factor have also been determined at various concentrations of dioxane. Hydrogen bonded theory was applied to compute the correlation terms for the mixtures. The Bruggeman model for the nonlinear case has been fitted to the dielectric data for mixtures.     

Anisotropic relaxation time T′2 of solid 3He

This paper investigates an anisotropy of the adiabatic relaxation time T ₂′ for single crystalline bcc ³He. No difference in the calculation of T ₁(0) was revealed between the nearest-neighbor anti-ferromagnetic Heisenberg model and the multiple exchange model. However, we may distinguish these two models by the anisotropy of the adiabatic relaxation time T ₂′. The results presented in this paper are compared with experimental observations.     

Ab initio potential energy curve for the helium atom pair and thermophysical properties of dilute helium gas. I. Helium–helium interatomic potential

A helium–helium interatomic potential energy curve was determined from quantum-mechanical ab initio calculations. Very large atom-centred basis sets including a newly developed d-aug-cc-pV8Z basis set supplemented with bond functions and ab initio methods up to full CI were applied. The aug-cc-pV7Z basis set of Gdanitz (J. Chem. Phys. 113, 5145 (2000)) was modified to be more consistent with the aug-cc-pV5Z and aug-cc-pV6Z basis sets. The diagonal Born–Oppenheimer corrections as well as corrections for relativistic effects were also calculated. A new analytical representation of the interatomic potential energy was fitted to the ab initio calculated values. In a following paper this potential model will be used in the framework of quantum-statistical mechanics and of the corresponding kinetic theory to calculate the most important thermophysical properties of helium governed by two-body and three-body interactions.     

Stability of the H2–(He,Ne, Ar) fluid mixtures

A theory of mixtures based on a statistical mechanical perturbation scheme is used to compute the excess free energy of mixing, the excess entropy of mixing and the concentration fluctuations in the long wavelength limit as functions of composition (c) over a wide range of temperature (T = 150 to 350 K) and pressure (p = 10 MPa to 10 GPa). This has been utilized to investigate the effects of c, T and p on the solubility of H₂ (the first element of the periodic table) to He, Ne and Ar (the first three elements of the last group) and the thermodynamic stability of the mixture. The long-range correlations among the constituent species are included through the double Yukawa potential which acts as a perturbation to the hard sphere reference mixture. The non-additivity of the potentials of the constituent species is linked to the second virial coefficients which can be determined from the experimental data. Necessary corrections to the equation of state for dimerisation of H₂ molecule and quantum effects are included. At a given T = 150 K and p = 100 MPa, H₂–Ar mixture exhibits greater thermodynamic stability than H₂–Ne and H₂–Ar.     

Theoretical Study of the Electronic and Transport Properties of Lateral 2D–1D–2D Graphene–CNT–Graphene Structures

JETP Letters - The electronic and transport properties of new hybrid 2D–1D–2D structures of carbon atoms, which are graphene sheets continuously connected through a fragment of a...     

CARS difference spectroscopy. II—Determination of small frequency shifts and band width changes in binary mixtures

The experimental verification of CARS difference spectroscopy (CARS-DS) is presented and its application to binary mixtures is shown. The experimental set-up allows the simultaneous measurement of CARS spectra of two different samples under identical conditions. It is shown how the method can be used for the accurate determination of small frequency shifts and band width changes in liquid mixtures. The experimental spectra obtained were analysed by their numerical simulation using a least-squares fitting routine. As examples, experimental results for chloroform–deuterochloroform isotopic mixtures and binary mixtures of benzene and toluene of different concentrations are presented. In both cases frequency shifts and changes in the band width were observed which exhibit an almost linear dependence on the mole fraction of the probe species.     

The Hugoniot equation of state of the fluid He+D2 mixtures

The fluid variational theory and effective one-component model have been used to calculate the Hugoniot equation of state (EOS) of fluid He, D2, and He+D2 mixtures with different He:D2 compositions under high pressures and temperatures. An examination of the confidence of above computation is performed by comparing experiment and calculation, in which the similar calculation procedure used for He+D2 is adopted, of He and D2 each, since no experimental data are available to conduct this kind of comparison. Good agreement in both comparisons is found. This fact may be looked as if an indirect positive verification of calculation procedure used here at least in the pressure and temperature domain covered by the experimental data of He and D2 used for comparison, numerically nearly up to 35 GPa and 105K.     

Measurement of the Soret,diffusion, and thermal diffusion coefficients of three binary organic benchmark mixtures and of ethanol–water mixtures using a beam deflection technique

We have measured the Soret (S _T ), diffusion (D), and thermal diffusion (D _T ) coefficients of three binary mixtures of dodecane (DD), isobutylbenzene (IB) and 1,2,3,4-tetrahydronaphthalene (TH) for a concentration of 50 wt% at a temperature of 25°C by means of an optical beam deflection cell. This relevant experimental technique was still missing from a recent benchmark campaign for the measurement of the Soret effect. The measured coefficients agree to within a few percent (10% for S _T , D of TH/IB) with the proposed benchmark values. A detailed analysis of the measurement process of the beam deflection cell, which allows for an elegant extension to include temperature gradients within the windows, is given, and improved benchmark values are suggested. In addition, ethanol–water mixtures have been investigated very carefully over a broad concentration and temperature range. Comparison with data of Kolodner and Wiegand gives a generally good agreement with some systematic deviations. Contrary to theoretical predictions, we have not been able to identify a second sign change of S _T at high ethanol concentrations.     

Near-Threshold Low Rydberg Depletion Spectroscopy of H2, D2, and HD

Using high-resolution depletion spectroscopy, we have experimentally studied the physics of near-threshold low Rydberg states of all three stable isotopic variants of molecular hydrogen. The experiments were required to calibrate the absolute wavelength, including several transitions from the EF (v = 0) and EF (v = 6 or v = 9) to the same low-n Rydberg states. The measurements have been performed for several initial rotational levels in all three stable isotopic variants. Transitions to very high vibrational levels of the B, Bt, and C states have been measured with accuracy 0.002cm^-1. The pulsed amplifier perturbations were also measured by opticalhe terodyne methods.     

Thermal diffusion in binary mixtures containing molecular gases. III. The temperature dependence of αT

A recent expression for the thermal diffusion factor α_T for binary atom-molecule mixtures, which includes a full range of inelastic collisional contributions [McCourt, F. R. W., 2003, Molec. Phys., 101, 2181] has been utilized to calculate its temperature dependence for equimolar N₂-He, Ne, Ar mixtures and for an equimolar CO₂-Ar mixture. Accurate classical trajectory values for the effective cross-sections entering into the expression for α_T, obtained for the most reliable potential energy surfaces available, have been employed in the calculations. Good agreement has been attained with experiment for all four binary mixtures, including the decrease of α_T with increase in temperature observed for CO₂-Ar mixtures, heretofore considered to be anomalous.     

Dielectric loss,conductivity relaxation process and magnetic properties of Mg substituted Ni–Cu ferrites

The dielectric properties, dc and ac electrical resistivities of Mg substituted Ni–Cu ferrites with general formula Ni_0.5Cu_0.5−xMg_xFe₂O₄ (0.0≤x≤0.5) have been investigated as a function of frequency, temperature and composition. ac resistivity of all the samples decreases with increase in the frequency exhibiting normal ferrimagnetic behavior. The frequency dependence of dielectric loss tangent showed a maximum in between 10 Hz and 1 kHz in all the ferrites. The conductivity relaxation of the charge carriers was examined using the electrical modulus formulism, and the results indicate the presence of the non-Debye type of relaxation in the prepared ferrites. Similar values of activation energies for dc conduction and for conductivity relaxation reveal that the mechanism of electrical conduction and dielectric polarization is the same in these ferrites. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates that the distribution of relaxation time is temperature independent. The saturation magnetization and coercivity as calculated from the hysteresis loop measurement show striking dependence on composition.     

Infrared spectra of acetylene–water complexes: C2D2–H2O,C2D2–HDO,and C2D2–D2O

Infrared spectra of C₂D₂–water complexes are studied in the 4.1 μm region of the C₂D₂ ν₃ fundamental band using a tunable diode laser source to probe a pulsed supersonic slit jet. Relatively large vibrational red shifts (?27.7 to ?28.0 cm^?1) are observed which are more easily interpretable than for the analogous C₂H₂ vibration thanks to the absence of Fermi resonance effects for C₂D₂. Noticeable homogeneous line broadening leads to estimates of upper state predissociation lifetimes of about 0.5, 0.9 and 1.1 ns for C₂D₂–H₂O, –HDO, and –D₂O, respectively. Transitions involving K_a = 0 and 1 levels are observed for C₂D₂–HDO, but there is a puzzling absence of K_a = 1 for C₂D₂–H₂O and C₂D₂–D₂O.     

Molecular Dynamics Study of gases H2,D2 and T2

The classical Molecular dynamics simulation has been used to study the equation of state of gas H2,D2 and T2.It has also been investigated that the isotope mass affects on the accuracy of equation of state.Our calculated Iesults show that the classical effect is principal and the isotope mass effects on the equation of state are obvious for the much light gases.At the same time,some useful theoretical data of equation of state for these gases have been provided.It is found that the classical simulation is still effective to the quantum gas.However,the quantum mechanics simulation and the improvement of intermolecular interaction potential are necessary if more accurate computational results are expected.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Interaction potentials,spectroscopy and transport properties of RG+–He (RG=Ar–Rn)

High-level ab initio potential energy curves are calculated for the RG⁺–He complexes (RG=Ar–Rn). RCCSD(T) calculations are employed with large basis sets, and taking account of spin–orbit coupling. The calculated spectroscopic parameters are compared with experimentally determined values, with other high-level ab initio results, and with results from potentials that were obtained by fitting to experimental data. The gas-phase mobilities of RG⁺ ions in He are calculated from our potentials and compared, graphically and statistically, with the experimental mobilities as a function of E/n ₀ at several temperatures. We conclude that more precise experimental data are required in order to discriminate between potentials with more certainty. In addition, we discuss previously reported, unexpectedly large drops in experimental mobility values for RG⁺ in He at 4.35 K as E/n ₀ → 0.