The intermolecular potential energy functions of krypton and xenon

The intermolecular potential energy functions for krypton and xenon have been determined using new semi-inversion techniques. These techniques, which have previously been applied to the data for argon, enable information about intermolecular forces to be obtained directly from second virial coefficient and gas viscosities measurements.     

稀有气体纯质热物理性质的预测

根据量子力学和分子运动学理论,采用稀有气体的ab initio势能,分别计算了氦-4、氖、氩、氪和氙纯质在低密度时的热物理性质,包括第二维里系数,热扩散系数和热扩散因子,计算的温度范围为50—5000 K.预测结果具有较高的精度,与采用经验势能的计算结果相比,本文结果更接近实验数据和REFPROP 8.0的标准值,为相关的科学研究和工程应用提供了所需的基础数据. 关键词： ab initio势能')" href="#">ab initio势能 稀有气体 热物理性质     

The influence of intermolecular interactions on the Kerr effect in gases

Expressions are derived for the second and third Kerr virial coefficients, B _K and C _K, of spherical top molecules in terms of irreducible cluster polarizabilities, and values are calculated using the dipole-induced dipole model for argon, krypton, xenon, methane, tetrafluoromethane, neopentane and sulphur hexafluoride. For mixtures of rare gases it is shown that the collision-induced dipole moment makes a negligible contribution to B _K. The effect of the choice of intermolecular potential function on the calculated second Kerr virial coefficients is also demonstrated. It is found that the predominant contributions to C _K arise from the pair polarizability, and that the triplet polarizability is only of minor importance.     

Accurate second Kerr virial coefficient of rare gases from the state-of-the-art ab initio potentials and (hyper)polarizabilities

The second Kerr virial coefficient of rare gases is studied in this work using the best ab initio potentials and (hyper)polarizabilities in the literature. The second Kerr virial coefficient of helium-4, helium-3, neon, argon, and krypton and its polarizability component of xenon are computed by the semi-classical method together with the Padé approximant over a wide temperature range. In addition, the uncertainty of second Kerr virial coefficient is estimated from the uncertainties of the ab initio interaction-induced properties. The experimental and theoretical data in the literature is compared with our calculated values to examine the quality of this work. It is shown that our computed values in the supplementary materials are as accurate as the literature data at medium and high temperatures and are more reliable at low temperatures.     

Magnetic anisotropies of some aromatic molecules

A common method for the estimation of uncertainties introduced by surface and impurity effects into experimental measurements of virial coefficients is described. The sign and the amplitude of the second virial coefficient response to perturbation caused by adsorption of molecules on the internal surface of the vessel have been determined. It has been shown that the magnitude of the second virial coefficient distortion depends on such competing factors as adsorption-impurity perturbation parameter, mixture composition which has been corrected taking into account this perturbation, and the nature of the impurity expressed in terms of its second virial coefficient and of the solvent-impurity cross second virial coefficient. The character of the Lennard-Jones 12–6 potential parameters perturbation, caused by the adsorption-impurity effects, is determined using second virial coefficient data inversion technique. Numerical estimates are made for nitrogen, helium, argon, xenon, their binary mixtures, and also for krypton-sulphur hexafluoride gaseous mixtures.     

The second and third virial coefficients of a two-dimensional gas

Numerical values of reduced second and third virial coefficients and their temperature derivatives are reported for a two-dimensional gas, for use in interpreting adsorption isotherms of monolayers on isoenergetic substrates. Correct values of the third virial coefficient have not been available before. Examples of earlier treatments of adsorption data are given to demonstrate that values of the higher virial coefficients are essential for adequate discussions of adsorption isotherms. When these are used the high-temperature adsorption isotherms of argon on graphitized carbon black in the monolayer region are completely described in terms of the unperturbed bulk-gas parameters.     

Molar volume for mixtures of methane with krypton,argon, ethane and carbon monoxide using the ISM equation of state

In this paper, an analytical equation of state (EoS) proposed by Ihm–Song–Mason (ISM) was employed to calculate the molar volume of mixtures of methane with krypton, argon, ethane and carbon monoxide. The best available pair interaction potential energy has been used to evaluate the second virial coefficients required by the ISM EoS. The calculated values of second virial coefficients were applied to the ISM EOS to predict the molar volumes for the above mentioned mixtures. Agreement with the experiment is excellent for all systems.     

An approximate multi-property empirical isotropic interatomic pair potential for the krypton dimer

An approximate empirical isotropic interatomic potential for krypton interaction is developed by simultaneously fitting the Morse-Morse-Morse-Spline-van der Waals potential form to the pressure second virial coefficient, viscosity, thermal conductivity and depolarized interaction-induced light scattering data. Absolute zeroth and second moments of the two-and three-body spectra, the pressure third virial coefficient and isotopic thermal diffusion factor have been measured and compared with theoretical calculations using various models for the interatomic potential. The results show that it is the most accurate potential yet reported for this system. The use of the new potential in lattice sum calculations yields good results for several properties of solid krypton.     

On the second dielectric virial coefficients of methane and the inert gases

The induced quadrupole contribution to the distortion polarization term in the dielectric virial coefficient (B) has been evaluated for methane and the inert gases neon, argon, krypton and xenon. It is shown to be a substantial fraction of the experimental value of B for these systems. For argon the full ‘ classical ’ value of B is estimated by making use of a previous calculation of the classical overlap correction to the point polarizable particle model. It is shown that the classical value of B is in substantial agreement with experiment for this case.     

Monte Carlo simulations of thermodynamic properties of argon,krypton and xenon in liquid and gas state using new ab initio pair potentials

The internal energies and compressibility factors of argon, krypton and xenon have been simulated using recent state-of-the-art ab initio pair intermolecular potentials and the best semi-empirical pair potentials, and the Axilrod-Teller-Muto three-body term. The results are compared with experimental data for both sub-critical and super-critical temperatures and for densities ranging up to a 2.5 multiple of the critical density. Both the ab initio and semi-empirical results for argon are in very good agreement with the experimental ones. For krypton and xenon, the ab initio results are worse than the semi-empirical results but they are still acceptable.     

Atomic interactions in neon and helium

The first two quantum corrections to the second virial coefficients of the Smith-Thakkar potential are calculated. Parameters for neon and helium, gases in which quantum effects are important, are then determined by fitting to semiempirical dispersion coefficients and experimental second virial coefficients. Viscosity coefficients for both gases and vibrational energy level spacings for the neon dimer are calculated as independent tests of the potentials. Overall agreement with experiment is excellent for neon and moderate for helium. The previously determined parameters for argon are found to be only very slightly perturbed by the inclusion of quantum corrections in the calculated second virial coefficients.     

Obtention des bandes de cameron par photo excitation de co en matrices d'argon de krypton et de xenon

CO trapped in solid matrices of argon, krypton and xenon has been excited by 10 eV photons. Cameron bands v′=0, v″=0,1,2,3,4 are observed during the irradiation. If red shifts are observed in argon and krypton matrices, the transition in xenon shows no differences with gas phase data.     

Size estimates of nobel gas clusters by Rayleigh scattering experiments

Noble gases (argon, krypton, and xenon) are puffed into vacuum through a nozzle to produce clusters for studying laser-cluster interactions. Good estimates of the average size of the argon, krypton and xenon clusters are made by carrying out a series of Rayleigh scattering experiments. In the experiments, we have found that the scattered signal intensity varied greatly with the opening area of the pulsed valve. A new method is put forward to choose the appropriate scattered signal and measure the size of Kr cluster.     

Thermodynamics of the Stockmayer fluid in an applied field

The thermodynamic properties of the Stockmayer fluid in an applied field are studied using theory and computer simulation. Theoretical expressions for the second and third virial coefficients are obtained in terms of the dipolar coupling constant (λ, measuring the strength of dipolar interactions as compared to thermal energy) and dipole–field interaction energy (α, being proportional to the applied field strength). These expressions are tested against numerical results obtained by Mayer sampling calculations. The expression for the second virial coefficient contains terms up to λ⁴, and is found to be accurate over realistic ranges of dipole moment and temperature, and over the entire range of the applied field strength (from zero to infinity). The corresponding expression for the third virial coefficient is truncated at λ³, and is not very accurate: higher order terms are very difficult to calculate. The virial coefficients are incorporated in to a thermodynamic theory based on a logarithmic representation of the Helmholtz free energy. This theory is designed to retain the input virial coefficients, and account for some higher order terms in the sense of a resummation. The compressibility factor is obtained from the theory and compared to results from molecular dynamics simulations with a typical value λ = 1. Despite the mathematical approximations of the virial coefficients, the theory captures the effects of the applied field very well. Finally, the vapour–liquid critical parameters are determined from the theory, and compared to published simulation results; the agreement between the theory and simulations is good.     

Delta-function expansion of Mayer function with application to virial coefficients

The Mayer cluster integrals of a fluid with smooth, repulsive interactions are expanded in orders of a well-defined softness parameter. To first but not second order in softness, all virial coefficients are given by their hard-sphere forms with an effective diameter. A closed asymptotic expression is derived for the third virial coefficient which gives excellent results for the inverse power and exponential potentials.     

Emission characteristics and electron kinetic coefficients of the plasma of a transverse volume discharge initiated in a mixture of heavy inert gases with chlorine molecules

The results of studying the radiation due to argon, krypton, and xenon monochloride bands, as well as to the bands of chlorine molecules, from the plasma of a transverse Ar-Kr-Xe-Cl₂ volume discharge are reported. The working mixture of a pulse radiation source is optimized with regard to its pressure and elemental composition and parameters of an excitation system. By numerically solving the Boltzmann kinetic equation for the electron energy distribution function, the transport characteristics of plasma electrons and discharge power specific losses are found for different values of the reduced electric field strength. The plasma parameters are simulated for the quaternary mixture, which is most appropriate for a multiwave UV-VUV source. Qualitative analysis is conducted for the most important electron processes in the multicomponent plasma that govern the joint formation of argon, krypton, and xenon monochlorides in the transverse discharge.     

Thermophysical properties and collision-induced light scattering as a probe for gaseous helium interatomic potentials

Isotropic and anisotropic collision-induced light scattering spectra of helium gas at room temperature 294.5?K and at 99.6?K with the second pressure virial coefficients, second acoustic virial coefficients, viscosity and thermal conductivity have been used for deriving the empirical models of the pair-polarizability trace and anisotropy and the interaction potential. Theoretical zeroth and second moments of the binary spectra using various models for the pair-polarizabilities and interatomic potential are compared with the experimental values performed by Le Duff's group. In addition, third pressure virial coefficients, isotopic thermal factors, self diffusion coefficients, second virial dielectric constants and second Kerr coefficients calculated for these models are compared with experimental ones. The results show that these models are the most accurate models reported to date for this system.     

Molecular dynamics studies of an m-6-8 fluid

The pressure, energy and self-diffusion coefficient have been calculated for an 11-6-8 fluid using the method of molecular dynamics. A comparison with data for argon, krypton and xenon is presented. It is shown that agreement between theory and experiment for the thermodynamic properties is generally within the estimated precision of the calculated and experimental values, provided three-body and quantum corrections are included in the calculation, except when the density approaches the triple-point density. Agreement between theoretical and experimental self-diffusion coefficients is satisfactory at all densities after allowance is made for the long-time behaviour of the velocity autocorrelation function. We demonstrate that three-body forces are important in the liquid and that our estimates of such forces are very close to those suggested by Barker, Fisher and Watts.     

Transitions and level lifetimes in Ne II, III, Ar II, III, Kr II, III and Xe II

Beam-foil spectra of neon, argon, krypton, and xenon have been recorded photographically with a fast spectrograph. The particle energies ranged from 150 to 750 keV. Transitions in Ne II, III; Ar II, III; Kr II, III; and Xe II have been identified. In addition, new multiples were identified in Ne II and Xe II and a number of unidentified lines were observed in neon, argon, and krypton. Characteristic intensity decays of over 170 lines were measured, giving the mean lives of ≈ 80 levels, with an estimated error of 30 per cent. Tabulation of energy levels with similar electron configurations in neon, argon, krypton, and xenon shows a definite progression to larger mean lives as the nuclear change increases.     

Two Hard Spheres in a Spherical Pore: Exact Analytic Results in Two and Three Dimensions

The partition function and the one- and two-body distribution functions are evaluated for two hard spheres with different sizes constrained into a spherical pore. The equivalent problem for hard disks is addressed too. We establish a relation valid for any dimension between these partition functions, second virial coefficient for inhomogeneous systems in a spherical pore, and third virial coefficients for polydisperse hard spheres mixtures. Using the established relation we were able to evaluate the cluster integral b ₂(V) related with the second virial coefficient for the Hard Disc system into a circular pore. Finally, we analyse the behaviour of the obtained expressions near the maximum density.