Binary Rare Gas Mixtures Research Articles

Absorption spectra of e-beam-excited Ne, Ar, and Kr, pure and in binary mixtures

A technique using the broadband emission of a laser plume as probe radiation is applied to record UV-visible (190-510 nm) absorption spectra of Ne, Ar, and Kr, pure and in binary mixtures under moderate e-beam excitation up to 1 MW/cm(3). In all the rare gases and mixtures, the absorption spectra show continuum related to Rg(2) (+) homonuclear ions [peaking at λ∼285, 295, and 320 nm in Ne, Ar, and Kr(Ar/Kr), respectively] and a number of atomic lines related mainly to Rg(∗)(ms) levels, where m is the lowest principal quantum number of the valence electron. In argon, a continuum related to Ar(2) (∗) (λ∼325 nm) is also recorded. There are also trains of narrow bands corresponding to Rg(2) (∗)(npπ (3)Π(g))←Rg(2) (∗)(msσ (3)Σ(u) (+)) transitions. All the spectral features mentioned above were reported in literature but have never been observed simultaneously. Although charge transfer to a homonuclear ion of the heavier additive is commonly believed to dominate in binary rare-gas mixtures, it is found in this study that in Ne/Kr mixture, the charge is finally transferred from the buffer gas Ne(2) (+) ion not to Kr(2) (+) but to heteronuclear NeKr(+) ion.

Opticheskie spektry binarnykh smesei inertnykh gazov

Opticheskie spektry binarnykh smesei inertnykh gazov

Ion mobilities in Xe/Ne and other rare-gas mixtures.

The ion mobility or drift velocity data important for modeling glow discharges in rare gas mixtures are not generally available, nor are the ion-neutral scattering cross sections needed to calculate these data. In this paper we propose a set of cross sections for Xe+ and Ne+ collisions with Xe and Ne atoms. Ion mobilities at 300 K calculated using this cross section set in a Monte Carlo simulation are reported for reduced field strengths, E/N, up to 1500 x 10(-21) V m(2), in pure gases and in Xe/Ne mixtures containing 5% and 20% Xe/Ne, which are mixtures of interest for plasma display panels (PDPs). The calculated Xe+ mobilities depend strongly on the mixture composition, but the Ne+ mobility varies only slightly with increasing Xe in the mixture over the range studied here. The mobilities in pure gases compare well with available experimental values, and mobilities in gas mixtures at low E/N compare well with our recent measurements which will be published separately. Results from these calculations of ion mobilities are used to evaluate the predictions of Blanc's law and of the mixture rule proposed by Mason and Hahn [Phys. Rev. A 5, 438 (1972)] for determining the ion mobilities in mixtures from a knowledge of the mobilities in each of the pure gases. The mixture rule of Mason and Hahn is accurate to better than 10% at high field strengths over a wide range of conditions of interest for modeling PDPs. We conclude that a good estimate of ion mobilities at high E/N in Xe/Ne and other binary rare gas mixtures can be obtained using this mixture rule combined with known values of mobilities in parent gases and with the Langevin form for mobility of rare gas ions ion in other gases. This conclusion is supported by results in Ar/Ne mixtures which are also presented here.

VUV emission spectra from binary rare gas mixtures near the resonance lines of Xe I and Kr I

Emission spectra of Xe–X (X = He, Ne, Ar and Kr) and of Kr–Y (Y = He, Ne and Ar) mixtures with low concentrations of the heavier gases (0.1–1%) and moderate total pressures (50–200 hPa) have been recorded near each of the two resonance lines of Xe and Kr in DC glow capillary discharges. The recorded intense emissions have narrow spectral profiles with FWHM of about 0.1 nm. The profiles are very similar in shape to profiles of known high resolution absorption spectra recorded at comparable gas pressures. A tentative identification of the emission structures is given, which involves transitions in heteronuclear molecules and quasimolecules between weakly-bound states.

Inadequacy of the Lorentz-Berthelot combining rules for accurate predictions of equilibrium properties by molecular simulation

Though molecular beam experiments have revealed deficiencies in the Lorentz-Berthelot combining rules, these rules are still used widely to parametrize effective pair potential models or to calculate the thermodynamic properties of mixtures. Gibbs ensemble Monte Carlo and isothermal isobaric Monte Carlo simulations were used to compute the liquid-vapour phase equilibria and the liquid properties of binary mixtures of rare gases modelled by effective pair potentials. Three sets of simple combining rules were tested in this work: the commonly used Lorentz-Berthelot rules, the Kong rules (Kong, J., 1973, J. chem. Phys., 59, 2464) and the Waldman-Hagler rules (Waldman, M., and Hagler, A. T., 1993, J. comput. Chem., 14, 1077). These three sets of rules do not require any additional parameter. It is shown that: (1) the choice of a set of combining rules has a significant effect on the thermodynamic properties, (2) using the Lorentz-Berthelot rules yields significant deviations from experiment and (3) the Kong rules provide a much better description of the mixture properties both for coexistence curves and liquid properties. We therefore recommend the use of the Kong rules instead of the Lorentz-Berthelot when parametrizing potential models.

Radiation trapping of the3P1−1S0resonant transitions of xenon and krypton in Xe-Kr, Xe-Ar, and Kr-Ar mixtures: Kinetic analysis and determination of the van der Waals broadening coefficients

This work concerns radiation trapping of the 123-nm krypton and 147-nm xenon lines, in the presence of a lighter rare gas, as well as the study of the decay processes of the relevant resonant states due to inelastic collisions. It deals with Kr-Ar, Xe-Kr, and Xe-Ar mixtures. Pulsed, brief selective excitation of the $\mathrm{Xe}{(}^{3}{P}_{1})$ or $\mathrm{Kr}{(}^{3}{P}_{1})$ resonant states by three-photon absorption was achieved by means of a tunable dye laser. Spectral and temporal analysis was then performed. The time resolved luminescence, filtered in the vacuum ultraviolet region, obeys a decay law described by the sum of two exponential terms which are attributed to the deexcitation of the ${}^{3}{P}_{1}$ and ${}^{3}{P}_{2}$ states. The decay constants are estimated by the maximum likelihood method applied to a Poisson statistical law. In order to correctly determine the collision rate constants, it is important to account for variations of the apparent lifetime according to the gas concentration. Analysis of both systematic experimental errors and statistical errors leads to a good estimation of the accuracy of the results obtained. For each mixture, the variation of the time constants as a function of partial pressures allows a determination of the resonance broadening coefficient and van der Waals broadening coefficient of the transition studied, as well as the two- and three-body inelastic collision rates relative to the ${}^{3}{P}_{1}$ and ${}^{3}{P}_{2}$ states. There exists no energy transfer between the two gases. For binary rare-gas mixtures, where only the heavier gas is excited, homonuclear and heteronuclear three-body reactions account for the decay of the ${}^{3}{P}_{1}$ state. Nevertheless, for the ${}^{3}{P}_{2}$ state we observe both two- and three-body collisions. In order to simulate resonance radiation trapping, a numerical method based upon Monte Carlo techniques was used. Calculations were first performed and validated for an infinite cylinder. The difference between calculation and experiment was less than 1%. Then the program was adapted to our real experimental conditions and applied to the binary mixtures studied. A good agreement was found between experiments and calculations. Furthermore, our program allows us to obtain information not easily obtained experimentally.

Thermal mobilities of electrons in binary rare gas mixtures

The mobility of electrons in binary mixtures of the inert gases is calculated versus mole fraction for different electric field strengths. The deviations from the linear variation of the reciprocal of the mobility of the mixture with mole fraction, that is from Blanc's law, is determined and interpreted in detail. Very large deviations from the linear behaviour were calculated for several binary mixtures at specific electric field strengths, in particular for HeXe mixtures. An interesting effect was observed whereby the electron mobility in HeXe mixtures, for particular compositions and electric field strength could be greater than in pure He or less than in pure Xe. The results of this study suggest that the experimental measurements of the electron mobility in these mixtures could be used to refine the electron-atom momentum transfer cross sections.

High-energy electron distribution in electron beam excited Ar/Kr and Ne/Xe mixtures

The electron energy distribution in electron beam (e beam) excited Ar/Kr and Ne/Xe gas mixtures is examined in detail. The binary rare-gas mixtures are similar to those used in excimer lasers. Cooling processes for the secondary electrons generated in the gas mixture plasma by the e beam are calculated using a reduced Boltzmann equation in which elastic and electron-electron collisions for electron energy distributions above the first excitation threshold of the rare gas are ignored. During the calculations for the Ar/Kr and Ne/Xe mixtures, all electron-related reactions and the interaction between the two different rare gases in the mixture are simultaneously considered. The high-energy secondary electrons produce a steady-state distribution within a very short time; however, it is found that the distribution is not Maxwellian. W values [eV/electron-ion pair] and yields of rare-gas excited states calculated from the steady-state high-energy electron distribution show a dependence on the mixture composition, especially for mixtures with low concentrations of the minor rare gas. This implies that the practice in excimer kinetics models of using the W values determined from pure rare gases is not entirely accurate.

Vacuum ultraviolet absorption spectra of binary rare gas mixtures and the properties of heteronuclear rare gas van der Waals molecules

Vacuum ultraviolet absorption spectra of binary rare gas mixtures Xe/X (X=He, Ne, Ar, or Kr) and Kr/Y (Y=He, Ne, Ar, or Xe) near each of the first two resonance lines of Xe i and Kr i, respectively, have been photographed at high resolution by a 6.65 m spectrograph with a rare gas continuum as background source. The overall formation of spectral features near a resonance line is predominantly towards short wavelengths, and the degree to which discrete bands form near a resonance line generally increases with increasing atomic weight of X or Y. Partial interpretations of the absorption spectra are given in terms of transitions within the heteronuclear rare gas van der Waals molecule XeX or KrY, from the bound ground electronic state (Ω=0) to bound or free excited electronic states (Ω=0,1). Bound excited electronic states are found for KrXe near the first resonance levels of Xe i and Kr i, and for KrXe and ArXe near the second resonance level of Xe i.

Thermal Conductivity of Binary Mixtures of Rare Gases in the Temperature Range 400–2500 K

By utilizing the recent experimental data on pure gases, thermal conductivity of six equimolar binary rare gas mixtures has been computed from Wassiljewa's expression in the temperature range 400–2500 K. The values of φij determined with the help of the expression due to Mason and Saxena are also listed as function of temperature.

Induced far-infrared absorption in rare-gas mixtures

Translational collision-induced absorption spectra of five binary rare gas mixtures have been recorded at various densities. The experimental procedure with special control requirements is described first. The binary feature of the absorption is shown to be valid over a large density range. For this particular situation, absorption coefficients and integrated intensity values have been expressed in terms of the product of density units. Finally, a comparison between experimental and theoretical results is discussed.

An electron-diffraction study of thin films of the binary mixtures of rare gases

The structures of Ar–Kr, Kr–Xe, and Ar–Xe gas mixtures were studied in the temperature range from 6°K up to the sublimation temperature of the components by transmission electron-diffraction. A phase separation in the Ar–Kr and Kr–Ne systems was not observed, and the concentration dependence of the lattice parameters was found to be in agreement with the results predicted according to Prigogine's “average potential theory” for binary solutions. In the case of Ar–Xe the solubility was observed only in small concentration ranges (0 to 11 and 80 to 100 mol%Xe) while outside this range a phase separation was observed accompanied by the formation of a highly dispersed phase. An effect of the thickness of the deposit on the mutual solubility of the components of the investigated systems was not found in our experiments. Die Strukturen von Ar–Kr-, Kr–Xe- und Ar–Xe-Gasgemischen wurden im Temperaturbereich von 6°K bis zur Sublimationstemperatur der Komponenten mittels Transmissions-Elektronenmikroskopie untersucht. In den Systemen Ar–Kr und Kr–Xe wurde keine Phasentrennung beobachtet; die Konzentrationsabhangigkeit der Gitterparameter stimmt mit den Vorhersagen gemas der Prigoginschen Theorie des “mittleren Potentials” fur binare Losungen uberein. Fur Ar–Xe wurde Loslichkeit nur in schmalen Konzentrationsbereichen (0 bis 11 und 80 bis 100 Mol%Xe) beobachtet, wahrend auserhalb dieses Gebietes Phasentrennung verknupft mit der Bildung einer hochdispersen Phase auftritt. Ein Einflus der Dicke der Ablagerung auf die gegenseitige Loslichkeit der Komponenten der untersuchten Systeme wurde in unseren Experimenten nicht gefunden.

Pressure shifts of Cs absorption lines due to binary mixtures of rare gases

The pressure shifts of high member lines of Cs due to binary mixtures of He and Ar, Kr or Xe, with proper mixing ratios, are shown to be approximately zero. This is in agreement with the author's collective perturbation model.