Monatomic gas

About: Monatomic gas is a research topic. Over the lifetime, 1106 publications have been published within this topic receiving 23987 citations.

Rarefied Gas Dynamics

Abstract: Collisional Processes.- Analytical Formulae for Cross Sections and Rate Constants of Elementary Processes in Gases.- Relaxation of Velocity Distribution of Electrons Cooled (Heated) By Rotational Excitation (De-Excitation) Of N2.- Effects of the Initial Molecular States in a High-Energy Scattering of Molecular Beams.- Differential Cross Sections for Ion-Pair Formation with Selection of the Exit Channel.- Low-temperature Viscosity Cross Sections Measured in a Supersonic Argon Beam II.- Excited Oxygen Iodine Kinetic Studies.- Determination of Antisymmetric Mode Energy of CO2 Injected into a Supersonic Nitrogen Flow.- Molecular Beams.- Where are we going with molecular beams?.- Cesium Vapor Jettarget Produced With a Supersonic Nozzle.- Basic Features of the Generation and Diagnostics of Atomic Hydrogen Beams in the Ground and Metastable 22S1/2-States to Determine the Fundamental Physical Constants.- Optical Pumping Of Metastable Neon Atoms in A Weak Magnetic Field.- CO2-Laser Excitation of a Molecular Beam Monitored By Spontaneous Raman Effect.- Time-of-Flight and Electron Beam Fluorescence Diagnostics: Optimal Experimental Designs.- Molecular Beam Time-of-Flight Measurements in A Nearly Freejet Expansion of High Temperature Gas Produced By a Shock Tube.- Electron Beam Diagnostics.- Electron-Beam Diagnostics of High Temperature Rarefied Gas Flows.- Excitation Models Used in the Electron Beam Fluorescence Technique.- Electron - Beam Diagnostics in Nitrogen Multiquantum Rotational Transitions.- Free Jets, Nonequilibrium Expansions.- Free Jet as an Object of Nonequilibrium Processes Investigation.- State Dependent Angular Distributions of Na2 Molecules in a Na/Na2 Free Jet Expansion.- Molecular Beam Time-of-Flight Measurements and Moment Method Calculations of Translational Relaxation in Highly Heated Free Jets of Monatomic Gas Mixtures.- Rovibrational State Population Distributions of CO (v ? 4, J ? 10) In Highly Heated Supersonic Free Jets of CO-N2 Mixtures.- Free Jet Expansion with A Strong Condensation Effect.- Measured Densities in UF6 Free Jets.- Rotational Relaxation of NO in Seeded, Pulsed Nozzle Beams.- The Free-Jet Expansion from a Capillary Source.- Rotational Relaxation in High Temperature Jets of Nitrogen.- Translational Nonequilibrium in a Free Jet Expansion of a Binary Gas Mixture.- Laser Induced Fluorescence Study of Free Jet Expansions.- Jet-Surface Interactions.- Experimental Study of Plume Impingement and Heating Effect on Ariane's Payload.- The Interaction of a Jet Exhausting from a Body with a Supersonic Free Flow of a Rarefied Gas.- Modelling Control Thruster Plume Flow and Impingement.- Impingement of a Supersonic, Underexpanded Rarefied Jet upon a Flat Plate.- Some Peculiarities of Power and Heat Interaction of a Low Density Highly Underexpanded Jet with a Flat Plate.- Condensation in Flows.- Nonequilibrium Condensation in Free Jets.- Condensation and Vapour-Liquid Interaction in a Reflected Shock Region.- Homogeneous and Heterogeneous Condensation of Nitrogen in Transonic Flow.- Investigation of Nonequilibrium Homogeneous Gas Condensation.- The Peculiarities of Condensation Process in Conical Nozzle and in Free Jet Behind it.- Investigation of Nonequilibrium Argon Condensation In Supersonic Jet By Mass-Spectrometry, Electron Diffraction and VUV Emission Spectroscopy.- Clusters and Nucleation Kinetics.- The Microscopic Theory of Clustering and Nucleation.- Kinetics of Cluster Formation and Growth in the Process of Isothermal Condensation.- Relaxation Processes in a Molecular Dynamic Model of Cluster from the Lennard-Jones Particles.- Quantum-Chemical Study Of Processes With Cluster Isomerism.- The Homogeneous Nucleation at the Continuously Changing Temperature and Vapour Concentration.- Molecular Clusters as Heterogeneous Condensation Nuclei.- Experiments with Clusters.- The Photochemistry of Small van der Waals Molecules as Studied by Laser Spectroscopy in Supersonic Free Jets.- Diagnostics of Clusters in Molecular Beams.- Experimental Studies of Water-Aerosol Explosive Vaporization.- Laser Probing of Cluster Formation and Dissociation in Molecular Beams.- Free Molecule Drag on Helium Clusters.- Vibrational Relaxation Kinetics in a Two-Phase Gas-Cluster System.- Gas-Particle Flows.- Long-Range Attraction in the Collisions of Free-Molecular and Transition Regime Aerosol Particles.- Nonequilibrium Statistical Theory of Dispersed Systems.- The Mechanism of Strong Electric Field Effect on the Dispersed Media in the Rarefied Gas.- Generation of High-Speed Aerosol Beams By Laval Nozzles.- Kinetic Model of a Gas Suspension.- Gas Mixtures.- Kinetic Phenomena in the Rarefied Gas Mixtures Flowing Through Channels.- On the Discrete Boltzmann Equation for Binary Gas Mixtures.- Peculiarities and Applicability Conditions of Macroscopic Description of Disparate Molecular Masses Mixture Motion.- Numerical Solution of the Boltzmann Kinetic Equation for the Binary Gas Mixture.- Species Isotope Separation.- Gas or Isotope Separation by Injection into Light Gas Flow.- Molecular Diffusion Through a Fine-Pored Filter Versus Resonante IR-Radiation Intensity.- On Limiting Situations of Gas Dynamic Separation.- A Study of Reverse Leaks.- Investigation of Nonequilibrium Effects in Separation Nozzles by Monte-Carlo Simulation.- Separation of Binary Gas Mixtures at their Effusion through a Capillary and a Nuclear Filler into Vacuum.- Ionized Gases.- Effects of Nonideality in Quantum Kinetic Theory.- Molecular Mass and Heat Transfer of Chemical Equilibrium Multicomponent Partially Ionized Gases in Electromagnetic Field.- Spectroscopic Study of a Plasma Flow along the Stagnation Streamline of a Blunt Body.- On Model Kinetic Operators and Corresponding Langevin Sources for a Non-Equilibrium Plasma.- Related Fields.- Rarefied Gas Dynamics as Related to Controlled Thermonuclear Fusion.- Vacuum Ejectors with Appreciably Uneven Flows in Channels at Low Reynolds Numbers.- Simulation of the Process of the Cosmic Body Formation.

Virial shocks in galactic haloes

Abstract: We investigate the conditions for the existence of an expanding virial shock in the gas falling within a spherical dark matter halo. The shock relies on pressure support by the shock-heated gas behind it. When the radiative cooling is efficient compared with the infall rate, the post-shock gas becomes unstable; it collapses inwards and cannot support the shock. We find for a monatomic gas that the shock is stable when the post-shock pressure and density obey γ e f f ≡ (d In P/dt)/(d In p/dt) > 10/7. When expressed in terms of the pre-shock gas properties at radius r it reads as ρrΛ(T)/u 3 < 0.0126, where p is the gas density, u is the infall velocity and A(T) is the cooling function, with the post-shock temperature T u 2 . This result is confirmed by hydrodynamical simulations, using an accurate spheri-symmetric Lagrangian code. When the stability analysis is applied in cosmology, we find that a virial shock does not develop in most haloes that form before z ∼ 2, and it never forms in haloes less massive than a few 10 1 1 M O .. In such haloes, the infalling gas is not heated to the virial temperature until it hits the disc, thus avoiding the cooling-dominated quasi-static contraction phase. The direct collapse of the cold gas into the disc should have non-trivial effects on the star formation rate and on outflows. The soft X-ray produced by the shock-heated gas in the disc is expected to ionize the dense disc environment, and the subsequent recombination would result in a high flux of La emission. This may explain both the puzzling low flux of soft X-ray background and the La emitters observed at high redshift.

A stable argon compound

Abstract: The noble gases have a particularly stable electronic configuration, comprising fully filled s and p valence orbitals. This makes these elements relatively non-reactive, and they exist at room temperature as monatomic gases. Pauling predicted1 in 1933 that the heavier noble gases, whose valence electrons are screened by core electrons and thus less strongly bound, could form stable molecules. This prediction was verified in 1962 by the preparation of xenon hexafluoroplatinate, XePtF6, the first compound to contain a noble-gas atom2,3. Since then, a range of different compounds containing radon, xenon and krypton have been theoretically anticipated and prepared4,5,6,7,8. Although the lighter noble gases neon, helium and argon are also expected to be reactive under suitable conditions9,10, they remain the last three long-lived elements of the periodic table for which no stable compound is known. Here we report that the photolysis of hydrogen fluoride in a solid argon matrix leads to the formation of argon fluorohydride (HArF), which we have identified by probing the shift in the position of vibrational bands on isotopic substitution using infrared spectroscopy. Extensive ab initio calculations indicate that HArF is intrinsically stable, owing to significant ionic and covalent contributions to its bonding, thus confirming computational predictions11,12,13 that argon should form a stable hydride species with properties similar to those of the analogous xenon and krypton compounds reported before14,15,16,17,18.

New Statistical Models for Kinetic Theory: Methods of Construction

Abstract: A statistical model of the collision term in the Boltzmann equation is introduced which is similar in concept to the well‐known Krook model but yields the correct Prandtl number of ⅔ for a monatomic gas. A new method for constructing kinetic models is presented which is based on the information theory concept of entropy or uncertainty. This method, which is applicable to quite general systems in nonequilibrium statistical mechanics, is used to construct statistical models for multicomponent gas mixtures and for gases consisting of molecules with internal degrees of freedom.