Comparison of temperature measurements in ICP and MIP with Ar and He as plasma gas

Various temperature measurements have been carried out in microwave induced plasmas (MIP) generated with a surfatron and inductivcly coupled plasmas (ICP) both with argon and helium as plasma gas. Iron has been used for the determination of excitation temperature, and OH and N⁺₂ for rotational temperatures. In the case of the Ar ICP, equilibrium is attained between the various temperatures (4500 K), as previously described. On the other hand, in the He ICP and the MIPs, iron provides the highest temperature (4500 K) but discrepancies are obtained with results from N⁺₂ and OH. These two species show lower values, especially OH (2000 K).     

Coordination of niobium and tantalum oxides by Ar, Xe and O2: Matrix isolation infrared spectroscopic and theoretical study of NbO2(Ng)2 (Ng = Ar, Xe) and MO4(X) (M = Nb, Ta; X = Ar, Xe, O2) in solid argon

The combination of matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that the NbO₂ molecule is coordinated by two noble gas atoms in forming the NbO₂(Ng)₂ (Ng = Ar, Xe) complexes in solid noble gas matrixes. In contrast, the TaO₂ molecule is not able to form similar noble gas complex. The niobium and tantalum dioxides further react with dioxygen to form the side-on bonded superoxo-dioxide complexes MO₄ (M = Nb, Ta), which are coordinated by one argon atom in solid argon matrix. The coordinated Ar atom in MO₄(Ar) can be replaced by O₂ or Xe in forming the MO₆ and MO₄(Xe) complexes. The results indicate that the NbO₂, NbO₄ and TaO₄ molecules trapped in solid noble gas matrixes should be regarded as the NbO₂(Ng)₂ and MO₄(Ng) (Ng = Ar, Xe; M = Nb, Ta) complexes instead of “isolated” metal oxide species.     

Solubility of non polar gases in formaldehyde diethyl acetal between-10 and 30°C,and 1 Atm partial pressure of gas

Solubility measurements of the gases He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂ in formaldehyde diethyl acetal in the range of –10 to 30°C, and a gas partial pressure of 1 atmosphere (101.32 kPa) are reported. Standard changes of thermodynamic functions for the solution process are evaluated. The scaled particle theory is used to obtain the effective Lennard-Jones 6, 12 pair potential parameters for formaldehyde diethyl acetal. Experimental solubilities values are compared with those obtained from the application of the scaled particle theory to gas liquid solubility.     

Solubility of nonpolar gases in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2,2,2-trifluoroethanol at 25°C and 101.33 kPa partial pressure of gas are reported. Gibbs energy for the solution process at 25°C is evaluated from the experimental values of the solubility of gases expressed as mole fraction. Lennard-Jones 6–12 pair potential parameters for 2,2,2-trifluoroethanol are estimated by using the scaled particle theory (SPT); and experimental solubilities are compared with those calculated from the values of these parameters through the SPT model.     

Noble‐Gas Complexes: Theoretical Investigation of Multicenter Polynuclear Species

Ab initio calculations at the MP2 level of theory disclose the conceivable existence of neutral complexes containing four or five distinct noble gases (Ng) each bound to a distinct Be‐atom. These multicenter polynuclear Ng molecules are formally obtained by replacing the H‐atoms of CH₄ and but‐2‐yne with ? NBeNg moieties, which behave as independent monovalent ‘functional groups’. Our investigated complexes include the five homotetranuclear [C(NBeNg)₄] complexes 1 – 5 (Ng=He? Xe), the five heterotetranuclear complexes [CN₄Be₄(He)(Ne)(Ar)(Kr)] ( 6 ), [CN₄Be₄(He)(Ne)(Ar)(Xe)] ( 7 ), [CN₄Be₄(He)(Ne)(Kr)(Xe)] ( 8 ), [CN₄Be₄(He)(Ar)(Kr)(Xe)] ( 9 ), and [CN₄Be₄(Ne)(Ar)(Kr)(Xe)] ( 10 ), and the heteropentanuclear complex [HC₄N₅Be₅(He)(Ne)(Ar)(Kr)(Xe)] ( 11 ). We also investigated the five model complexes [H₃CNBeNg] (Ng=He? Xe) containing a single ? NBeNg moiety. The geometries and vibrational frequencies of all these species, invariably characterized as minimum‐energy structures, were computed at the MP2(full)/6‐31G(d,p)/SDD level of theory, and their stability with respect to the loss of the various Ng‐atoms was evaluated by single‐point calculations at the MP2(full)/6‐311G(d)/SDD level of theory. The beryllium‐Ng binding energies range from ca. 17 (Ng=He) to ca. 63 (Ng=Xe) kJ/mol, and the results of natural‐bond‐orbital (NBO) and atoms‐in‐molecules (AIM) analysis reveal that the Be? Ng interaction is essentially electrostatic for helium, neon, argon, and krypton, and has probably a small covalent contribution for xenon.     

Angle and bond-length dependent C6 coefficients for H2 interacting with H,Li, Be and rare gas atoms

Summary Accurate new C₆ dispersion energy coefficients, and their dependence on the diatom orientation and bond length, are calculated for molecular hydrogen interacting with an atom of H, Li, Be, He, Ne, Ar, Kr or Xe. They are generated from accurateab initio pseudo dipole oscillator strength distributions (DOSD) for H₂, H, He and Be, and reliable semiempirical ones for Li, Ne, Ar, Kr and Xe. Compact power series expansions for the diatom bond-length dependence of these coefficients, suitable for incorporation into representations of full potential energy surfaces for these systems, are determined and assessed.     

Effect of variation in argon content of calibration gases on determination of atmospheric carbon dioxide

Carbon dioxide (CO₂) is a greenhouse gas that makes by far the largest contribution to the global warming of the Earth's atmosphere. For the measurements of atmospheric CO₂ a non-dispersive infrared analyzer (NDIR) and gas chromatography are conventionally being used. We explored whether and to what degree argon content can influence the determination of atmospheric CO₂ using the comparison of CO₂ concentrations between the sample gas mixtures with varying Ar amounts at 0 and 18.6 mmol mol⁻¹ and the calibration gas mixtures with Ar at 8.4, 9.1, and 9.3 mmol mol⁻¹. We newly discovered that variation of Ar content in calibration gas mixtures could undermine accuracy for precise and accurate determination of atmospheric CO₂ in background air. The differences in CO₂ concentration due to the variation of Ar content in the calibration gas mixtures were negligible (<±0.03 μmol mol⁻¹) for NDIR systems whereas they noticeably increased (<±1.09 μmol mol⁻¹) especially for the modified GC systems to enhance instrumental sensitivity. We found that the thermal mass flow controller is the main source of the differences although such differences appeared only in the presence of a flow restrictor in GC systems. For reliable monitoring of real atmospheric CO₂ samples, one should use calibration gas mixtures that contain Ar content close to the level (9.332 mmol mol⁻¹) in the ambient air as possible. Practical guidelines were highlighted relating to selection of appropriate analytical approaches for the accurate and precise measurements of atmospheric CO₂. In addition, theoretical implications from the findings were addressed.     

Dynamic separation of Xe and Kr by metal-organic framework and covalent-organic materials: a comparison with activated charcoal

We systematically investigate dynamic separation of Xe and Kr at room temperature using four representative porous materials (Cu-BTC, ZIF-8, COP-4 and activated carbon (AC)). Results indicate that among the four materials, Cu-BTC not only shows the highest retention volume per gram (V_g=788 mL g^-1, which is 1.8 times of activated carbon (436 mL g^-1)) under flowing condition, but also can separate 350 ppm Xe from 35 ppm Kr mixture in air with a high Xe/Kr selectivity of 8.6 at room temperature and 200 kPa, due to its suitable pore morphology, open metal sites, small side pockets in the framework. Moreover, the Cu-BTC also performs well on individual separation of Xe, Kr, CO₂ from five-component gas mixture (Xe:Kr:CO₂:Ar:N₂=1:1:1:1:0.5, V/V) and has the longest retention time for Xe (20 min) in gas chromatographic separation, suggesting that it is a good candidate for potential applications as polymeric sieves.     

Dielectric breakdown characteristics of a high current metal vapor plasma

Time- and spatially-resolved spectroscopy is used to study the early-time spectral features of the plasmas produced by high-current, capacitive discharges through thin silver films. Spectra are compared for several support gases including CO₂, He, and an Ar/O₂ mixture. All measurements were made during the first 40 μs of the discharge. At atmospheric pressure for all three gases, spectra from support gas species show intense lines for only a brief interval between 10 and 30 μs after the start of the discharge. Greatest intensity from silver lines always occurs at the film surface; while greatest intensity from support gas species occurs about 2.0 mm from the film surface. A magnetic field of a few kG normal to the electric field in the plasma and parallel to the thin film surface almost completely eliminates spectral lines from the support gas species.     

Structural contribution to the effect of hydrophobic hydration of noble gases

Within the concepts of structurally-thermodynamic characteristics of solvation and pseudo-chemical potential, the sample collection of the most authentic experimental data on solubility of gaseous He, Ne, Ar, Kr, Xe, and Rn in H₂O and D₂O is analysed at ≈0.1 MPa and T = 278–318 K. The conclusion is drawn that at deuteration of water molecules and also with increasing molar mass of noble gas, the relative contribution of effect of its hydrophobic hydration decreases. However in case of pass from lightweight noble gases (He, Ne, Ar) to heavy ones (Kr, Xe, Rn), structural transformations in their aqueous solutions become more expressed as a whole due to strengthening interaction between dissolved substance and solvent.     

Photolytic cage effect of iodine in gases at high pressures

The photolysis of iodine has been studied in the gas phase using laser flash photolysis at 6943 A. The dependence of the quantum yield on the pressure has been investigated in the range 0.1–1000 atm for several inert gases. For Kr, Xe, O₂, CO₂, CH₄, C₂H₆ and C₃H₈ a decrease of the quantum yield with increasing pressure was obtained; for He, Ne, Ar and H₂ no effect could be observed. These results may correspond to a photolycitc cage effect of iodine in the gas phase analogous to that known from the liquid phase.     

Solubility of gases in butanols: IV. Solubilities of nonpolar gases in 2-methyl-2-propanol at 303.15 K and 101.33 kPa partial pressure of gas

Solubilities of 15 nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, O₂, CH₄, C₂H₄, C₂H₆, CF₄, SF₆, and CO₂) in 2-methyl-2-propanol (tert-butanol) have been measured at the temperature 303.15 K and 101.33 kPa partial pressure of gas. Standard changes of the Gibbs energy of solution have been also determined from experimental data. The Lennard–Jones 6,12 pair potential parameters have been estimated for that solvent using the Scaled Particle Theory (SPT) and these parameters have been compared with those corresponding to the other isomers of butanol. It can be concluded that the derived energy parameters provide a measurement of the association of the alkanol. A version of the UNIFAC model has been applied and the corresponding interaction parameters for alkanes and alkanols have been determined.     

A molecular dynamics simulation of rebound,capture and diffusion in collisions at thermal energies between a rare gas atom and an argon cluster (n=125)

Molecular dynamics calculations have been performed to simulate the low energy collision (0.2 eV) of a rare gas atom (He, Ar, Xe) with a cluster of 125 argon atoms. Depending on its relative mass to argon, the projectile is either deflected (He) or captured (Ar, Xe) by the argon cluster. We have determined the deflection function of the He projectile that is scattered, and for Xe we have determined wether it stays near the surface of the cluster or migrates inside. These results have been discussed in the light of very simple models.     

Gas transport in polybutadiene treated with aqueous bromine

Diffusion, solubility, and permebility coefficients were measured for He, Co₂, Ar, and CH₄ in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X-ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO₂, Ar, and CH₄ decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO₂, Ar, and CH₄ became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley & Sons, Inc.     

Solubility of nonpolar gases in tetrahydrofuran at 0 to 30°C and 101.33 kPa partial pressure of gas

Solubility measurements of several nonpolar gases (He, Ne, Ar, Kr, Xe, H₂, D₂, N₂, CH₄, C₂H₄, C₂H₆, CF₄ and SF₆) in tetrahydrofuran from 0 to 30°C and 101.33 kPa partial pressure of gas are reported. Thermodynamic functions for the solution process (Gibbs energy, enthalpy, and entropies) at 25°C are evaluated from experimental values of gas solubility as mole fractions and their variation with temperature. Lennard-Jones 6–12 pair potential parameters for tetrahydrofuran are estimated using the scale particle theory; experimental solubilities as mole fraction are compared with values calculated using this theory.     

Classical rotational and centrifugal sudden approximations for atom—molecule collisional energy transfer

The application of centrifugal and rotational sudden approximations to classical trajectory studies of rotational energy transfer in atom—molecule collisions to examined. Two different types of approximations are considered: a centrifugal sudden (CS) approximation, in which the orbital angular momentum is assumed to be constant during collisions, and a classical infinite order sudden (CIOS) approximation, in which the CS treatment is combined with an energy sudden approximation to totally decouple translational and rotational equations of motion. The treatment of both atom plus linear and nonlinear molecule collisions is described, including the use of rotational action-angle variables for the rotor equations of motion. Applications of both CS and CIOS approaches to rotational energy transfer in He + I₂ collisions are presented. We find the calculated CS and CIOS rotationally inelastic cross sections are in generally good agreement [errors of (typically) 10–50%] with accurate quasiclassical (QC) ones, with the CS results slightly more accurate than CIOS. Both methods are less accurate for small |Δj| transitions than for large |Δj| transitions. Computational savings for the CS and CIOS applications is about a factor of 3 (per trajectory) compared to QC. We also present applications using the CS method to rotational energy transfer in He, Ar, Xe + O₃ collisions, making comparisons with analogous QC results of Stace and Murrell (SM). The agreement between exact and approximate results in these applications is generally excellent, both for the average energy transfer at fixed impact parameters, and for rotationally inelastic cross sections. Results are better for He + O₃ and Ar + O₃ than for Xe + O₃, and better at low temperatures than at high. Since SM's quasiclassical treatment considered only total internal energy transfer without attempting a partitioning between vibration and rotation, while our CS calculation considers only rotational energy transfer, the observed good agreement between our and SM's cross sections indicates that most internal energy transfer in He, Ar, Xe + O₃ is rotational. The relation of this result to models of the activation process in thermal unimolecular rate constant determination is discussed.     

Absolute CO2/Xenon Separation in Ultramicropore MOF for Anesthetic Gases Regeneration

Xe is an ideal anesthetic gas, but it has not been widely used in practice due to its high cost and low output. Closed-circuit Xe recovery and recycling is an economically viable method to ensure adequate supply in medical use. Herein, we design an innovative way to recover Xe by using a stable fluorinated metal-organic framework (MOF) NbOFFIVE-1-Ni to eliminate CO₂ from moist exhaled anesthetic gases. Unlike other Xe recovery MOFs with low Xe/CO₂ selectivity (less than 10), NbOFFIVE-1-Ni could achieve absolute molecular sieve separation of CO₂/Xe with excellent CO₂ selectivity (825). Mixed-gas breakthrough experiments assert the potential of NbOFFIVE-1-Ni as a molecular sieve adsorbent for the effective and energy-efficient removal of carbon dioxide with 99.16 % Xe recovery. Absolute CO₂/Xe separation in NbOFFIVE-1-Ni makes closed-circuit Xe recovery and recycling can be easily realized, demonstrating the potential of NbOFFIVE-1-Ni for important anesthetic gas regeneration under ambient conditions.     

Effect of internal excitation on the collision-induced dissociation and reactivity of Co 2 +

The kinetic energy dependence of collision-induced dissociation (CID) of dicobalt ion (Co ₂ ⁺ ) with He, Ar, and Xe has been investigated using guided ion-beam mass spectrometry. The change in efficiency of CID as the target gas is changed is in general agreement with previous CID studies of other systems: the cross section with Ar is 0.5 that with Xe, and no product ions are found with He. By varying the conditions under which the reactant ions are formed, the degree of internal excitation of the dicobalt ions is changed. The internal energies can be characterized by a Maxwell-Boltzmann distribution. We find that CID and reactions with O₂ and CO are very sensitive to Co ₂ ⁺ internal energy. The bond-dissociation energy derived from this work is D^o(Co ₂ ⁺ )=2.75±0.10 eV (63.4±2.3 kcal/mol). The Co ₂ ⁺ results are compared with a previous study of Fe ₂ ⁺ .     

Vacuum-ultraviolet photolysis of XeF2: XeF(B) fluorescence and quenching

Photolysis of XeF₂ with Kr(123.6 nm), Hg(184.9 nm) and CO(160 to 180 nm) resonance radiation gives strong XeF[B($\text{1}\text{2}$)?X²Σ⁺] fluorescence. The two shorter wavelengths also give weak XeF[D($\text{1}\text{2}$)?X²Σ⁺] emission. The XeF(B) vibrational distribution varies with photon energy and with pressure of added buffer gas. The addition of Xe and molecular gases results in quenching of the XeF^* emision. Stern-Volmer plots of the XeF^* emission intensity were used to obtain quenching rate constants for Xe, N₂, CO₂, NF₃ and F₂. The XeF(BX) emission intensity is diminished by ≈ 50% with addition of one atm of Ar.     

Gas permeability,diffusivity, and solubility of poly(4-vinylpyridine) film

Although poly(4-vinylpyridine) is believed to have good gas permselectivity, the intrinsic gas permeation property is rarely reported in the literature. The objective of this work is to study the the intrinsic gas permeation property of poly(4-vinylpyridine) using a free-standing film. Because of its brittleness and strong adhesion with most solid surfaces, a free-standing poly(4-vinylpyridine) film was therefore prepared from casting on a liquid mercury surface. The permeation behavior of He, H₂, O₂, N₂, CH₄, and CO₂ through the film was tested over a pressure range of 252 to 800 cm Hg at 35°C. The permeability and solubility decrease slightly with an increase in pressure, whereas the diffusivity increases as pressure increases. The pressure-dependent phenomenon can be explained using the partial immobilization model and the dual sorption model. An effective gas molecule diameter, which is defined as the square root of the product of gas collision and kinetic diameters, was used to correlate the diffusivity and gas molecule size, and an empirical equation was derived. Solubility is also a strong function of gas physical properties such as critical temperature and Lennard–Jones force constant, which are the measures of gas condensability and molecule interaction, respectively. In general, higher solubility in a polymer is obtained for gases with greater condensability and stronger interaction. Typical gas permeabilities of poly(4-vinylpyridine) measured at 619 cm Hg and 35°C are: 12.36 (He), 12.64 (H₂), 3.31 (CO₂), 0.84 (O₂), 0.14 (CH₄), and 0.13 (N₂) barrers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2851–2861, 1999