Noble Gases Kr Research Articles

Anisotropies in electronic densities and electrostatic potentials of Halonium Ions: focus on Chlorine, Bromine and Iodine.

Why are the halonium cations so effective in forming strongly-bound complexes? We directed our research to address this question and we present electrostatic potential data for the valence-state halogen atoms X and halonium cations X+, where X = Cl, Br, I. The electron densities and electrostatic potentials of the halonium cations show considerably greater anisotropy than do the valence state halogens. The distances from the electrostatic potential surface maxima to the halogen nuclei are about 0.5Åsmaller than the distances from the electrostatic potential surface minima to the nuclei, giving the halonium cations each a more disk-like shape than the corresponding neutral valence state halogens. Their surface electrostatic potentials are totally consistent with the directionalities of halonium cations in complexes and the strengths of theirinteractions. To add perspective to this brief report, we have included calculations of the isotropic cation K+ and noble gas Kr. The calculations of the electrostatic potentials of the valence states of the halogen atoms Cl, Br and I and the halonium cations Cl+, Br+ and I+, as well as K+ and Kr, on 0.001 au contours of their electronic densities were carried out with Gaussian O9 and the Wave Function Analysis - Surface Analysis Suite (WFA-SAS) at the M06-2X/6-31 + G(d,p) and M06-2X/3-21G* levels.

Comparative Study of Pd/B4C X-ray Multilayer Mirrors Fabricated by Magnetron Sputtering with Kr and Ar Gas.

Ultrathin Pd/B4C multilayers are suitable X-ray mirrors working at the photon energy region of 7–20 keV. To further improve the layer structure, Pd/B4C multilayers with a d-spacing of 2.5 nm were fabricated by magnetron sputtering using the heavy noble gas Kr and compared with the conventional ones fabricated by Ar. Although the Kr-sputtering process can work at a lower pressure, the interface width—especially the interface roughness—is a little larger than that made by Ar. A stronger polycrystallization and a lower content of sputter gas atoms were found in the Kr-made sample, which can be explained by the joint effect from less recoiled particles and lower sputtering pressure. A good reflectance of 68% of the Kr made multilayer was measured at 10 keV, which is only slightly lower than that of the Ar made sample (71%).

Origin and significance of cosmogenic signatures in vesicles of lunar basalt 15016.

Lunar basalt 15016 (~3.3 Ga) is among the most vesicular (50% by volume) basalts recovered by the Apollo missions. We investigated the possible occurrence of indigenous lunar nitrogen and noble gases trapped in vesicles within basalt 15016, by crushing several cm‐sized chips. Matrix/mineral gases were also extracted from crush residues by fusion with a CO 2 laser. No magmatic/primordial component could be identified; all isotope compositions, including those of vesicles, pointed to a cosmogenic origin. We found that vesicles contained ~0.2%, ~0.02%, ~0.002%, and ~0.02% of the total amount of cosmogenic 21Ne, 38Ar, 83Kr, and 126Xe, respectively, produced over the basalt's 300 Myr of exposure. Diffusion/recoil of cosmogenic isotopes from the basaltic matrix/minerals to intergrain joints and vesicles is discussed. The enhanced proportion of cosmogenic Xe isotopes relative to Kr detected in vesicles could be the result of kinetic fractionation, through which preferential retention of Xe isotopes over Kr within vesicles might have occurred during diffusion from the vesicle volume to the outer space through microleaks. This study suggests that cosmogenic loss, known to be significant for 3He and 21Ne, and to a lesser extent for 36Ar (Signer et al. 1977), also occurs to a negligible extent for the heaviest noble gases Kr and Xe.

Ns2np4 (n = 4, 5) lone pair triplets whirling in M*F2E3 (M* = Kr, Xe): Stereochemistry and ab initio analyses

The stereochemistry of ns2np4 (n = 4, 5) lone pair LP characterizing noble gas Kr and Xe (labeled M*) in M*F2 difluorides is examined within coherent crystal chemistry and ab initio visualizations. M*2+ in such oxidation state brings three lone pairs (E) and difluorides are formulated M*F2E3. The analyses use electron localization function (ELF) obtained within density functional theory calculations showing the development of the LP triplets whirling {E3} quantified in the relevant chemical systems. Detailed ELF data analyses allowed showing that in α KrF2E3 and isostructural XeF2E3 difluorides the three E electronic clouds merge or hybridize into a torus and adopt a perfect gyration circle with an elliptical section, while in β KrF2 the network architecture deforms the whole torus into an ellipsoid shape. Original precise metrics are provided for the torus in the different compounds under study. In KrF2 the geometric changes upon β → α phase transition is schematized and mechanisms for the transformation with temperature or pressure are proposed. The results are further highlighted by electronic band structure calculations which show similar features of equal band gaps of 3 eV in both α and β KrF2 and a reorganization of frontier orbitals due to the different orientations of the F-Kr-F linear molecule in the two tetragonal structures.

Understanding the adsorption mechanism of noble gases Kr and Xe in CPO-27-Ni, CPO-27-Mg, and ZIF-8.

An experimental study of Xe and Kr adsorption in metal-organic frameworks CPO-27-Ni, CPO-27-Mg, and ZIF-8 was carried out. In situ synchrotron X-ray powder diffraction experiments allowed precise determination of the adsorption sites and sequence of their filling with increasing of gas pressure at different temperatures. Structural investigations were used for interpretation of gas adsorption measurements.

Amorphous In–Ga–Zn–O thin‐film transistors prepared by magnetron sputtering using Kr and Xe instead of Ar

AbstractHeavier noble gases Kr and Xe instead of the lighter Ar during the magnetron‐sputtering deposition of amorphous indium–gallium–zinc oxide films are introduced in fabricating their thin‐film transistors (TFTs). Heavy noble gases can reduce damage to film induced by ion bombardment during the sputtering depositions. Higher field‐effect mobility with better gate bias stability can be obtained in the heavier‐noble‐gas sputtered TFTs. Raman spectroscopic analysis and X‐ray reflectometry respectively suggest that the disordered structure in the film is suppressed, and the film becomes denser by introducing heavy noble gases, corresponding to the improvement of TFT performance.

Heavy noble gas (Kr, Xe) irradiated (111) InP nanoporous honeycomb membranes with enhanced ultrafast all-optical terahertz emission

Nanoporous honeycomb membranes on InP (111) surfaces emit ultrafast coherent terahertz pulses under near-infrared optical excitation. Irradiating the membranes with heavy noble gas Kr or Xe ions enhances the terahertz emission. The emission does not vary with in-plane magnetic field rotation and exhibits three-cycle dependence on azimuthal-angle rotation. Both suggest the terahertz source is not transient currents but optical rectification enhanced by the heavy-ion irradiation.

Synthesis of mesoporous amorphous silica by Kr and Xe ion implantation: Transmission electron microscopy study of induced nanostructures

Thermally grown amorphous SiO 2 was implanted at room temperature with heavy noble gases Kr and Xe in order to create cavities in the oxide and increase its porosity. The implantation energies were chosen in order to have the same implantation depth for both ions. Although both ions induce bubbles in amorphous SiO 2, bubble size and spatial distribution depend upon the ion mass. Moreover, Xe implantation leads to the additional formation of “nanoclusters”. Thermal stability of bubbles/cavities depends on the implanted ion. The nucleation of bubbles and nanoclusters in amorphous SiO 2 is discussed in terms of ion mobility, gas–defect interactions, and chemical interaction. Bubble growth is shown to occur by a migration and coalescence process.

Noble gas enrichments in porewater of estuarine sediments and their effect on the estimation of net denitrification rates

Abstract The concentration and the isotopic ratios of noble gases He, Ne, Ar, Kr and Xe were measured in porewater trapped in shallow sediments of the estuary of the St-Lawrence River, Quebec, Canada. The gases are atmospheric in origin but most samples have gas concentrations 1.7–28 times higher than those expected in solution in water at equilibrium with the atmosphere. Elemental fractionation of heavier noble gases Kr and Xe compared to Ar strongly suggests that noble gases were adsorbed on sediments or organic matter and then desorbed into porewaters due to depressurization, as collected samples were brought to the surface. Atmospheric Ar in porewater is used as a reference to measure the N2-fluxes at the water–sediment interface. Ignoring the Ar enrichments observed in porewater could lead to a severe underestimation of the denitrification rate in oceans and estuaries.

Neutron-Capture Elements in Planetary Nebulae: Identification of Two Near-Infrared Emission Lines as [K[CLC]r[/CLC] [CSC]iii[/CSC]] and [S[CLC]e[/CLC] [CSC]iv[/CSC

I propose that two previously unidentified lines at 2.199 and 2.287 μm seen in the spectra of planetary nebulae (PNs) are fine-structure transitions of Kr+2 and Se+3. These are the cosmically most abundant elements with Z > 32. The ionic stages and originating energy levels of the observed transitions are expected to be significantly populated under nebular conditions, and these elements—especially the noble gas Kr—are unlikely to be strongly depleted out of the gas phase into grains. Furthermore, their concentrations can be enhanced by s-processing, which occurs in the interiors of the PN progenitor stars. The observed line strengths are consistent with modest (factor of a few) overabundances. In support of the identification of the 2.199 μm line as [Kr III] 3P1-3P2, PNs that display this line also show [Kr III] 1D2-3P2 6828 A emission. I identify the 2.287 μm line as [Se IV] 2P3/2-2P1/2. These identifications suggest a new range of possibilities for line identifications in the infrared. In addition, the observability of emission lines from n-capture species introduces a novel approach for studying advanced evolutionary stages and nucleosynthesis in the progenitor stars and for more fully delineating the role of PNs as agents of galactic chemical enrichment.

CI calculations of the inner and outer valence photoelectron spectra of the fourth row hydrides

2h-1p CI and 3h-2v-1p CI calculations with relaxed orbitals are performed to investigate the outer and inner valence photoelectron spectra of the fourth row hydrides HBr, H 2Se, AsH 3 and GeH 4. The adequacy of the 2h-1p CI scheme is first analysed for the isoelectronic noble gas Kr. The experimental results available only for Kr and HBr are well reproduced by the calculations. For HBr confident assignment of the low energy shake-up structure is proposed. The strong similarity to the analogous third row compounds also gives confidence in the accuracy of the calculated spectra for the other hydrides and in the validity of the schemes employed to interpret the inner valence photoelectron spectra of such systems.

Noble gases and K-Ar ages in Aouelloul, Zhamanshin, and Libyan Desert impact glasses

Elemental abundances of noble gases and isotopic compositions of Ne and Ar have been determined in seven Aouelloul impact glasses, four Zhamanshin impact glasses, and one Libyan Desert glass sample. Similar to most other natural terrestrial glasses, a high Ne Ar ratio was observed in all impact glasses. The Ne concentrations in the impact glasses are of the same order of magnitude as those in tektites, but the concentrations of Ar (and the heavy noble gases Kr and Xe) are significantly higher than those in the tektites. As a result, the Ne Ar ratios in the impact glasses are lower than in tektites. The isotopic composition of Ne in the impact glasses is identical to that of air, as also observed in tektites, suggesting that the Ne is atmospheric in origin. From the K content of the glasses, we calculated K-Ar ages of 10–15 Ma for Aouelloul and 0.7–1.0 Ma for Zhamanshin impact glasses. For Zhamanshin glasses, these ages are in good agreement with other radiogenic and fission track ages, while for Aouelloul, our K-Ar ages agree with older K-Ar ages reported before, but not with the younger (~3.2 Ma) fission track ages.

Chernobyl radioactivity in size-fractionated aerosol

The Chernobyl accident released in the time from April 26th to May 6th 1986 roughly 1.9.10 Is Bq (without noble gases) of radioactive material into the atmosphere, which was spread over a large area of the northern hemisphere. This radioactivity was transported either as gaseous species (e.g. the noble gases Kr and Xe and the halogens I and Br) or adsorbed on aerosols. In addition, so-called hot particles have been observed. In order to understand and describe the general interaction of these airborne fission nuclides with the environment, it is essential to know the corresponding carriers, because they govern their long-range transport in the atmosphere. We have therefore measured activity distributions on size fractionated aerosol samples for typical fission products released during I~1 103 132 137 the Chernobyl accident such as I, Ru, Te and Cs. In the same samples we have also measured the concentrations of non-radioactive air pollutants such as sulfate and nitrate, in order to compare their distribution patterns.

On the Removal of Volatile Fission Products from Uranium-Bismuth Reactor Fuels

In the Liquid Metal Fuel Reactor (LMFR) the fuel is a dilute solution of U, Mg, and Zr in bismuth. At the operating fuel temperatures (400 to 550 deg C), the volatile fission products (FPV's), which represent about 25% of the total by weight, are mostly the noble gases Kr and Xe with small amounts of the halogen fission products Br and I. Owing to the facts that the LMFR is a thermal breeder reactor and that the 9.13-hr Xe/sup 135/) isotope has a 2.7 x 10/sup 6/-barn thermal cross section, the concentration of FPV's in the fuel and in the core must be kept very low for good neutron economy. For a 1% reactor poisoning level, and assuming no Xe adsorbed on or absorbed in the graphite, the concentrations of 9.13-hr Xe/sup 135) and total Xe in the fuel are estimated to be about 1.5 and 13 parts per billion, respectively, for a typical commercial plant. Complete isotopic compositions of the volatile fission products and poison levels for different removal rates are presented. The effect of various degrees of volatilization of the iodine and bromine on these factors are also shown. Xe represents over 80% by weight of themore » FPV's. Both Xe and its precursor, iodine, have strong tendencies to adsorb on unwetted surfaces and to penetrate graphite, the moderator material in the reactor core. Immobilization of Xe in the core would present a problem from the standpoint of reactor poisoning. Experimental results are presented to show the extents to which both iodine and Xe adsorb on steel and graphite and penetrate graphite. It appears that the Xe problem is not so much one of removing it from the fuel in a desorber as it is in preventing it from collecting on graphite surfaces in the core. (auth)« less