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J Zähringer - One of the best experts on this subject based on the ideXlab platform.
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Rare Gases in stony meteorites
Geochimica et Cosmochimica Acta, 2005Co-Authors: J ZähringerAbstract:Abstract The contents and isotopic composition of He, Ne and Ar in 81 stony meteorites have been determined. The 3He exposure ages, and the radiogenic 4He and K-Ar ages confirm the conclusions of previous publications. The exposure ages of diogenites are clustered around 20 × 106 yr. The H-chondrites Benoni, Cee Vee, Grassland, Heredia, Hessle and Menow, the L-chondrite Bishunpur and the carbonaceous chondrites Alais and Essebi contain He and Ne as primordial components. A dark inclusion in the amphoterite Krahenberg has an extremely high K-content of 12000 ppm. The contents of 84Kr and 132Xe and the 129Xe:132Xe ratio have also been determined in 92 stony meteorites. Not only the 84Kr and 132Xe contents but also the content of the 129Xe-excess are proportional to the primordial 36Ar content over a larger range. The primordial 36Ar contents are related to the petrological classes of Van Schmus and Wood . The 129Xe:132Xe ratios of all ordinary chondrites lie between 1 and 3 and all enstatite chondrites have ratios between 3 and 7. If one assumes the I-129Xe relation from the work by Reynolds and co-workers to be valid, one has to conclude that all ordinary chondrites had initially about the same Xe:I ratio and that most of them lost a large fraction of their primordial Rare Gases after the 129I decay while the high temperature fraction retained all of the 129Xe. This imposes quite narrow constraints on the model on I-129Xe dating.
P Cassen - One of the best experts on this subject based on the ideXlab platform.
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deep earth Rare Gases initial inventories capture from the solar nebula and losses during moon formation
Earth and Planetary Science Letters, 2001Co-Authors: D Porcelli, D Woolum, P CassenAbstract:The implications of mantle Rare gas characteristics for both the acquisition of Rare Gases from the solar nebula and subsequent losses to space are examined. There is at least one deep mantle reservoir rich in 3He and Ne that was trapped early in Earth history, with minimum concentrations obtained by closed system calculations. Ne isotopes indicate the presence of a component that has a solar composition. Xe isotopes indicate that extensive late losses occurred from the mantle as well as from the atmosphere. Calculations based on a simple two-stage evolution provide times of losses of up to ∼100 Ma after the formation of the solar system from both the mantle and the atmosphere. These losses appear to have depleted the Rare Gases by ≥97%; therefore, there originally was at least two orders of magnitude more Rare Gases than now present. Mechanisms for the capture of Rare Gases soon after the start of the solar system into the deep Earth (or Earth-forming materials) must provide these high initial concentrations, presumably in the high-energy environment of planetary accretion where strong degassing of solids might be expected to have occurred. A mechanism that satisfies these requirements is the dissolution in a magma ocean of Rare Gases from a dense primary atmosphere. A massive atmosphere of solar composition would have been captured if the Earth had formed prior to dispersal of the solar nebula. The underlying mantle would have melted due to the energy of accretion and the blanketing effect of this atmosphere. Rare Gases would then have entered the molten Earth by dissolution at the surface and downward advection. For typical solubility coefficients, a total pressure of ∼100 atm and surface temperatures of >∼2500°C are required to dissolve sufficient Rare Gases to account for the initial lower mantle concentrations. While Xe in the mantle is isotopically exchanging with the primary atmosphere, it will be buffered to a solar composition; therefore, somewhat less Xe must be trapped prior to the late loss event for longer periods of exchange. As solidification of the mantle proceeded outward during cooling, the distributions of retained Rare Gases would have been determined by the history of surface pressure and temperature during the coupled cooling of the Earth and atmosphere. The giant impact proposed for Moon formation may have been responsible for the inferred substantial and late gas losses from the deep mantle as well as from the atmosphere. Constraints on the timing of Moon formation derived from Hf–W systematics and simulations of the giant impact are consistent with the Xe isotope constraints for gas loss.
S Bratos - One of the best experts on this subject based on the ideXlab platform.
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a computer simulation study of hydrophobic hydration of Rare Gases and of methane i thermodynamic and structural properties
Journal of Chemical Physics, 1991Co-Authors: Bertrand Guillot, Y Guissani, S BratosAbstract:A theory is proposed to study the hydrophobic hydration of Rare Gases and methane in water. The Ostwald absorption coefficient γ, the hydration energy ΔE, and entropy ΔS are calculated by combining large‐scale molecular‐dynamics simulations and test‐particle methods. The convergence of calculations is checked with particular care. The structure of the first two hydration shells is analyzed in terms of appropriate pair distribution functions. The picture conveyed by this theory is compared to that provided by the early work.
J.g. Mccaffrey - One of the best experts on this subject based on the ideXlab platform.
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The absorption and excitation spectroscopy of matrix-isolated atomic manganese: Sites of isolation in the solid Rare Gases
Journal of Chemical Physics, 2005Co-Authors: M. Collier, J.g. MccaffreyAbstract:This study collects information from absorption and luminescence excitation spectra recorded for Mn atoms isolated in the solid Rare Gases Ar, Kr, and Xe and presents an analysis of the site occupancy, based on the polarizabilities of the Rare Gases and the observed spectral shifts. Two thermally stable sites of isolation exist for atomic Mn in solid Ar and Kr, while a single thermally stable site is present in Mn/Xe. Site occupancy assignments are based on the application of a polarizability model to the z P-6(5/2)
Vincent M Donnelly - One of the best experts on this subject based on the ideXlab platform.
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trace Rare Gases optical emission spectroscopy nonintrusive method for measuring electron temperatures in low pressure low temperature plasmas
Physical Review E, 1999Co-Authors: M V Malyshev, Vincent M DonnellyAbstract:Trace Rare Gases optical emission spectroscopy (TRG-OES) is a new, nonintrusive method for determining electron temperatures ${(T}_{e})$ and, under some conditions, estimating electron densities ${(n}_{e})$ in low-temperature, low-pressure plasmas. The method is based on a comparison of atomic emission intensities from trace amounts of Rare Gases (an equimixture of He, Ne, Ar, Kr, and Xe) added to the plasma, with intensities calculated from a model. For Maxwellian electron energy distribution functions (EEDFs), ${T}_{e}$ is determined from the best fit of theory to the experimental measurements. For non-Maxwellian EEDFs, ${T}_{e}$ derived from the best fit describes the high-energy tail of the EEDF. This method was reported previously, and was further developed and successfully applied to several laboratory and commercial plasma reactors. It has also been used in investigations of correlations between high-${T}_{e}$ and plasma-induced damage to thin gate oxide layers. In this paper, we provide a refined mechanism for the method and include a detailed description of the generation of emission from the Paschen $2p$ manifold of Rare Gases both from the ground state and through metastable states, a theoretical model to calculate the number density of metastables ${(n}_{m})$ of the Rare Gases, a practical procedure to compute ${T}_{e}$ from the ratios of experimental-to-theoretical intensity ratios, a way to determine the electron density ${(n}_{e}),$ a discussion of the range of sensitivity of TRG-OES to the EEDF, and an estimate of the accuracy of ${T}_{e}.$ The values of ${T}_{e}$ obtained by TRG-OES in a transformer-coupled plasma reactor are compared with those obtained with a Langmuir probe for a wide range of pressures and powers. The differences in ${T}_{e}$ from the two methods are explained in terms of the EEDF dependence on pressure.
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ultrahigh frequency versus inductively coupled chlorine plasmas comparisons of cl and cl2 concentrations and electron temperatures measured by trace Rare Gases optical emission spectroscopy
Journal of Applied Physics, 1998Co-Authors: M V Malyshev, Vincent M Donnelly, Seiji SamukawaAbstract:Using trace Rare Gases optical emission spectroscopy, Cl and Cl2 number densities (nCl and nCl2) and electron temperatures (Te) were measured for two source configurations of high-density chlorine plasmas. In one configuration, the reactor was outfitted with a spoke antenna, operated at a resonant ultrahigh frequency (UHF) of 500 MHz. Alternatively, the same reactor was configured with a single loop, inductively coupled plasma (ICP) source operated at a radio frequency of 13.56 MHz. Optical emission from trace amounts (1% each) of Rare Gases added to the main Cl2 feed gas were recorded as a function of power and pressure. Modeling was used to derive Te from these data. Additional emission from Cl2 (at 3050 A) and Cl (numerous lines between 7000 and 9000 A), normalized to the appropriate emission from the Rare Gases (i.e., actinometry) was used to obtain nCl2 and nCl. In the ICP plasma, Te decreased monotonically from 5.5 to 1.2 eV as a function of increasing pressure between 1 and 20 mTorr. Conversely, wi...
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trace Rare Gases optical emission spectroscopy for determination of electron temperatures and species concentrations in chlorine containing plasmas
Japanese Journal of Applied Physics, 1998Co-Authors: Vincent M Donnelly, M V Malyshev, Avi Kornblit, Nicolas A Ciampa, J I Colonell, John T C LeeAbstract:Trace Rare gas optical emission spectroscopy has been used to obtain electron temperatures (Te) and percent dissociation of Cl2 in chlorine-containing, high-density inductively (transformer) coupled plasmas. In this method, a small amount of an equal mixture of the Rare Gases is added to the plasma and emission spectra that include lines from the Rare Gases are recorded. Modeling of the dependence of the Rare gas emission intensities on Te allows Te to be derived from the best match between the observed and computed intensities. Te in Cl2 plasmas increases from 1.7 eV at 20 mTorr to 3.4 eV at 0.5 mTorr. These values are 1.3 to 1.8 times lower than those recorded with a Langmuir probe. This discrepancy is due at least in part to artifacts associated with using a single Langmuir probe in a reactor with semiinsulating walls. Absolute percent dissociations of Cl2 were determined by monitoring the intensity of an emission band of Cl2, normalized to emission from Ar and Xe. Cl2 percent dissociation increased with power and decreased with pressure. At 1.0 mTorr, Cl2 is about 85% dissociated at a power density of 0.1 W/cm3 and 95% dissociated at 0.3 W/cm3 in a Cl2 plasma. Addition of BCl3 to Cl2 increases the dissociation of Cl2.