Noble Gases Ne Research Articles

The origin of air-like noble gases in MORB and OIB

Interpretation of the noble gas (Ne, Ar, Kr and Xe) isotopic composition of Ocean Island and Mid Ocean Ridge basalt (OIB and MORB) glass is complicated by the near surface addition of atmosphere-derived noble gases. Although the noble gas elemental composition in these samples is often similar to modern air, equilibration between a seawater vapor phase and a basalt melt can produce similar values in the melt phase [Patterson et al., Geophys. Res. Lett. 17 (1990) 705–708]. With the assumption that laboratory handling must reverse any surficial modern air contamination, it has often been concluded that the measured ‘air-like’ noble gases are introduced into MORB and OIB glass by variable interaction of the magma with seawater, either before or during eruption. Harrison et al.[Earth Planet. Sci. Lett. 171 (1999) 199–207] have recently demonstrated that both MORB popping rock and subglacially erupted Iceland OIB glass contain a component with 130Xe/ 22Ne indistinguishable from modern air. 84Kr/ 22Ne and 36Ar/ 22Ne are also indistinguishable from modern air for air values of 20Ne/ 22Ne. Assuming that the mode of this ‘air-like’ component addition is the same in both systems we show that calculated fractionation values for melt/seawater and melt/freshwater–glacier systems respectively cannot produce the observed elemental abundance pattern. We argue that the dominant source of ‘air-like’ noble gases in both the MORB and OIB is contamination by unfractionated modern air during sampling or sample preparation within the laboratory. We show that this is related to vesicularity and does not appear to be fully removed by current laboratory techniques. Because vesicularity is related to eruption depth and volatile content [J.G. Moore, Nature 282 (1979) 250–253], recently observed correlations between atmosphere-derived noble gases with radiogenic Pb, water content or other trace element pairs [Sarda et al., Science 283 (1999) 666–668; Bach and Niedermann, Earth Planet. Sci. Lett. 160 (1998) 297–309] may not reflect a relationship between these species in the magmatic source. Similarly, the conclusion from the existing MORB and OIB data set that the terrestrial mantle heavy noble gases have many similar features to modern air [Ozima and Igarashi, Earth Planet. Sci. Lett. 176 (2000) 219–232] is premature. These observations can be equally well accounted for by eruption style related vesicularity and related air contamination.

Noble gases in pyroxenites and metasomatised peridotites from the Newer Volcanics, southeastern Australia: implications for mantle metasomatism

The elemental and isotopic compositions of five noble gases (He, Ne, Ar, Kr and Xe) have been determined in selected, well-documented, ultramafic xenoliths from southeastern Australia. These xenoliths include both spinel-bearing peridotites with an apparent metasomatic overprint and garnet-bearing pyroxenites. In general, helium, neon, argon and xenon isotopic ratios from gases trapped in fluid inclusions of the samples are mid-ocean ridge basalt (MORB)-like, as has previously been found in anhydrous lherzolite xenoliths from the same area. In addition to the MORB-like components, radiogenic ( 4He*) and nucleogenic ( 21Ne* and 22Ne*) components were found in the present samples, reflecting relatively high U and Th contents in the metasomatic minerals such as amphibole, apatite and clinopyroxene. These components are only released upon melting, thus are likely to be trapped in the crystal lattices of the minerals. The MORB-like noble gas component found in fluid inclusions (invariably CO 2-rich) of these samples probably was introduced into the lithospheric mantle by metasomatising melts derived from the upper mantle. The noble gases dissolved in the metasomatising melt are likely to be effectively decoupled from incompatible elements during segregation of a CO 2-rich fluid in the ascending melt. In the metasomatising melt, the noble gases would partition into the CO 2-rich fluid whereas the incompatible elements would remain in the melt phase. As a result, the noble gas composition in fluid inclusions of the minerals appears to be independent of their degree of metasomatism indicated by their host rock mineralogy and trace elemental geochemistry. Once noble gases are trapped in CO 2-rich fluid inclusions within the minerals, they would preserve their source signatures without being affected significantly by the ingrowth of radiogenic and nucleogenic products, because the U, Th and K would remain in the melt. The predominance of MORB-like noble gas signatures in fluid inclusions of the xenoliths suggests that the metasomatising components were derived from the asthenospheric mantle underlying southeastern Australia.

Pressure dependence of Si/SiO2 degradation suppression by helium

The suppression of thermally induced generation of hole traps in SiO2 layers of Si/SiO2 and poly-Si/SiO2/Si structures by He ambient is analyzed as a function of the gas pressure p. The pressure dependence of the suppression efficiency is found close to p2/3. This pressure dependence and the observed reduced suppression efficiency of heavier noble gases (Ne, Ar) are interpreted as indications that the gas atom dissolved in SiO2 should approach close to the degradation-prone site in order to prevent the thermally induced bond break. This result suggests that a short-range interaction between noble gas atoms and the Si/SiO2 network atoms is at the basis of the degradation blockage effect.

Late-Quaternary Recharge Determined from Chloride in Shallow Groundwater in the Central Great Plains

An extensive suite of isotopic and geochemical tracers in groundwater has been used to provide hydrologic assessments of the hierarchy of flow systems in aquifers underlying the central Great Plains (southeastern Colorado and western Kansas) of the United States and to determine the late Pleistocene and Holocene paleotemperature and paleorecharge record. Hydrogeologic and geochemical tracer data permit classification of the samples into late Holocene, late Pleistocene–early Holocene, and much older Pleistocene groups. Paleorecharge rates calculated from the Cl concentration in the samples show that recharge rates were at least twice the late Holocene rate during late Pleistocene–early Holocene time, which is consistent with their relative depletion in 16O and D. Noble gas (Ne, Ar, Kr, Xe) temperature calculations confirm that these older samples represent a recharge environment approximately 5°C cooler than late Holocene values. These results are consistent with the global climate models that show a trend toward a warmer, more arid climate during the Holocene.

Quantum Number Dependence of Lineshift Coefficients Induced by Collisions with Noble Gas Perturbers in the ν3 Band of NO2

To complete our study concerning lineshift in the rovibrational spectrum of 14N16O2, a pulse-driven three-channel lead salt diode laser spectrometer was applied to record high-resolution spectra at room temperature in the 6.2-μm region corresponding to the ν3 band at low NO2 concentrations. The shift was studied for collisions with the noble gases He, Ne, Ar, Kr, and Xe. This paper extends our recently published data in order to analyze the quantum number dependence of the shift effect more precisely. Therefore, in this paper, additionally eight unresolved NO2 doublets covering an enlarged quantum number range (10 ≤ N″ ≤ 34, 2 ≤ K″a ≤ 6) were studied. For all doublets, shift coefficients δNO2–noble gas and additionally broadening coefficients γNO2–noble gas were determined. Hereby, the experimental data confirm general trends published recently. In this study, in the case of broadening for the lighter rare gases helium, neon, and argon, only a slight decrease of γNO2–noble gas was observed, whereas for the rare gases with a higher atomic weight, i.e., krypton and xenon, a pronounced decrease of γNO2–noble gas with increasing rotational quantum number N″ occurred. All measured lineshift coefficients were negative. The absolute value of the determined lineshift coefficient ‖δNO2–noble gas‖ increases with the mass of the noble gas perturber, i.e., ‖δNO2–He‖ < ‖δNO2–Ne‖ < ‖δNO2–Ar‖ < ‖δNO2–Kr‖ < ‖δNO2–Xe‖. Within the studied quantum number range, an increase ‖δNO2–noble gas‖ with increase of N″ was observed. A typical trend of the shift and broadening data on the quantum number K″a was not observed.

Noble gas induced line-shift and line-broadening in the ν2 band of H2S

The rotational dependence of pressure-induced shift and broadening of H2S absorption lines in the ν2 band due to collisions between H2S molecules and atoms of noble gases (He, Ne, Ar, Kr, and Xe) were studied in the spectral region between 1050 and 1325cm−1. The measurements were carried out using an improved pulse-driven diode laser spectrometer, allowing a new tuning technique of the diode laser. The parameters of this set-up will be compared to the parameters of the previously used spectrometer. The data concerning collisional broadening and shift coefficients, γ and δ, respectively, and their dependencies on the rotational quantum number, J″, mass, and the polarizability, α, of the noble gases are presented for 14 P-branch transitions (3≤J″≤8), seven Q-branch transitions (7≤J″≤10), and 18 R-branch transitions (2≤J″≤11). The broadening coefficients were determined with an accuracy of 1% (3.5×10−4cm−1/atm) and shift coefficients were determined with an uncertainty of less than 5×10−4cm−1/atm for the majority of lines and broadening gases. The qualitative explanation of experimental results was made based on the models and interactions also used in the ATC and CRB theories, respectively.

Photoacoustic measurements of the vibrational relaxation of the selectively excited ozone (ν3) molecule in pure ozone and its binary mixtures with O2, N2, and noble gases

The vibrational-translational relaxation time of the ν3 state of ozone was deduced from the phase shift of the photoacoustic detector signal relative to the amplitude-modulated radiation of the CO2 laser used for excitation of O3. A special photoacoustic cell with a third electrode is used to eliminate an instrumentation phase shift caused by inertia of the microphone membrane. A three-level kinetic model of O3 is presented and used to fit the experimental and calculated phase shifts to determine the vibrational relaxation rate coefficients for pure O3 and binary mixtures of O3 with O2, N2, and noble gases He, Ne, Ar, Kr, and Xe. These results are presented and compared with experimental data obtained for O3, O3–O2, and O3–N2 by fluorescence and double resonance techniques. Experimental data for ν3 state relaxation in binary mixtures with all noble atoms have been obtained for the first time. These new results are compared with the simplest model of interaction. Thus we obtain a very good agreement for the decrease of constants with the increase of the colliding partner mass.

Chemical (He, H2, CH4, Ne, Ar, N2) and isotopic (He, Ne, Ar, C) variations at the solfatara crater (southern italy): mixing of different sources in relation to seismic activity

Here we describe temporal variations of noble gas (He, Ne and Ar), carbon isotopes and chemical data of fluids collected at the Bocca Grande fumarole (Solfatara crater) from 1990 to 1994, before the occurrence of a seismic swarm. After more than seven years of quiescence, a sudden vertical ground deformation and a seismic swarm of 100 quakes with an Mmax = 1.5 with epicenter located beneath the Solfatara crater, was recorded from August 23 to 25 1994. Isotopic composition of He, Ne, Ar and C (from CO2) and abundances of He, Ne, Ar, H2, CH4 and N2 have been analysed from fumarolic fluids collected at the Solfatara crater. To date these isotopic ratios have not been used as precursors of earthquakes, although several cases have been reported in which the helium isotopic ratio was used to interpret volcanic unrest. All the analyzed isotopic ratios, chemical species and a calculated equilibrium temperature show a significant change a few months before the occurrence of the seismic activity and ground deformation, followed by a sudden return to values recorded prior the swarm. Migration towards the surface of deep (and hotter) gas phase related to crustal and magmatic sources with the following decrease of the surficial atmospheric component is the cause of such wide variations.

Neon excess in pumice: volcanological implications

We measured the noble gas abundance and Ne and Ar isotopic compositions in pumice samples from Japan and the Eolian Islands, Italy. The goal was to give clues on the mechanism of air incorporation into pumice and its relationship with eruption processes. The samples contain large excesses of atmospheric Ne over Ar, with 20 Ne/ 36 Ar ratios up to 600 times the atmospheric ratio. This excess is produced by the preferential diffusion of Ne over Ar in pumice vesicles during volcanic eruptions. The 20 Ne/ 36 Ar ratios measured in pumice reflect the initial quenching temperature, the cooling rate of the eruption column and the bubble's wall thickness. The final Ne amount is likely to be proportional to the volume of preserved vesicles in pumice. Calculations indicate that the fraction of isolated vesicles are less than 10% of the total, suggesting that a few amount of gas is preserved in pumice after deposition.

Partial pressure measurements with an active spectrometer

Partial pressure neutral gas measurements have been made using a commercial Penning gauge in conjunction with an “active spectrometer.” In prior work utilizing band pass filters and conventional spectrometers, trace concentrations of the hydrogen isotopes H, D, T and of the noble gases He, Ne, and Ar were determined from characteristic spectral lines in the light emitted by the neutral species of these elements. For all the elements mentioned, the sensitivity was limited by spectral contamination from a pervasive background of molecular hydrogen radiation. The active spectrometer overcomes this limitation by means of a digital lock-in method and correlation with reference spectra. Preliminary measurements of an admixture containing a trace amount of neon in deuterium show better than a factor of 20 improvement in sensitivity over conventional techniques. This can be further improved by correlating the relative intensities of multiple lines to sets of reference spectra.

Electron scattering by Ne, Arand Kr at intermediate and high energies,0.5-10 keV

Semi-empirical total cross sections for electron scattering of noble gases (Ne, Ar and Kr) in the energy range 0.5-10 keV have been obtained by combining transmission-beam measurements for impact energies up to 6 keV with an asymptotic behaviour at higher energies according to the Born-Bethe approximation. The influence of the forward electron scattering on the experimental system has been evaluated by means of a Monte Carlo electron transport simulation. Theoretical values have also been obtained by applying the Born approximation in the case of inelastic processes and by means of an atomic scattering potential for the elastic part. The results of these calculations show an excellent agreement with the semi-empirical values in the above-mentioned energy range.

The Campos Sales meteorite from Brazil: A lightly shocked L5 chondrite fall

Abstract— The Campos Sales meteorite fell close to the town of Campos Sales in the northeastern Brazilian state of Ceará (7°2′ S, 40°10′ W) on 1991 January 31 at 10:00 P.M. (local time). Several fragments were recovered from an area estimated to be 1 × 3 km. The stone is an ordinary L5 chondrite (Fa25.0 and FS21.6) and is lightly shocked (S1). Metal phases present are kamacite, tetrataenite, and antitaenite. Noble gases He, Ne, Ar, Kr, and Xe have been analyzed in two bulk samples of Campos Sales. All exposure ages based on determination of cosmogenic 3He, 21Ne, 38Ar, 83Kr, and 126Xe abundances and on the cosmogenic 81Kr/83Kr ratio agree well, which suggests no gas loss during cosmic‐ray exposure. The cosmic‐ray exposure age is 23.3 ± 1.0 Ma, which falls in the range observed for L5 chondrites (20–30 Ma). The gas‐retention ages indicate He loss that must have occurred prior to or during ejection from the L‐chondrite parent body.

Near-threshold electron-impact excitation of the vacuum-ultraviolet resonance transitions in Ne, Ar, Kr, and Xe

Results of semirelativistic $R$-matrix calculations for electron-impact excitation of the ${(np}^{6}{)}^{1}{S}_{0}\ensuremath{\rightarrow}{\mathrm{np}}^{5}[n+1]s$ $(J=1)$ transitions in the noble gases Ne $(n=2),$ $\mathrm{Ar}(n=3),$ Kr $(n=4),$ and Xe $(n=5)$ are compared with experimental values for light polarizations and angle-integrated magnetic sublevel cross sections. The calculations focus on the near-threshold regime, where negative-ion resonances have a significant effect on the results. In light of the complexity of the structures, the agreement between theory and experiment is very encouraging. Nevertheless, further improvements in the theoretical treatment of both the target structure and the collision dynamics seem necessary.

Vibrational Deactivation of Highly Excited Hexafluorobenzene

Highly excited hexafluorobenzene (HFB) molecules in the electronic ground state were prepared by infrared multiphoton absorption by CO2 laser pumping using the P(38) line at 1029.43 cm -1 . The vibrational deactivation of the highly excited HFB by monatomic collider gases was monitored by time-resolved infrared fluorescence (IRF). Deactivation measurements were made for the noble gas colliders He, Ne, Ar, Kr, and Xe. The bulk average energy transferred per collision, 〈〈¢E〉〉, for these colliders was found to increase from He through to Ar; however it subsequently decreased from Ar through to Xe. This is different than the trend found in the quasiclassical trajectory calculations by Lenzer et al., which predict a decrease in the average energy transferred per collision from He to Ar to Xe. (Calculations were not reported for Ne and Kr.) However, similar trends in related energy-transfer parameters have been reported for the deactivation of C 6F14 and C8F18 by the same series of five noble gases. A comparison is made with previous experimental measurements for the colliders He and Ar which were obtained using UV excitation of the HFB. For the same monatomic colliders, the 〈〈¢E〉〉 values for HFB are much greater than those for the closely related aromatics, benzene, toluene, and pyrazine.

Noble gases in pillow basalt glasses from the northern Mariana Trough back-arc basin

Noble gas concentrations and isotopic compositions have been measured in eight samples of pillow basalt glasses collected from seven different localities along 250 km of the Mariana Trough spreading and rifting axis. The samples have uniform and mid-ocean ridge basalt (MORB)-like 3He/4He values of 9–12 × 10–6 (6.4–8.6 times atmospheric) despite large variations in 4He. Concentrations of the noble gases Ne, Ar, Kr, and Xe show much smaller variations between samples, but larger variations in isotopic compositions of Ne, Ar, and Xe. Excess radiogenic 21Ne is observed in some samples. 40Ar/36Ar varies widely (atmospheric to 1880). Kr is atmospheric in composition for all samples. Some samples show a clear excess 129Xe, which is a well-known MORB signature. Isotopic compositions of the heavier noble gases (Ar, Kr, and Xe) in some samples, however, show more atmospheric components. These data reflect the interaction of a MORB-like magma with an atmospheric component such as seawater or of a depleted mantle source with a water-rich component that was probably derived from the subducting slab.

Dissolved gas dynamics in perennially ice‐covered Lake Fryxell, Antarctica

We use the concentrations of noble gases (He, Ne, and Ar), helium isotopes, and tritium to characterize the mechanisms and rates of ventilation for Lake Fryxell, Antarctica, as well as the physical processes controlling dissolved gases. The upper oxic zone is ventilated on timescales of several decades. The anoxic bottom waters are weakly ventilated, with a turnover time of ∼3,800 years. In the upper euphotic zone, helium and neon are greatly undersaturated with respect to solubility equilibrium with the atmosphere, whereas argon is greatly supersaturated owing to equilibrium partitioning of the gases between ice, water, and air inclusions in the ice. In the bottom waters, the inert dissolved gas concentrations may be remnants of a near‐desiccation event that occurred ∼2,000 years B.P., consistent with current paleoclimatic theories.

Incorporation of Helium into Endohedral Complexes of C60 and C70 Containing Noble-Gas Atoms: A Tandem Mass Spectrometry Study

Endohedral complexes of fullerenes and noble-gas atoms were originally prepared by a mass spectrometric method involving high-energy collisions of fullerene ions and noble-gas targets and, following that, by a high-pressure, high-temperature method involving neutral fullerenes and a noble gas as reactants. The latter method has made available sufficient quantities of the endohedral complexes of C60 and C70 with the various noble gases (He, Ne, Ar, and Kr) that the tandem mass spectrometric method can be used to test the possibility of preparing a new class of endohedral complexes that contain two noble-gas atoms. These new capture complexes do indeed form upon activation of the radical cation of the noble-gas endohedral complex by high-energy collisions with helium atoms. These complexes then decompose to give equivalent parallel losses of C2 units accompanied by expulsion of none, one, or both of the captured noble-gas atoms. The capture event causes the gain in excess of 34 eV of additional internal energy, but the capture complexes survive on the time scale (∼50 μs) for the transit through the tandem mass spectrometer. Their survival, along with their fragmentation characteristics, is consistent with formation of an endohedral complex containing both noble-gas atoms although the fullerene cage may now be distorted especially when the fullerene is C60. By analogy with the properties of empty fullerene and endohedral metallofullerene complexes, end points exist for the equivalent number of C2 units that can be expelled to give a closed-structure product that contains either one or two noble-gas atoms. These end points correlate directly with the sizes of the fullerene and the noble-gas atom(s), giving support to our conclusion that endohedral complexes containing two noble gases can be prepared.

Noble Gas Induced Pressure Broadening in the ν3, ν2+ ν3− ν2, and 2ν2Bands of NO2

Experimental results on the pressure broadening of NO2for collisions with the noble gases He, Ne, Ar, Kr, and Xe are presented. The broadening coefficients of six lines in the ν3band near 1616.85 cm−1with quantum numbers 2 ≤N″ ≤ 44, 1 ≤K″a≤ 5, and of seven lines in the ν2+ ν3− ν2band with 29 ≤N″ ≤ 36, 0 ≤K″a≤ 5, and of one line from the 2ν2band withN″ = 38,K″a= 5 are measured using a tunable diode laser spectrometer. The experimental values for lines with smallerN″ for the ν3band extend previous experimental data to analyze the dependence of the broadening coefficients on the quantum numbersN″ andK″a. Summarizing the available experimental data one can state that for collisions with helium, neon, and argon neither a clearN″ nor aK″adependence is observable. For the krypton and xenon broadening coefficient a weak decrease with increasingN″ was found. Due to the restricted quantum number range of lines in the hot band and the overtone band the quantum number dependence could not be discussed. The range of values for the present measurements is consistent with previous measurements on the ν3fundamental band.

Index of refraction of noble gases for sodium matter waves.

We present a theoretical study of the index of refraction of the light noble gases He and Ne for the propagation of sodium matter waves. Our approach is based on the well known multiple scattering theory inside a medium, which leads to an approximation for the index of refraction that depends only on the single forward scattering amplitude and the density distribution functions for the atoms of the medium. The forward scattering amplitude between a sodium atom and a noble gas atom is calculated from molecular potential curves using the eikonal approximation. An explicit phase space average is performed over the noble gas atom distribution in the medium. Our results show very good agreement with the recent interferometry measurements of Schmiedmayer et al. [Phys. Rev. Lett. 74, 1043 (1995)]. Our calculations provide an interpretation of the experimental data, and may shed some light on possibilities for obtaining improved interatomic potentials through atomic interferometry measurements. \textcopyright{} 1996 The American Physical Society.

Theoretical calculation of transport properties of the noble gases He and Ne and their binary mixtures at low density

Using the Tang-Toennies potential model and a set of expressions given by J. Kestinet al., we calculate the transport properties of the two noble gases He and Ne and of their binary mixtures, based upon the calculation of the interaction potential. Our calculated results for the transport properties are restricted to low densities but cover the full temperature interval extending from 50 K to the onset of ionization; the mole fraction of the binary mixtures isx1:x2=0.25:0.75. Our results are comparable to the best theoretical results given by J. Kestinet al.