Light Rare Gases Research Articles

Protonated Clusters of Neon and Krypton

We present a study of cationic and protonated clusters of neon and krypton. Recent studies using argon have shown that protonated rare gas clusters can have very different magic sizes than pure, cationic clusters. Here, we find that neon behaves similarly to argon, but that the cationic krypton is more similar to its protonated counterparts than the lighter rare gases are, sharing many of the same magic numbers.

Numerical investigation of depth profiling capabilities of helium and neon ions in ion microscopy

The analysis of polymers by secondary ion mass spectrometry (SIMS) has been a topic of interest for many years. In recent years, the primary ion species evolved from heavy monatomic ions to cluster and massive cluster primary ions in order to preserve a maximum of organic information. The progress in less-damaging sputtering goes along with a loss in lateral resolution for 2D and 3D imaging. By contrast the development of a mass spectrometer as an add-on tool for the helium ion microscope (HIM), which uses finely focussed He+ or Ne+ beams, allows for the analysis of secondary ions and small secondary cluster ions with unprecedented lateral resolution. Irradiation induced damage and depth profiling capabilities obtained with these light rare gas species have been far less investigated than ion species used classically in SIMS. In this paper we simulated the sputtering of multi-layered polymer samples using the BCA (binary collision approximation) code SD_TRIM_SP to study preferential sputtering and atomic mixing in such samples up to a fluence of 1018 ions/cm2. Results show that helium primary ions are completely inappropriate for depth profiling applications with this kind of sample materials while results for neon are similar to argon. The latter is commonly used as primary ion species in SIMS. For the two heavier species, layers separated by 10 nm can be distinguished for impact energies of a few keV. These results are encouraging for 3D imaging applications where lateral and depth information are of importance.

Substantiation of Concentration Level at Enrichment of Light Rare Gases

Dynamics of rare gases consumption is ahead of the technical capabilities of their production. Reserves of production growth of helium, neon, krypton, and xenon are associated with the expansion of the resource base. Entering of the distant sources of raw materials into the process chain dictates the decline in the share of impurities in the transported product side, improving of a single transport – production complex of gas concentrates recycling. While choosing a concentration technology and depth of treatment in each case it is necessary to take into account the distance between the source and the user of the gas feed, and the level of expenses for the creation and provision of new cryogenic technology.

A stochastic, local mode study of neon–liquid surface collision dynamics

Equations of motion for a fast, light rare gas atom passing over a liquid surface are derived and used to infer the dynamics of neon collisions with squalane and perfluorinated polyether surfaces from experimental data. The equations incorporate the local mode model of a liquid surface via a stochastic process and explicitly account for impulsive collisional energy loss to the surface. The equations predict angular distributions for scattering of neon that are in good quantitative agreement with experimental data. Our key dynamical conclusions are that experimental angular distributions derive mainly from local mode surface topography rather than from structural features of individual surface molecules, and that the available data for these systems can be accounted for almost exclusively by single collisions between neon atoms and the liquid surface.

Effect of Excited Particles on Electron Production in Rare Gas RF Breakdown

The characteristics of rare gas RF (13.56 MHz) breakdown are investigated, focusing our interest on the effect of excited particles on electron production specifically. First of all the pressure dependence of breakdown voltage, the breakdown voltage curve, is measured in parallel plate capacitively coupled RF discharge devices for four rare gases, He, Ne, Ar and Kr. For Ar and Kr typical well-known V-shaped type curves composed of the left and right branches are obtained, while for light rare gases, He and Ne, the L-shaped ones which show flat characteristics over a considerably broad range of pressure in the right branch are obtained. According to the similarity law for pd (p: pressure; d: electrode separation) which holds roughly in the right branch for any gases studied here, it is found that the breakdown voltage in the right branches of light gases increases with pressure through three regions, namely the gradual increase one, the flat one and the abrupt increase one. The numerical results by Kihara's breakdown criterion and the conventional Boltzmann analysis are as follows: as the working pressure increases, the dominant electron production process in the right branches of light gases shifts from the direct ionization which is the main electron production process in heavy rare gas breakdown, to the processes accompanied by excited particles and the flat region in the breakdown curve corresponds to the transition region of the dominant electron production process.

Excitation Behavior of Rare Gases in Low-Energy Plasma

Heavy rare gases like Xe have the highest abundance as fission products formed with dependence on the burnup of nuclear fuels. The interaction between heavy rare gases and low-energy electrons excited by the irradiation effect is very important for understanding the gas release mechanism and for developing the collecting method of radioactive fission product gases. Two types of plasma-testing apparatuses for the opened and closed low-energy plasmas were arranged using the radio frequency exciting source. The excitation behavior was evaluated by measuring the density and the temperature of the excited electrons. The electron density in the opened plasma increased with increase of the ionization energy of each rare gas. However, the electron density in the closed plasma of heavy rare gases (Ar, Kr, and Xe) was enhanced nearly a thousand times higher than that of light rare gases (Ne and He). The difference was interpreted as based on the cross section for energy transfer to the low-energy electron formed by the multisputtering effect on wall surfaces in the closed plasma.

Electronic Spectroscopy of C2 in Solid Rare Gas Matrixes

Electronic spectroscopy of the C(2) molecule is investigated in Ar, Kr, and Xe matrixes in the 150-500 nm range. In the Ar matrix, the D ((1)Sigma(u)(+)) <-- ((1)Sigma(g)(+)) Mulliken band near 240 nm is the sole absorption in the UV range, whereas in the Kr matrix additional bands in the 188-209 nm range are assigned to the Kr(n)()(+)C(2)(-) <-- Kr(n)()C(2) charge-transfer absorptions. Because of the formation of a bound C(2)Xe species, the spectral observations in the Xe matrix differ dramatically from the lighter rare gases: the Mulliken band is absent and new bands appear near 300 and 423 nm. The latter is assigned to the forbidden B'((1)Sigma(g)(+)) <-- X ((1)Sigma(g)(+)) transition, but the origin of the former remains unclear. The spectral assignments are aided by electronic structure calculations at the MCSCF, CCSD(T), and BCCD(T) levels of theory and correlation consistent basis sets. A significant presence of multireference character of the C(2)Xe system was noted and a linear ground-state structure is predicted. The computational results contradict previous density functional studies on the same system.

The influence of embedded atoms, molecules, and clusters on the lifetimes of electron bubbles in large He4 droplets

The lifetimes of electrons injected into large (≈106 atoms) superfluid He4 droplets have been measured in the presence of different prior embedded rare gas atoms, their clusters, and the molecules O2, H2O, and SF6. For the light rare gas atoms Ne and Ar the lifetimes of about 6⋅10−2 s, found previously for pure droplets, are reduced to between 1–2⋅10−2 s. Single molecules with large electron affinities, such as SF6 and O2 and small clusters of H2O lead to a significant increase in the lifetimes. In the case of Kr and Xe, larger clusters with n̄&amp;gt;14 are needed before the lifetimes increase. A simple model, which takes account of the energy levels occupied by the electrons in the corresponding molecules or the clusters, assumed to be solid, can qualitatively explain the observations.

Ordinary Chondrites: 2. Diffusion Losses of Rare Gases

Data on the isotopic abundances and ratios of light rare gases (He and Ne) in 600 ordinary chondrites are analyzed. The ratio of cosmogenic isotopes (3He/21Ne) c in ∼ 20% of the ordinary chondrites has been found to lie well below the correlation line that represents the dependence of (3He/21Ne) c on (22Ne/21Ne) c . This effect shows up most clearly in 4He r -chondrites, particularly in meteorites with diffusion losses of radiogenic 21Ne c , and is most likely attributable to the predominant (compared to 3He c ) diffusion losses of cosmogenic 3Hecthrough the solar heating of meteorites in orbits with small perihelion distances. This effect is enhanced by periodic variations in orbital parameters (including the perihelion distance) of meteorites throughout their exposure histories. Thermoluminescence data for ordinary chondrites confirm this scenario. The (3He/21Ne) c ratio for ∼15% of the chondrites was significantly overestimated, which may stem from the fact that such meteorites were heavily shielded in preatmospheric bodies.

Radiation trapping of the3P1−1S0resonant transitions of xenon and krypton in Xe-Kr, Xe-Ar, and Kr-Ar mixtures: Kinetic analysis and determination of the van der Waals broadening coefficients

This work concerns radiation trapping of the 123-nm krypton and 147-nm xenon lines, in the presence of a lighter rare gas, as well as the study of the decay processes of the relevant resonant states due to inelastic collisions. It deals with Kr-Ar, Xe-Kr, and Xe-Ar mixtures. Pulsed, brief selective excitation of the $\mathrm{Xe}{(}^{3}{P}_{1})$ or $\mathrm{Kr}{(}^{3}{P}_{1})$ resonant states by three-photon absorption was achieved by means of a tunable dye laser. Spectral and temporal analysis was then performed. The time resolved luminescence, filtered in the vacuum ultraviolet region, obeys a decay law described by the sum of two exponential terms which are attributed to the deexcitation of the ${}^{3}{P}_{1}$ and ${}^{3}{P}_{2}$ states. The decay constants are estimated by the maximum likelihood method applied to a Poisson statistical law. In order to correctly determine the collision rate constants, it is important to account for variations of the apparent lifetime according to the gas concentration. Analysis of both systematic experimental errors and statistical errors leads to a good estimation of the accuracy of the results obtained. For each mixture, the variation of the time constants as a function of partial pressures allows a determination of the resonance broadening coefficient and van der Waals broadening coefficient of the transition studied, as well as the two- and three-body inelastic collision rates relative to the ${}^{3}{P}_{1}$ and ${}^{3}{P}_{2}$ states. There exists no energy transfer between the two gases. For binary rare-gas mixtures, where only the heavier gas is excited, homonuclear and heteronuclear three-body reactions account for the decay of the ${}^{3}{P}_{1}$ state. Nevertheless, for the ${}^{3}{P}_{2}$ state we observe both two- and three-body collisions. In order to simulate resonance radiation trapping, a numerical method based upon Monte Carlo techniques was used. Calculations were first performed and validated for an infinite cylinder. The difference between calculation and experiment was less than 1%. Then the program was adapted to our real experimental conditions and applied to the binary mixtures studied. A good agreement was found between experiments and calculations. Furthermore, our program allows us to obtain information not easily obtained experimentally.

Volatiles (He, C, N, Ar) in mid-ocean ridge basalts: assesment of shallow-level fractionation and characterization of source composition

To document the characteristics of volatiles in the terrestrial mantle, the abundances and the isotopic ratios of carbon, nitrogen, helium, and argon have been analyzed in 45 mid-ocean ridge basalts (MORB) glasses from the Mid-Atlantic Ridge between 24°N and 36°N, the East Pacific Rise at 21°N, 13°N, and 17–19°S, the Red Sea (18–20°N), the Indian Ocean near the Triple Junction, and the central North Fiji basin. Gases were extracted by crushing and subsequently were split for purification and analysis. Static mass spectrometry was used for N, He, and Ar, and conventional dynamic mass spectrometry was used for C. The data confirm the occurrence of near-constant He isotope ratios ( 3He/ 4He = 8.53 ± 0.79 Ra; n = 36) and C isotope ratios (δ 13C = −5.2 ± 0.7‰ vs. PDB; n = 21), and of a light nitrogen component in the convective mantle. Overall, the δ 15N signature of MORB (mean δ 15N = −3.3 ± 1.0‰ vs. ATM, for samples with 40Ar/ 36Ar > 1000; n = 19) does not drastically differ from that of diamonds, some of which being presumably ≥3 Ga, and is thought to represent the nitrogen isotopic ratio of the asthenospheric mantle. A common mantle source for diamond-bearing magmas and MORB magmas is unlikely, and this similarity may imply either active exchange of volatiles between the respective mantle sources or homogeneous distribution of nitrogen isotopes in these sources during most of Earth’s history. Variations of the 4He/ 40Ar∗ ratios as well as 40Ar/ 36Ar ratios are consistent with fractional crystallization–assimilation–degassing taking place in the depth range of 3 to 6 km. The corrected average C/N of the MORB mantle is 535 ± 224, significantly higher than potential cosmochemical and geochemical end-members. C/He and C/N ratios corrected for fractional crystallization–assimilation–degassing fractionation increase with the degree of MORB enrichment (e.g., increasing K 2O/TiO 2) and are thought to reflect carbon heterogeneities in the mantle source, as a result of fractional recycling of a (fluid?) component extremely enriched in carbon (C/N > 3000). The N/ 3He ratios are less variable than the C/ 3He ratios, suggesting limited recycling of nitrogen. Such limited recycling is required to preserve a N isotope ratio in the convective mantle distinct from that of the atmosphere–hydrosphere sediments. Overall, neon, argon, nitrogen, and carbon abundances in the mantle appear to be chondritic, rather than solar, although the neon isotopic signature of the mantle indicates contribution of a solar component. This apparent discrepancy may reflect mixing between a solar-type component mostly seen at present in light rare gases and a chondritic-type component and has strong implications for the origin of terrestrial matter and the processes of their accretion.

Potential Curves for the Mg+Rn Complex Including Charge-Transfer States

The lighter rare gas complexes with Mg+ are known from both computational and spectroscopic determinations to have weakly bound 2Σ+ ground states with much more strongly bound low-lying 2Π1/2,3/2 excited states. In extensive configuration interaction calculations including large relativistic effects, we show that for Rn the picture is dramatically different with strongly avoided crossings in the 2Π curves due to charge-transfer states. The avoided crossings leave the 2Π states much more weakly bound. It was found that the lowering of the Rn ionization potential relative to Xe, producing the low-lying states, can be attributed almost entirely to the large spin−orbit splitting of the Rn+ 2P states. Variations in crossing interactions are readily explained in terms of two-component spinors.

Noble gases as trace elements in magmatic processes

The abundance and isotopic composition of the trace amounts of noble gases found in magmas provide insights into the large-scale differentiation of the Earth, the origin of the atmosphere, and potentially into the degassing and differentiation of mantle-derived magmas. Unlike most other trace elements whose behavior can be understood from consideration of crystal-melt equilibria, the noble gases may also be partitioned into a magmatic vapor phase. This complicates the interpretation of observed variations in noble gas abundances in magmas, but it also means that noble gas abundances can yield information not obtainable from geochemical studies of non-volatile trace elements (e.g., regarding magma degassing history). Currently available data and theoretical models allow reasonably comprehensive description of how noble gas partitioning between melt and vapor will vary with melt composition, pressure, temperature and the size of the noble gas atom. Partitioning of noble gases between crystals and melt or vapor is not so well understood, and the few data available are contradictory. Some studies suggest that noble gases are highly incompatible in crystals ( D < 0.01), while others suggest that crystal-liquid partition coefficients are higher ( D > 0.1), and possibly that the heavy rare gases (e.g., Kr, Xe) are more compatible than the lighter rare gases (e.g., He, Ne). Of additional concern is whether defects may play a role in allowing incorporation of electrically neutral noble gases in crystals, especially since noble gas contents of many natural crystals may be in the sub-ppb concentration range. Most data support incompatible behavior for the noble gases but complications arising from adsorption effects, especially for the heavy rare gases, possible siting of noble gases in defects, and concerns about “contamination” of samples by gas-rich fluid inclusions require additional investigation before we can quantitatively model the behavior of noble gas elements during partial melting or during crystal fractionation.

Efficient stimulated emission of ultraviolet and infrared radiation from a mixture of nitrogen and light rare gases

Electron beam excitation was used to achieve lasing simultaneously due to the 3d–4p transitions in Ar (λ = 1.79 μm) with a total efficiency of ~ 2 % and due to the 2+ system in N2 (λ = 358 nm) with an instantaneous excitation efficiency of up to 4%.

Current-voltage characteristics of a gas field ion source with a supertip

The field ionization properties of a supertip, a fine protrusion on top of a regular emitter, have been studied for hydrogen and the lighter rare gases. The parameter set included tip temperature, tip radius, gas temperature and gas pressure. Due to the local field enhancement at the supertip site, angular current intensities of 35 mu A sr-1 and values of brightness up to 1010 A cm-2 sr-1 have been obtained near the optimum temperature of the gas-tip system. At temperatures below this, the gas density reaches values typical for a condensed phase. In geometrical proportion, the regular tip area appears to serve as a gas supply for the supertip current

Laser utilizing the 2+nitrogen system with excitation powers up to 20 kW/cm3

An investigation was made of the inversion kinetics in the 2+ N2 system in electron-beam-excited mixtures of nitrogen and light rare gases. Fast charge exchange processes of atomic He+ and Ne+ ions with Ar in three-body collisions were discovered. Lasing was obtained at λ = 358 nm for periods of up to 0.7 μs and with an efficiency of ~ 1% in an N2–Ar–He mixture, and an instantaneous efficiency of more than 2% was obtained for lasing duration of 250 ns in an N2–Ar–Ne–He mixture. The results indicated that it should be possible to build an efficient pulse-periodic laser utilizing the 2+ nitrogen system and emitting pulses of 200–300-ns duration.

Vibrational effects in desorption of light rare gases from metals

The angle-resolved thermal desorption flux for Ne-Cu(111) has been computed at 5, 10 and 15 K in the Distorted Wave Born Approximation using an accurate microscopic description of the surface lattice dynamics, and a realistic gas-solid potential. The angular distribution narrows as the temperature is lowered, being broader than the equilibrium theory cosine law at 15 and 10 K and narrower than it at 5 K. The Time-of-Flight spectra of the desorbed atoms are also analysed.

Pseudopotential SCF/CI calculations for the potential energies of the MHe and MNe (M=Mg, Cd, Hg) systems

Pseudopotential SCF/CI calculations have been performed for the adiabatic potentials of the group II metal (M)+light rare gas (RG) atom complexes. Semi-empirical l-dependent pseudopotentials are used which describe the interaction of the M valence electrons with both the M2+ core and RG atoms. Dipole polarisation of the M2+ core (including core-valence correlation) is explicitly taken into account. Direct and indirect relativistic effects on valence-electron orbitals are incorporated into the pseudopotentials. Spin-orbit coupling has been treated approximately. Valence-electron correlation is accounted for by CI treatment. The GTO basis sets with contraction are used in the calculations. The e -RG interaction involves both the dipole and the quadrupole polarisation terms.

Laser studies of near-resonant state-changing collisions of calcium (4s6s 1S0) with the rare gases.

State-changing collisions of Ca(4s6s ${}^{1}$${S}_{0}$) with the rare gases are studied by pulsed laser excitation and time- and wavelength-resolved detection. The total depletion rates of the 4s6s ${}^{1}$${S}_{0}$ state with different rare gases vary by over a factor 10, with the lighter rare gases being markedly more efficient than the heavier ones. Relative branching ratios to the specific near-resonant, energy-transfer product states, 4p4p ${}^{1}$${D}_{2}$ (\ensuremath{\Delta}E=-29 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), 3d4p ${}^{1}$${F}_{3}$ (\ensuremath{\Delta}E=152 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), and 4s6s ${}^{3}$${S}_{1}$ (\ensuremath{\Delta}E=216 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$), are measured for $^{3}\mathrm{He}$, $^{4}\mathrm{He}$, Ne, and Xe. Transfer to the $^{1}\mathrm{D}_{2}$ state is always the major relaxation pathway. The rate constant for $^{3}\mathrm{S}_{1}$ production is immeasurably small, implying a small spin-orbit matrix element for curve crossing that leads to a spin change. The results for 4p4p ${}^{1}$${D}_{2}$ production are compared with simple theoretical calculations based on established models for near-resonant energy transfer between states which are coupled at large internuclear distance. These models successfully explain the dominant transfer to the 4p4p ${}^{1}$${D}_{2}$ state and the trends with rare gas, which are attributed largely to enhancement of the near-resonant-transfer process with increasing velocity. The effects of wave-function mixing in the isolated atom (e.g., spin mixing) on the general outcome of state-changing collisions in two-electron atoms are discussed. Two-electron atoms offer numerous possibilities for further testing of theories of near-resonant energy transfer.

Enhancement and quenching of photoionization in rare gas mixtures

Admixing a sufficient amount of a light rare gas to a heavier rare gas effects the photoionization current measured at the absorption lines of the latter. This current is enhanced if hv > E c and quenched if hv < E c where hv is the energy of the exciting photons. E c is approximately equal to the ionization potential of the corresponding heteronuclear van der Waals molecule. Both homonuclear and heteronuclear dimer ion formation are discussed.