Is it possible to synthesize organic Ar compound? a theoretical study

The currently synthesized noble gas (Ng) molecules are mostly xenon or krypton compounds. HArF is the only experimentally prepared compound containing a light Ng atom. In this work, a new argon compound with the formula HArC₄CN, was predicted to be theoretically stable (5.66 kcal/mol at ROCCSD(T)/6-311++g(2d,2p) level of theory). Two decomposition transition states were found, i.e. the 3-body and 2-body decomposition, which produces H, Ar and C₄CN or HC₄CN and Ar respectively. The HArC4CN molecule is meta-stable, but the low energy barrier between the stable molecule and the 3-body transition state makes it possible to synthesize from the three fragments and the high energy barrier between the minimum and the 2-body transition state prevented it from decomposing. Natural bond orbital (NBO) and electron localization function (ELF) analysis show a strong ionic bond between Ar and C atoms whereas covalent between Ar and H. Compared with previous work, it is the conjugation effect of ?C₄CN as well as the its electronegativity that activates the noble gas atom and results in a stable noble gas compound.     

Output power saturation in high current regions of different noble-gas ion lasers

Detailed experiments with cw noble gas ion lasers in high current regions are reported. Optimum lasing conditions and saturation behaviour of individual laser transitions in singly and doubly ionized argon, krypton, and xenon have been investigated. Various saturation mechanisms are discussed, such as resonance-radiation trapping, collisional deexcitation, multiple ionization, radial and axial gas pumping, and optical degradation of the cavity mirrors. The experimental results indicate that resonanceradiation trapping is the most probable cause of power limitation in noble-gas ion lasers.     

A long-pulse xenon ion laser as a pumping source for dye lasers

A simple xenon ion laser that is either sealed or has a gas flow mode is described. The laser delivered long pulses ( 15 μs) of almost 1 kW peak power. It has been used to pump a dye laser employing the same configuration as cw dye lasers. The system is inexpensive and can be mode-locked, enabling it to yield ultrashort pulses comparable in duration to those delivered by cw argon laser-pumped dye lasers but with much higher peak powers.     

Die Reaktion54Xe(n, α)52Te mit Neutronen der Energie 12,5 bis 18,0 MeV

The reaction₅₄Xe(n, α)₅₂Te was investigated in the neutron energy range 12.5 to 18.0 MeV. A high pressure gas scintillator filled either with pure xenon of natural isotopic abundance or with a mixture of xenon and helium was used as a target and as a detector simultaneously. The helium served as a monitor, (n, α)-spectra were measured and analyzed by evaporation theory. Large components of direct processes were found. The level density parameter of⁵²Te was determined as (17.0±1.7) MeV^?1. The cross section excitation function is given as well as the branching ratios for evaporation and direct processes as a function of neutron energy.     

A simulation toolkit for electroluminescence assessment in rare event experiments

A good understanding of electroluminescence is a prerequisite when optimising double-phase noble gas detectors for Dark Matter searches and high-pressure xenon TPCs for neutrinoless double beta decay detection.A simulation toolkit for calculating the emission of light through electron impact on neon, argon, krypton and xenon has been developed using the Magboltz and Garfield programs. Calculated excitation and electroluminescence efficiencies, electroluminescence yield and associated statistical fluctuations are presented as a function of electric field. Good agreement with experiment and with Monte Carlo simulations has been obtained.     

High-intensity femtosecond laser absorption by rare-gas clusters

The energy absorption efficiency of high-intensity (～10^{16}W/cm^2) femtosecond laser pulses in a dense jet of large rare-gas clusters has been measured. Experimental results show that the energy absorption efficiency is strongly dependent on the cluster size and can be higher than 90%. The measurement of the ion energy indicates that the average ion energies of argon and xenon can be as high as 90 and 100keV, respectively. The dependence of the average energy of the ions on the cluster size is also measured. At comparatively low gas backing pressure, the average ion energies of argon and xenon increase with increasing gas backing pressure. The average ion energy of argon becomes saturated gradually with further increase of the gas backing pressure. For xenon, the average ion energy drops a little after the gas backing pressure exceeds 9 bar (3.2×10^5 atoms/cluster). The result showing the existence of a maximum average ion energy has been interpreted within the framework of the microplasma sphere model.     

A mass spectrometric line for tritium analysis of water and noble gas measurements from different water amounts in the range of microlitres and millilitres

This paper describes the procedure followed for noble gas measurements for litres, millilitres and microlitres of water samples in our laboratory, including sample preparation, mass spectrometric measurement procedure, and the complete calibrations. The preparation line extracts dissolved gases from water samples of volumes of 0.2 μ l to 3 l and it separates them as noble and other chemically active gases. Our compact system handles the following measurements: (i) determination of tritium concentration of environmental water samples by the ³He ingrowth method; (ii) noble gas measurements from surface water and groundwater; and (iii) noble gas measurements from fluid inclusions of solid geological archives (e.g. speleothems). As a result, the tritium measurements have a detection limit of 0.012 TU, and the expectation value (between 1 and 20 TU) is within 0.2 % of the real concentrations with a standard deviation of 2.4 %. The reproducibility of noble gas measurements for water samples of 20–40 ml allows us to determine solubility temperatures by an uncertainty better than 0.5 °C. Moreover, noble gas measurements for tiny water amounts (in the microlitre range) show that the results of the performed calibration measurements for most noble gas isotopes occur with a deviation of less than 2 %. Theoretically, these precisions for noble gas concentrations obtained from measurements of waters samples of a few microlitres allow us to determine noble gas temperatures by an uncertainty of less than 1 °C. Here, we present the first noble gas measurements of tiny amounts of artificial water samples prepared under laboratory conditions.     

Measurement of neutral gas temperature in inductively coupled plasmas

Dependence of the neutral gas temperature on the gas pressure and discharge power in an inductively coupled plasma source has been investigated using optical emission spectroscopy. Both nitrogen and argon plasmas have been studied separately. In the case of argon plasma, about 5% nitrogen was added to the total gas flow as an actinometer. The maximum temperature was found to be as high as 1850 K at 1 Torr working pressure and 600 W radiofrequency power. The temperature increases almost linearly with the logarithm of the gas pressure, but changes only slightly with the discharge power in the range of 100–600 W. In a nitrogen plasma, a sudden increase in the neutral gas temperature occurs when the gas pressure is increased at a given discharge power. This suggests a discharge-mode transition from the H-mode (high plasma density) to the E-mode (low plasma density). In the H-mode, the gas temperature is proportional to the logarithm of the gas pressure, as in the argon plasma. However, the gas temperature increases almost linearly with the discharge power, which is in contrast to the case of argon plasma. The electron density in the nitrogen plasma is about 10% of that in the argon plasma. This may explain the observation that the nitrogen neutral temperature is always lower than the argon neutral temperature under the same discharge power and gas pressure.     

Host–guest and guest–guest interactions in noble gas hydrates

The encapsulation of noble gas atoms, helium, neon, argon and krypton in dodecahedral (DD) and its fused cages is studied using the dispersion corrected density functional theoretical method employing B97-D functional and cc-pVTZ basis set. The influence of an adjacent cage and the presence of a guest atom therein on the host–guest and the guest–guest interactions in noble gas hydrates are investigated. It is revealed that the host–guest interaction increases with an increase in the size of the encapsulated atom. The feasibility of encapsulation of guest species is analysed in terms of change in enthalpy (?H) and Gibbs free energy (?G). The results indicate that Kr@DD is stable at a relatively high temperature and low pressure (260 K, 1 atm), whereas the encapsulation of Ne and Ar at the same temperature requires high pressure (～100 atm). It is also found that the values of ?H and ?G for the encapsulation do not depend on the presence of an adjacent cage or the guest species trapped in the neighbouring cavity.     

Heat flux between parallel plates through a binary gaseous mixture over the whole range of the Knudsen number

The heat flux problem for a binary gaseous mixture confined between two parallel plates with different temperatures is studied on the basis of the McCormack kinetic model equation, which was solved by the discrete velocity method. The calculations were carried out for three mixtures of noble gases: neon–argon, helium–argon and helium–xenon. The heat flux and distributions of temperature, density and concentration were calculated for several values of rarefaction in the range from 0.01 to 40 and for three values of the concentration: 0.1,0.5$0.1,0.5$ and 0.9$0.9$. The numerical data together with an analytical solution based on the temperature jump boundary condition cover the whole range of the gas rarefaction beginning from the free-molecular regime to the hydrodynamic one. It was shown that the heat flux significantly depends on the intermolecular interaction law.     

Generation of short-pulse VUV and XUV radiation

Starting from intense short-pulse KrF (248 nm, 25 mJ, 400 fs), ArF (193 nm, 10 mJ, 1 ps), and Ti:sapphire (810 nm, 100 mJ, 150 fs) laser systems, schemes for the generation of fixed-frequency and tunable VUV and XUV radiation by nonlinear optical techniques are investigated. With the KrF system, a four-wave mixing process in xenon yields tunable radiation in the range of 130–200 nm with output energies of, so far, 100 J in less than 1 ps. For the XUV spectral range below 100 nm, nonperturbative high-order harmonic generation and frequency mixing processes in noble gas jets are considered. To achieve tunability, the intense fixed-frequency pump laser radiation is mixed with less intense but broadly tunable radiation from short-pulse dye lasers or optical parametric generator-amplifier systems. In this way, tunability down to wavelengths of less than 40 nm has been demonstrated.     

Pressure broadening of the oxygen λ5577 Å line by rare gas

We report on measurements of collision broadening of the electric quadrupole transition λ5577.35 Å in oxygen by argon, krypton and xenon. The broadening constant (linewidth added per unit atom density) was found to be: (4.3 ± 2.3) × 10^-21 cm^-1 atom^-1 cm³ for argon (reported earlier), (8.0 ± 1.7) × 10^-21 cm^-1 atom^-1 cm³ for krypton, and (10.0 ± 2.0) × 10^-21 cm^-1 atom^-1 cm³ for xenon. We discuss some experimental problems associated with these measurements.     

NMR study of the dissolution of laser-polarized xenon

NMR of laser-polarized xenon is used to probe the dissolution behaviour of the noble gas in different liquids. The dissolution and self-relaxation rates are extracted via a macroscopic model, and comparison of the decay rate of the xenon magnetization in deuterated and non-deuterated solvent pairs allows the determination of the pure dipole-dipole contribution to relaxation. A transient convective effect, tentatively assigned to the xenon concentration gradient, is observed and characterized by diffusion encoding MRI experiments. The flow of xenon penetrates inside the solvent near the walls of the NMR tube, the longitudinal images showing a “” shape, the transverse ones a “O” shape. This convection effect has implications for delivery conditions of laser-polarized xenon in continuous flow experiments and magnetic resonance imaging. Received 29 April 2002 / Received in final form 26 July 2002 Published online 22 October 2002 RID="a" ID="a"e-mail: hdesvaux@cea.fr RID="b" ID="b"URA CNRS/CEA 331     

DC magnetron sputtered tungsten: W film properties and electrical properties of W/Si Schottky diodes

Deposition of metallic tungsten (W) thin films on silicon substrates has been carried out using dc magnetron sputtering in argon or xenon gas. The deposition of W films was investigated at various working gas pressures, while the entire deposited W films were obtained at fixed power. The stress, resistivity, and structure of the W films were systematically determined as a function of the pressure of both argon and xenon. A compressive-to-tensile stress transition is observed as the working gas pressure is increased. The transition occurs at a critical pressure and coincides with a significant decrease of the grain size and an increase of the W-film resistivity. The stress transition of W-sputtered films with argon is associated with the transformation of -W phase into -W phase. The films deposited in xenon always exhibit the -W structure. In addition, a change in the Schottky barrier height (SBH) on n-type silicon of about 40±10 meV is observed at the critical pressure. On the other hand, the barrier height on the p-type silicon remains constant under all the experimental conditions investigated. These last results indicate that the Fermi level at the interface is pinned with respect to the valence band edge. The observed variation of the barrier height on n-type Si is discussed in terms of defects, change of the work function of the metal (W), and modification of the band gap of Si. PACS 72.20.-i; 73.30.+y; 73.20.-m     

The infrared spectrum of C2F5Cl in cryogenic matrices

We have measured the infrared spectrum of pentafluoroethyl chloride in cryogenic matrices of argon, nitrogen, krypton, and xenon from 880 to 1360 cm^?1. Numerous combination bands were observed; assignments and symmetries are reported for most. Appreciably more structure was observed in argon than in other matrices. The observed splitting of the fundamental bands in an argon matrix into two or more components may be due to multiple trapping sites.     

Applications of the 308-nm excimer laser in dermatology

Excimer lasers contain a mixture of a noble inert gas and a halogen, which form excited dimers only in the activated state. High-energy current is used to produce these dimers, which have a very short lifetime, and after their fast dissociation they release the excitation energy through ultraviolet photons. The application of these lasers proved to be successful in medicine, including the field of ophthalmology, cardiology, angiology, dentistry, orthopaedics, and, in recent years, dermatology. For medical purposes, the 193-nm argon fluoride, the 248-nm krypton fluoride, the 351-nm xenon fluoride, and the 308-nm xenon chloride lasers are used. Recently, the 308-nm xenon chloride laser has gained much attention as a very effective treatment modality in dermatological disorders. It was successfully utilized in psoriasis; later, it proved to be useful in handling other lightsensitive skin disorders and even in the treatment of allergic rhinitis. This review summarizes the possible applications of this promising tool in dermatology.     

Méthode d’épuration des gaz rares au moyen de décharges électriques de haute fréquence

Raw krypton and xenon gases obtained from the distillation of air contain impurities such as CF₄ and CH₄, which preclude their use in many applications. These impurities can be abated by having the gas circulating through a microwave-sustained electric discharge. The use of this technique for production proves to be beneficiai in terms of energy consumption, reduction of gas losses, easiness and safety of operation. Plasma purification is therefore an useful extension of the range of available technologies for the design of high performance pure krypton/xenon production plants. It further demonstrates the feasibility and interest of achieving selective chemistry in a plasma that is not in thermodynamic equilibrium.     

Narrowing and broadening parameters for H2O lines perturbed by helium,argon and xenon in the 1170–1440 cm−1 spectral range

Collision effects on water vapor at low concentration in a mixture with noble gases (helium, argon and xenon) have been studied by Fourier transform spectroscopy in the pressure range where line narrowing by dynamic confinement (Dicke effect) and collision broadening are observable, i.e. when the Voigt function cannot reproduce the observed profiles. Precise values of the broadening parameter have been obtained for the P and Q branches of the H₂O ν ₂ band taking into account molecular confinement (hard or soft collisions). The broadening parameter value derived from a Voigt profile for H₂O lines perturbed by helium is smaller by about 10% than values determined using the soft or hard collision model. For H₂O lines perturbed by argon or xenon this difference can reach more than 50% for the narrowest lines.     

Hyperpolarized (131)Xe NMR spectroscopy

Hyperpolarized (hp) (131)Xe with up to 2.2% spin polarization (i.e., 5000-fold signal enhancement at 9.4 T) was obtained after separation from the rubidium vapor of the spin-exchange optical pumping (SEOP) process. The SEOP was applied for several minutes in a stopped-flow mode, and the fast, quadrupolar-driven T(1) relaxation of this spin I = 3/2 noble gas isotope required a rapid subsequent rubidium removal and swift transfer into the high magnetic field region for NMR detection. Because of the xenon density dependent (131)Xe quadrupolar relaxation in the gas phase, the SEOP polarization build-up exhibits an even more pronounced dependence on xenon partial pressure than that observed in (129)Xe SEOP. (131)Xe is the only stable noble gas isotope with a positive gyromagnetic ratio and shows therefore a different relative phase between hp signal and thermal signal compared to all other noble gases. The gas phase (131)Xe NMR spectrum displays a surface and magnetic field dependent quadrupolar splitting that was found to have additional gas pressure and gas composition dependence. The splitting was reduced by the presence of water vapor that presumably influences xenon-surface interactions. The hp (131)Xe spectrum shows differential line broadening, suggesting the presence of strong adsorption sites. Beyond hp (131)Xe NMR spectroscopy studies, a general equation for the high temperature, thermal spin polarization, P, for spin I ≥ 1/2 nuclei is presented.     

Pulsed-Field-Gradient Measurements of Time-Dependent Gas Diffusion

Pulsed-field-gradient NMR techniques are demonstrated for measurements of time-dependent gas diffusion. The standard PGSE technique and variants, applied to a free gas mixture of thermally polarized xenon and O₂, are found to provide a reproducible measure of the xenon diffusion coefficient (5.71 × 10⁻⁶m²s⁻¹for 1 atm of pure xenon), in excellent agreement with previous, non-NMR measurements. The utility of pulsed-field-gradient NMR techniques is demonstrated by the first measurement of time-dependent (i.e., restricted) gas diffusion inside a porous medium (a random pack of glass beads), with results that agree well with theory. Two modified NMR pulse sequences derived from the PGSE technique (named the Pulsed Gradient Echo, or PGE, and the Pulsed Gradient Multiple Spin Echo, or PGMSE) are also applied to measurements of time dependent diffusion of laser polarized xenon gas, with results in good agreement with previous measurements on thermally polarized gas. The PGMSE technique is found to be superior to the PGE method, and to standard PGSE techniques and variants, for efficiently measuring laser polarized noble gas diffusion over a wide range of diffusion times.