Emission from impurity molecular centres in binary solutions of inert crystals

The structure of impurity excitations in solid binary solutions XeKr, XeAr, KrAr has been studied using the luminescence vacuum u.v. spectroscopy. Emission from biatomic heteronuclear molecules of inert elements was separated. The existence of two excited states of heteronuclear molecules of different atomic configurations is predicted. The pair potential of inert element interaction in the excited and ground states are analysed and force constants found. The peculiarities of the heteronuclear molecule formation as a function of concentration and temperature for solid binary solutions of inert gases have been discussed.     

Plasma line emission during single-bubble cavitation

Emission lines from transitions between high-energy states of noble-gas atoms (Ne, Ar, Kr, and Xe) and ions (Ar(+), Kr(+), and Xe(+)) formed and excited during single-bubble cavitation in sulfuric acid are reported. The excited states responsible for these emission lines range 8.3 eV (for Xe) to 37.1 eV (for Ar(+)) above the respective ground states. Observation of emission lines allows for identification of intracavity species responsible for light emission; the populated energy levels indicate the plasma generated during cavitation is comprised of highly energetic particles.     

Excimer radiation from Na—Noble-gas and K—Noble-gas molecules

Emission bands from Na-noble-gas (and K-noble-gas) molecules, due to transitions between the 4sσ (and 5sσ) bound excited states and dissociating ground states, are observed. The noble gases used are Ar, Kr and Xe. The red shift of the emission band from the forbidden atomic s-s transition is largest for NaXe, for which it is 3055 cm^?1. This NaXe band may be useful as an excimer laser source, tunable from 4280 Å to 4500 Å.     

A new laser concept for isotopically selective analysis of noble gases

A new laser approach for the isotopically selective analysis of noble gases is presented. This approach uses noble gas atoms prepared in the 1s ⁵ metastable state. Hyperfine levels in the 1s ⁵ and 2p ⁹ states form two-level systems in Ne, Ar, Kr, and Xe which can be excited by a commercially available single-frequency laser system. Absorption of photons from such a laser, and the resulting momentum transfer, can be used to selectively deflect the desired isotope from a supersonic atomic beam into a detection area. Light from the same laser can then be used to selectively count atoms of the desired isotope using the photon-burst technique. Thus, enrichment and selective detection are accomplished with a single laser in a single pass through the apparatus.The problem of analyzing for⁸⁵Kr in a sample of noble gases extracted from the air is examined in detail. This is a stringent test of the selectivity of this approach because⁸⁵Kr has the same nuclear spin, and thus similar hyperfine splittings, as naturally occurring⁸³Kr. Calculations indicate that isotopic selectivity of the new approach is easily adequate to resolve⁸⁵Kr in a 10¹⁰ excess of⁸³Kr.     

Interaction of argon with the Al(100) surface

We present a new method for calculating the interaction energy of a noble gas atom with a metallic surface. This method combines atomic structure and solid state theory techniques and is thus applicable to ground state as well as to excited states of a chemisorbed (physisorbed) atom. We present results for the dipole moment and the interaction energy of Ar onto Al(100).     

Efficient fluorescence in solid noble gases excited by 10—30 kV electrons

Fluorescent spectra and efficiency of vacuum ultraviolet generation have been investigated for solid Ar, Kr and Xe excited by 10–30 kV electrons. Overall conversion efficiency of e-beam energy into a single 7 nm wide band centered near 175 nm for Xe was measured to be 30%, indicating high intrinsic efficiency when electron backscatter is taken into account. In Ar and Kr the presence of trace amounts of O₂was found to cause energy transfer from the excimer bands to longer wavelengths.     

Absorption spectra of self-trapped exciton in condensed rare gases

Optical absorption from the self-trapped exciton (STE) to its higher excited states has been observed in solid Ar, Kr, and Xe. A new absorption peak of Ar1₂ is found. Comparison of solid, liquid and gas phase data provides evidence of the similarity of level structures of Ar1₂ and STE. Tentative assignments of the observed transitions are also made.     

Electronic structure of the self-trapped exciton in rare gas solids

The Rydberg-like series of the self-trapped exciton R₂¹ in rare gas solids (Ar, Kr and Xe) are obtained by solving the effective mass equation which incorporates different corrections, including the central cell correction. The results are in good agreement with the recent transient optical absorption data in which the electron is excited into higher excited states. The origin of the luminescence bands is interpreted by analogy with a similar structure of the self-trapped excitons in alkali halides.     

Isotopic thermal diffusion factors of the noble gases

A new set of isotopic thermal diffusion factors for Ar, Kr and Xe is reported. The data have been obtained from thermal diffusion column measurements in a column previously calibrated with Ne gas, and complete the α_T data for the binary mixtures of noble gases given previously. The results lead to the conclusion that the thermal diffusion properties of the noble gases and their mixtures are well described by the law of corresponding states first proposed by Kestin, Ro and Wakeham. It is also concluded that the calibration technique used makes the thermal diffusion column a valuable instrument for the determination of the thermal diffusion factors of isotopic and non-isotopic dilute gas mixtures.     

Ar and Kr adsorption on Ag(111)

Precise structural and thermodynamic studies of Kr and of Ar adsorbed on Ag(111) are made using low energy electron diffraction. The phase diagram, lattice constants of the unconstrained monolayer and of the monolayer in equilibrium with the bilayer, latent heats of adsorption and isosteric heats are measured. The results are similar to those of an earlier study of Xe adsorbed on Ag(111). The results are compared to model calculations using effective lateral interactions which are similar to those for Xe/Ag(111). Comparison of the results for Xe, Kr, and Ar on Ag(111) is made using corresponding states scalings. A comparison is also made with properties of the non-registry phases of Xe, Kr, and Ar on basal plane graphite.     

X@C20F20(X=He,Ne,Ar,Kr)几何结构和 电子结构的理论研究

采用密度泛函理论中的广义梯度近似, 对X@C₂₀F₂₀(X=He, Ne, Ar, Kr)几何结构和电子结构进行了计算研究. 几何结构优化发现: 惰性气体原子X内掺到C₂₀F₂₀笼后, 均稳定于碳笼中心, 随着内掺X原子序数的增大, X原子对C₂₀F₂₀笼的影响越来越大. 能隙、内掺能和振动频率计算表明: 内掺X原子使得C₂₀F₂₀的稳定性得到了显著提升, X@C₂₀F₂₀(X=He, Ne, Ar, Kr)都具有良好的稳定性, 并且随着X原子序数的增大, 其稳定性也基本呈现逐渐增强的趋势. 电子结构研究发现: X原子对X@C₂₀F₂₀费米能级附近的占据轨道基本没有贡献, 而对其未占据轨道贡献较大. 计算还发现: 在X@C₂₀F₂₀中, He 和Kr分别从C₂₀F₂₀的C 笼上获得了0.126和0.271个电子, 而Ne和Ar却分别向C笼转移了0.060和0.012个电子. 由此可见: X原子与C原子之间都发生了电荷转移, C笼上的C原子与惰性气体原子X间形成了一定的离子键.     

Hot oxygen atom ballistics on Pt(111): collisional desorption of noble gases

Hot oxygen atoms formed by ultraviolet photofragmentation of chemisorbed O₂ on Pt(111) at T_s=20 K induced collisional desorption of coadsorbed noble gases. Angular distributions of desorbing Ar, Kr, and Xe were sharply peaked at 35° from the surface normal. Mean translational energies of the noble gases were in the 0.12 eV (1400 K) range. The O atom photofragments were found to chatter between the surface and the noble gases during the desorption process. The fastest O atom photofragments produced at 250 nm had an energy of at least 0.73 eV.     

Differential cross sections for elastic scattering and positronium formation for positron collisions with Ne,Ar, Kr and Xe

Differential cross sections for elastic scattering and Ps(1s) formation are calculated in the truncated coupled-static (TCS) approximation. Comparison is made with the elastic scattering measurements of Dou et al. on Ar and Kr. There is no support from the TCS approximation for the view that structure seen in the experimental results for Ar in the energy range 55–60 eV may be due to a resonance associated with coupling to the positronium formation channel. Rather, we believe that Dou et al. are right in correlating this feature with the maximum in the ionization cross section. In the experiment on Kr structures are observed at 25 and 200 eV. It is tentatively suggested that the structure at 200 eV may be the resonance seen in the TCS calculation at 100 eV, but modified by polarization and absorption effects. It is also suggested that the feature at 25 eV could be associated with coupling to excited states of positronium. The TCS results for the Xe target predict some very pronounced behaviour which would be worth experimental investigation. TCS differential cross sections for Ps(1s) formation by capture of an electron from the outer p-shell of the atom are presented for impact energies up to 75 eV. A noticeable property of these cross sections is that they do not usually peak at the forward direction; this is consistent with an experimental observation by Laricchia et al. on He and Ar targets. The importance of also looking at electron capture from inner shells is emphasized and illustrated by the cross section for electron capture from the 3s shell of Ar.     

Ion beam induced crystal-edge nanoclusters at the origin of poly(ethylene glycol) film stabilization

PEG films stabilized by noble gas ion beam irradiation showed characteristic clustering at the crystal edges. These structures appear in determined ion beam conditions after exposure to Ar and Kr ions. Atomic force microscopy exploration indicates that, rather than presenting drastic topographic features, the nanostructures show radically different elastic properties. Within the concerned set of ion beam conditions, the surface properties are observed to vary according to the absorbed energy as suggested by X-ray photoelectron spectroscopy and contact angle measurements. These analyses predict that Ar irradiation in the 500-600 V extraction potential range is an appropriate condition for PEG stabilization.     

Simulation of above-threshold ionization experiments using the strong-field approximation

Recently performed above-threshold ionization (ATI) experiments with noble gases allow the determination of the complete energy and angular distribution of the emitted photoelectrons. In order to simulate such experiments, we have generalized our numerical code for the calculation of ATI spectra in order to achieve a realistic simulation of ATI of the noble gases He, Ne, Ar, Kr, and Xe. Our method is based on an improved version of the strong-field approximation and includes focal averaging. A semiclassical analysis of the dependence of the cutoff law on the photoelectron emission angle is presented. The effects of channel closings on the high-energy spectra are analyzed.     

Ionisation of noble gases by positron impact

The positron induced absolute single and double ionisation cross sections for the noble gases Ar, Kr and Xe have been determined in the energy region from below threshold to ∼1000 eV. With the use of an admixture of He to the target gas normalisation was performed by comparison to known single ionisation cross sections for He. Special interest has been taken in the energy gap of 6.8 eV below the direct double ionisation threshold energy, where only double ionisation with positronium formation is possible. This has been done to study the significance of double ionisation with Ps formation for the heavy noble gases. This revised version was published online in August 2006 with corrections to the Cover Date.     

100 MW, 248.4 nm,KrF laser excited by an electron beam

Laser oscillations have been observed at 248.4 nm from excited KrF molecules. The excited KrF molecules were produced by injecting an intense electron beam into mixtures of Ar, Kr and F₂. A peak power of 1.15 × 10⁸ W with a total energy of 5.6 J has been observed. Up to 3% of the deposited e-beam energy was converted to laser-energy.     

Influence of spectral line broadening on the mode structure of He-Kr and He-Ar gas lasers

Using the semiclassical perturbation approach, Stark broadening parameters for Kr II 469.4 nm, Ar II 476.5 nm, and Ar II 480.6 nm spectral lines have been determined. The obtained results have been used for the investigation of the role of the Stark broadening mechanism on the mode properties of hollow cathode excited noble gas mixture lasers. It has been found that for the He-KrII 469.4 nm laser broadening by neutral atom collisions is large enough to explain the single-mode operation of this laser, as opposed to the He-ArII 476.5 nm laser where Stark broadening also has to be taken into account to explain this property. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 405–407, May–June, 2006.     

Emission spectra for ArNe binary crystals

Emission spectra for ArNe binary crystals have been measured in the range of 6–18 eV at the Ar concentration of 0.01 – 100 mol%. Luminescence was excited by slow electrons at T = 5°K. The spectrum of excitons bound on the atomic and molecular type centres is observed. The energies of radiative transition in a crystal appear to be very close to those in a gas phase because of the relaxation processes at which the resonance exchange interaction decreases considerably. The bands of atomic centres display a fine structure which reflects the effect of the lattice crystal field of Ne. For the ArNe crystals it has been shown that excitons are not thermalized completely and there is the independent relaxation of the lowest states of various Wanier series to local excitons. A scheme for the relaxation process in argon involving the formation of a molecular centre Ar₂¹ is given.     

Ar^1^6^＋离子双激发态的新量子数描述和跃迁规律

此文采用ＣＩ方法计算了类氦Ａｒ１６＋离子双激发态能级和波函数，并向ＤＥＳＢ（Ｄｏｕｂｌｙ－ｅｘｅｃｉｔｅｄｓｔａｔｅｓｂａｓｉｓ）做投影，求出表征这些双激发态的新量子数Ｋ、Ｔ和Ａ。计算和比较了初态ｎ（ｎ－１，０）ｎ＋１Ｓｅ的辐射和Ａｕｇｅｒ跃迁率，发现辐射跃迁随初态主量子数ｎ的变化是光滑的，而Ａｕｇｅｒ跃迁则随ｎ的变化是不光滑的。