He,Ne,Ar,Kr和Xe原子电子的动量密度分布研究

对He,Ne,Ar,Kr和Xe原子体系中电子在动量空间的性质进行了系统的理论计算研究.采用自洽场HFR方法计算了坐标空间He,Ne,Kr和Xe原子体系单电子径向波函数,动量空间的单电子波函数由坐标空间原子体系单电子径向波函数通过运用傅立叶变换计算得到.在冲量近似条件下,进一步计算研究了这些原子的单电子动量密度分布和原子体系总的Compton轮廓.计算结果与已有的实验实验值和其他文献的理论计算结果比较表明,本文计算的结果是准确的.     

Formation and migration properties of the rare gases He,Ne, Ar,Kr, and Xe in nickel

The energies of formation and migration of various rare gas-point defect complexes in an f.c.c. nickel lattice have been calculated for He, Ne, Ar, Kr, and Xe. Formation energies of rare gas atoms at interstitial sites are compared with those in substitutional sites. Binding energies are presented for self-interstitials and vacancies trapped to the various rare gas substitutionals. We also present migration energies and migration paths for various rare gas interstitials and substitutionals with and without trapped vacancies and self-interstitials. The migration energies are compared with the breakup energies for the corresponding complexes. We find that divacancy-rare gas complexes are rather stable and will migrate at relatively low energies compared to other substitutional rare gas migration processes.     

Cooling efficiency in collisions between Pd and He,Ne, Ar and Kr

The cooling of the metal cluster Pd₁₃ in an atmosphere of rare gas has been studied by means of computer simulation. By simulation, the average energy transfer in collisions between one cluster and one gas atom has been obtained. Emphasis has been placed on conditions when the temperatures of the colliding species are almost equal. All modes of motion, inclusive the translation, must be considered in order to obtain vanishing energy transfer at equilibrium. A simulation scheme is presented by which the energy transfer is zero to the cluster when the gas and the cluster temperatures are equal. At equilibrium the energy transfer does however not vanish for all impact parameters. In the collisions with Pd₁₃, the cluster is heated by collisions with a small impact parameter but equally cooled by collisions with a large impact parameter. Argon and krypton are found to cool Pd₁₃ equally efficiently while neon and helium are less efficient cooling agents. Received 28 September 2001 / Received in final form 8 August 2002 Published online 12 November 2002 RID="a" ID="a"e-mail: JanW@phc.gu.se     

Long range dispersion interactions of the low lying states of Mg with H,He, Ne,Ar, Kr and Xe

The dispersion coefficients for the van der Waals interactions for the low lying states of magnesium (3s² ¹S ^e , 3s3p ³P ^o , 3s3p¹P ^o , 3s4s ³S ^e , 3s4s ¹S ^e , 3s3d ³D ^e and 3s3d ¹D ^e ) interacting with H, He, Ne, Ar, Kr and Xe are determined using sum rules of reduced matrix elements over pseudo-state representations of the atomic excitation spectra. The sets of transition matrix elements were taken from previous investigations of the van der Waals interactions of the Mg₂ dimer and an investigation of the van der Waals interaction for alkali atoms interacting with rare gases.     

Absolute Electron Impact Cross Sections for Single Ionization of Metastable Atoms of H,He, Ne,Ar, Kr,Xe and Rn

Cross sections for single ionization of metastable atoms of H, He, Ne, Ar, Kr, Xe and Rn by electrons with impact energy E (threshold < E < 200 eV) are determined using a recently developed semiclassical formula. The formula consists of an energy dependent term (classical binary encounter approximation) and a term containing the weighted sum of the squared radii of maximum charge density of the outer electron subshells (Born Bethe approximation). Although this formula was originally devised and applied for ground state atoms, a comparison of the present calculations with previous calculations and measurements indicates that this formula can also be used successfully in case of metastable atoms.     

Ne、Ar、Kr、Xe等离子体Planck和Rosseland平均不透明度的近似计算

根据平均原子模型和类氢光吸收系数，近似地计算了Ne、Ar、Kr、Xe等惰性元素高温、高密度等离子体的Planck和Rosseland不透明度。在计算线谱吸收过程中，采用了唯象方法处理线谱演化成谱带时的加宽效应及谱带重叠效应。将不透明度数据拟合成温度和密度的幂函数形式，它能够用于辐射体的数值拟合。     

The empirical Kestin model and the second order transport properties of binary mixtures of Ne,Ar, Kr and Xe

It is showed from the experimental α_T data for the dilute binary mixtures of Ne, Ar, Kr and Xe at 340 K that the law of corresponding states proposed by Kestin, Ro and Wakeham is able to predict the mentioned second order kinetic property altogether with the first order transport and thermodynamic properties of the examined mixtures.     

Electron stimulated desorption of Xe,Kr, and Ar

Electron stimulated desorption cross sections have been measured for Xe, Kr, and Ar overlayers on the Ag(111) surface. The Xe cross section is less than 10^?4 Ų; the Kr cross section is strongly temperature dependent, rising from 0.1 Ų at 10 K to 0.18 Ų at 50 K; the Ar cross section is 4 Ų and temperature independent. These results are rationalized using a model of the stimulated desorption similar to that proposed by Antoniewicz [Phys. Rev. B21 (1980) 3811], in which an atom is ionized by the incident beam, accelerates towards its image and is neutralized, desorbing only if the kinetic energy gained is greater than the neutral atom binding energy at the neutralization position. Fitting these data requires an exceedingly rapid dependence of the neutralization on distance for these slow ions. Rather than the effect of the mass on the ion velocity, the most important effect in determining the diverse behavior of the different gases is that the equilibrium position for the heavier gases is farther up the overlap repulsive potential and so in a region of more rapid neutralization. The model identifies several contributions to the isotope effect, predicting it to be temperature dependent. The results are extremely sensitive to the anharmonicity of the holding potential.     

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.     

Transitions and level lifetimes in Ne II, III, Ar II, III, Kr II, III and Xe II

Beam-foil spectra of neon, argon, krypton, and xenon have been recorded photographically with a fast spectrograph. The particle energies ranged from 150 to 750 keV. Transitions in Ne II, III; Ar II, III; Kr II, III; and Xe II have been identified. In addition, new multiples were identified in Ne II and Xe II and a number of unidentified lines were observed in neon, argon, and krypton. Characteristic intensity decays of over 170 lines were measured, giving the mean lives of ≈ 80 levels, with an estimated error of 30 per cent. Tabulation of energy levels with similar electron configurations in neon, argon, krypton, and xenon shows a definite progression to larger mean lives as the nuclear change increases.     

Radiation damage in solid butane irradiated by Xe+, Kr+, Ar+, Ne+ and He+ ions with energies below 1500 eV

Thick solid butane targets cooled at 77°K, containing known molar fractions of iodine, have been irradiated by monoenergetic rare gas ions with energies between 10 eV and 1500 eV. The nature and the importance of the fragmentation of the target molecules have been studied through the analysis of the formed organic iodides. The G values for the overall yield of organic iodides are roughly the same for the various ions investigated and they are energy-independent between 150 eV and 1500 eV. However the mode of fragmentation depends strongly on the nature of the particles, the probability of C-C bonds rupture increasing with the LET. The neutralization energy of the incoming ions is also assumed to play a part in the radiolysis of the target.     

Calculations of total ionization cross sections of Ne,Ar, Kr,and Xe atoms in the born approximation allowing for electron perturbations in the continuous spectrum

Electron impact ionization cross sections of Ne, Ar, Kr, and Xe atoms are numerically calculated. The electron perturbation in the continuous spectrum in the target field is taken into account. The matrix elements are calculated in many-electron, nonrelativistic approximation with allowance for the superposition of configurations and relaxation effect. The radial part of the electron wave function in the continuum is calculated by solving the single-configuration Hartree-Fock equation. The wave functions of electrons in the continuum are orthogonalized with respect to the core orbital functions. The calculated cross sections are compared to the experimental data and calculations made using the plane-wave Born approximation and that involving generalized oscillator strengths.     

Third virial coefficients of Ar+Kr and Kr+Xe mixtures

Third virial coefficients, calculated from the potentials of Lee, Henderson and Barker are given for Ar+Kr and Kr+Xe mixtures. The contributions of the three-body triple-dipole, dipole-dipole-quadrupole, and fourth-order triple-dipole interactions are included.     

The Features of Low-Lying States of Ne3, Ar3 and Kr3

The methods for few-body physics are introduced to extract structures of low-lying states of threeatom clusters of neon, argon and krypton. Similarities among the states have been found, and accordingly a number of rotational bands have been identified. Each band is characterized by a specific mode of internal oscillation. The decisive effect of symmetry has been emphasized.     

Thermal diffusion in binary mixtures containing molecular gases II: mixtures of N2 with He,Ne, Ar,and Kr and of CO2 with He and Ar

Expressions developed for the thermal diffusion factor, αT, for binary mixtures containing molecular species have been tested for six different atom-molecule interactions. Specifically, the interactions between N₂ and He, Ne, Ar and Kr, plus the interactions between CO₂ and He, Ar, have been examined, in each case using at least two competing modern potential energy surfaces. Detailed expressions in both the ‘total-energy-flux’ and the ‘two-flux’ representations have been developed, and the importance of the anisotropic components of the intermolecular potential energy surfaces in determining the thermal diffusion factor for such mixtures has been determined.     

Interaction of trapped metastable excited He atoms with solid noble gases,Ne, Ar and Kr,investigated by EPR

Local metastable excited states are found in Ne, Ar and Kr cryocrystals as He gas-discharge products are trapped in the growing cryocrystals. These states are detected by EPR and are interpreted as being local metastable excitednp⁵(n+1)s³P₂ atomic-type states in Ne, Ar and Kr cryocrystals. Analysis of the results allows the following explanation of the observed effect to be given. For the Ne cryocrystal the effect is interpreted as a new phenomenon: quasi-resonance transfer of excitation energy from the metastable He 2³S₁ atom trapped in a growing neon cryocrystal to the exciton energy band of the neon crystal followed by the exciton self-trapping into the 2p⁵3p state and subsequent decay, ending in the 2p⁵3s³P₂ state recorded by EPR in our experiment. In the case of Ar and Kr cryocrystals the effect is explained as being due to an internal ionization of the cryocrystals by the excitation energy of trapped metastable He atoms, which implies the formation in the cryocrytal of a Rg⁺ ion and a free electron in the conduction band, whereupon the fast (of 10^?12 s) self-trapping reaction of a hole follows: Rg⁺+Rg→Rg ₂ ⁺ . Thereafter the dissociative recombination reaction Rg ₂ ⁺ +e→Rg ₂ ^** →Rg+Rg*(³P₂) could take place.     

Totale Streuquerschnitte für den Stoß von H2, D2 und He an den Edelgasen Ne,Ar, Kr und Xe im thermischen Energiebereich

The velocity dependence of the total elastic cross section has been measured for the scattering of H₂, D₂, and He beams by Ne, Ar, Kr, and Xe gases. Velocity-selected beams were attenuated by gas in a scattering chamber. A universal detector, with a magnetic mass separator, was used in conjunction with lock-in techniques. The results are compared with quantum mechanical calculations using a Lennard-Jones-(12.6)-potential, and employing suitable averaging over experimental velocity distributions. Potential parameters are presented. These are in good agreement with those expected from other methods of measurement.     

Ab initio study of spectroscopic properties of RgCl (Rg=He,Ne, Ar,Kr) and their anions

Spectroscopic properties of HeCl, NeCl, ArCl, KrCl and their anions HeCl^?, NeCl^?, ArCl^? and KrCl^? in their ground state have been studied in detail using ab initio MP2, CCSD and CCSD(T) methods. These neutral molecules and their anions are weakly bound and their spectroscopic constants have been estimated using a method developed recently for calculating the spectroscopic constants of weakly bound molecule in Lennard–Jones potential. The net attractive force and the distance at which the net attractive force is greatest, have been calculated to get the physical picture. Most of the spectroscopic constants are first predicted. The calculated equilibrium bond length, dissociation energy and harmonic frequency agree very well with the experimental and theoretical values wherever available.     

Differential cross sections for charge transfer in collisions of He+, Ne+ and Ar+ with Kr

Differential charge transfer cross sections for collisions of He⁺, Ne⁺ and Ar⁺ with Kr were measured at collision energies below 500 eV. A remarkable fraction of these collisions (2–30 %) occurs with large momentum transfer and small impact parameters. These close collisions lead to an excitation of the product particles, the measured reaction channels are strongly endothermic. In the system Ar⁺+Kr one reaction channel may be described in terms of a curve crossing.     

Theoretical study on the complexes of He, Ne and Ar

This paper investigates the effect of basis sets through the potential energy curves(PECs) of six rare gas complexes He 2,Ne 2,Ar 2,He-Ne,He-Ar,and Ne-Ar.The coupled cluster singles and doubles method with perturbative treatment of triple excitations,doubly augmented basis sets of d-aug-cc-pVQZ,bond functions,and basis set superposition errors are employed.The diffuse function is more effective than the polarization function on describing the dissociation energy.The PECs are fitted into analytical potential energy functions(APEFs) using three expressions.It is found that all the expressions are suitable for describing the complexes of rare gases.Based on these APEFs,the spectroscopic parameters are calculated and the results are compared with the theoretical and experimental data available in the literature.