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.     

Positron transport in CF4 and N2/CF4 mixtures

Investigations on freestanding binary and ternary clusters of Fe _x Co _y Ir _z (x + y + z = 5, 6) are carried out using ab initio density functional theory techniques. The geometry, chemical order, binding energy, magnetic moment and electronic structure of the clusters are analyzed for the entire range of composition. Composition dependent structural transition is observed in the five atom clusters, while octahedral geometry prevailed in clusters with six atoms. Both the clusters show increment in binding energy with the increase in number of heterogeneous bonds. Analysis based on the chemical order parameter indicates that clusters favor mixing rather than segregation. The clusters exhibit ferromagnetic ordering and the inter-dependence of optimal cluster geometry to the magnetic moments and electronic structure is observed.     

Vacuum ultraviolet absorption spectra of aromatic molecules in solution

The absorption spectra of benzene, naphthalene, azulene, N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), pyrene, and fluoranthene were measured in liquid perfluoro-n-hexane (PFn-H) in the range 35 000–65 000 cm^?1 and in liquid n-pentane (n-Pt) in the range 35 000–59 000 cm^?1, using a 150-μm-thick cell. The absorption spectra in PFn-H show more structure than those in n-Pt and because they are extended in the Rydberg transition region may be used to separate Rydberg from core transitions in the gaseous spectra of the molecules studied. The transmission spectra for PFn-H, n-Pt, and some of the most commonly used hydrocarbon solvents are presented also.     

Vacuum ultraviolet gain measurements in optically pumped LiYF4:Nd3+

 We present measurements of the net-induced gain on the 5d–4f transition at 186 nm in LiYF₄ : Nd³⁺ optically pumped by radiation from a molecular fluorine laser. It is found that for LiYF₄ : Nd³⁺, one of a series of potential continuously tunable VUV lasers, relatively strong excited-state absorption results in net-induced loss. The prospects for VUV laser operation being realised in other rare-earth-doped fluorides is discussed. Received: 4 March 1996/Revised version: 10 July 1996     

Vacuum ultraviolet absorption spectra of dichlorosilane,dichloromethylsilane and dichlorodimethylsilane

The vapor phase vacuum ultraviolet absorption spectra of dichlorosilane, dichloromethylsilane and dichlorodimethylsilane are reported for the region from 40 000 to 83 000 cm^?1 (250-120 nm). Absorptions of these compounds are assigned as primarily Rydberg excitations of chlorine valence non-bonded electrons. The σ* ← np(SiCl) transition for these compounds is the first observed absorption and is badly overlapped with the first Rydberg absorptions. The first three ionization potentials of dichloromethylsilane were calculated to be 11.47, 11.82, and 12.28 eV using averaged term values and transition energies. The analysis of these spectra revealed that the first p and d molecular Rydberg states appear to be nearly degenerate and that these Rydberg levels are greatly destabilized with methyl substitution. The results of this study support the presence of strong d-p(SiCl) interactions. The strength of this effect is compared in dichlorosilane and dichlorodimethylsilane using an empirical relation.     

Vacuum ultraviolet absorption spectra of several group IVA tetrabromides

The vacuum UV absorption spectra of silicon, germanium and tin tetrabromide are discussed. The spectra, taken in the vapor phase in the region from 33,     

kinetic energy reflection from polycrystals bombarded with Ar+, Kr+, and Xe+ ions

When the surface of a solid is bombarded with ions a fraction of the primary energy is reemitted by ion reflection and sputtering. The contribution of ion reflection or sputtering to energy reflection is determined by the mass ratio of the bombarding ions to the target atoms.^1,2 In the case of light ions the contribution of reflected ions is dominant. Results for He⁺ and Ne⁺ bombardment were described in a previous paper.³ The present paper deals with results for Ar⁺, Kr⁺, and Xe⁺ bombardment of the same targets as investigated before.³ The energies of the mass selected bombarding ions range from 9 to 16 keV. The measurements were carried out by means of the thermic detector described in a separate paper.⁴ For the given mass ratios most of the reemitted energy is related to sputtering.     

The production of excimer molecules and excited atoms in a positive corona discharge in He/Xe(Kr)/SF6/CCl4 mixtures

Electrical and optical characteristics of a positive corona discharge in He/Xe(Kr)/SF₆/CCl₄ mixtures, which are of interest for the use in multiwavelength excimer radiation sources, are studied in the needle-grid electrode configuration. The length of the discharge, which is usually used to pump repetitive high-pressure multiwavelength radiation sources, is equal to the length of the electrodes of an excimer laser or lamp pumped by a transverse electric discharge. The discharge current-voltage and frequency characteristics, panoramic emission spectra, and the dependences of the relative emission intensity from the halogenides and excited noble gas atoms on the corona discharge current are investigated. The main processes resulting in the production of halogenides, as well as xenon and krypton excited atoms, in the generation regions of a corona discharge are studied.     

YAG:Pr3+的真空紫外光谱分析及其4f5d能级的研究

用共沉淀法制备出不同掺杂浓度的钇铝石榴石(Y3Al5O12,YAG):Pr3+粉末.在不同温度下用同步辐射的真空紫外光(VUV)作为激发光源测量了其发射和激发光谱.对YAG:Pr3+被VUV激发后的发光过程进行了分析,并估算了YAG:Pr3+的声子能量、黄昆因子S及Stokes位移.当用170nm光激发样品时,可能存在自陷激子和通过自陷激子能量传递引发的3P0发射,这种跃迁途径不同于用240nm和289nm两个波长激发后的跃迁途径;对Pr3+在YAG中的4f5d能级进行了研究,从而对其4f5d组态有了一个较清晰的认识.     

Relativistic and correlation effects in the anisotropy of near-threshold Kr 3d and Xe 4d photoionization

Angular distributions of the spin–orbit split components and their branching ratios have been studied experimentally and theoretically for the 3d photoelectrons of Kr and 4d photoelectrons of Xe. The focus was on the electron dynamics near the ionization threshold of each spin–orbit split component and its behaviour as a function of Z   in passing from Kr to Xe. The experimental spectra were measured with high photon and electron energy resolutions with photon energies at about 3–12 eV above the 3d_3/2$3{\text{d}}_{3/2}$ and 3d_5/2$3{\text{d}}_{5/2}$ thresholds for Kr and at about 5–12 eV above the Xe 4d_3/2$4{\text{d}}_{3/2}$ and 4d_5/2$4{\text{d}}_{5/2}$ thresholds. Experimental results for the angular distribution parameters have been compared with theoretical values obtained with relativistic Dirac–Fock method and results from independent particle approximation with a modified Hartree potential [A. Derevianko, W. Johnson, K. Cheng, Atom. Data Nucl. Data Tables 73 (1999) 153]. The branching ratios were compared with theoretical predictions from Dirac–Fock and relativistic random-phase approximation [K. Cheng, W. Johnson, Phys. Rev. A 28 (1983) 2820].     

Vacuum ultraviolet absorption of lithium fluoride crystals grown by zone melting

Optical properties are reported for LiF crystals obtained by zone melting from salts differing in synthesis and purity. The impurity distributions along the bars have been studied by chemical analysis and absorption spectrometry. The transparency is discussed as a function of the number of zone passes.     

Pressure-induced ultraviolet absorption in rare gases: Absorption coefficients for mixtures of Xe and Ar at pressures up to 40 atm in the vicinity of 147 nm

Absorption coefficient κ_υ for mixtures of Xe (0.2–20 kg/cm²) and Ar (5–40 kg/cm²) has been measured in the range 0.1 cm^-1 < κ_υ < 40 cm^-1. Exponential and power dependencies of κ_υ on wavenumber were observed and are discussed. The κ_υ-dependencies on the pressure of mixture components are explained by photon absorption at multiparticle collisions of Xe and Ar atoms.     

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.     

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.