Multiwave excimer lamps using XeF/XeCl/KrF/KrCl molecules

Results are presented of an investigation of the spectral and temporal characteristics of an electricdischarge excimer lamp emitting simultaneously on the 351 nm XeF, 308 nm XeCl, 249 nm KrF, and 222 nm KrCl transitions. The He/Kr/Xe/SF₆/HCl working mixtures were excited in a transverse discharge with ultraviolet spark preionization at a total pressure of 25–100 kPa. In order to obtain the same brightness the concentration ratio [Kr]/[Xe] for the excimer molecular transitions was 8/0.8 kPa, and that for the halogen-containing molecules was [SF₆]/[HCl][=[0.06–0.12]/[0.08–0.16] kPa. The duration of the radiation pulses for the excimer molecular transitions at atmospheric pressure was 100–200 ns and when the total mixture pressure was reduced to 250 kPa, this was doubled or trebled. The service life of the spontaneous radiation for B-X transitions in excimer molecules was 10⁵ pulses. Zh. Tekh. Fiz. 68, 64–67 (December 1998)     

Experimental and theoretical study of the far-infrared spectra of HCl dissolved in liquid Ar,Kr, and Xe

New experimental results are reported on the relative absorption intensity distribution in the FIR spectra of HCl dissolved in liquefied Ar, Kr, and Xe at several temperatures along the liquid—vapour coexistence curve. These are treated further by applying a previously developed quantum-statistical spectral theory, which accounts for the line mixing and memory effects. Theoretical spectra are given in terms of the anisotropic potential time autocorrelation functions obtained from classical MD simulations using several empirical analytical potentials with density-adjusted well depths. Globally fair agreement between the theoretical and experimental spectra is demonstrated, except in the high frequency wings, where the theory underestimates the observed intensities. The choice of a particular radial form for the anisotropic HCl/RG potentials is found to be not critical for reproducing the experimental absorption profiles.     

Infrared diode laser spectroscopy of the Kr–N2O van der Waals complex: the v 1 symmetric stretch region of N2O

The rovibrational spectra of four isotopomers of the Kr–N₂O van der Waals complex, namely ⁸²Kr–N₂O, ⁸³Kr–N₂O, ⁸⁴Kr–N₂O and ⁸⁶Kr–N₂O, were measured in the v ₁ vibrational band region of the N₂O monomer (～1285?cm^?1) using a tunable diode laser spectrometer to probe a pulsed supersonic slit jet. Rotational constants for both ground and excited vibrational states of these four isotopomers were accurately determined. The band-origin of Kr–N₂O was observed to shift by +0.1065?cm^?1 from that of the monomer. The band-origin shifts of Rg–N₂O (Rg?=?Ne, Ar, Kr) in the v ₁ vibrational band region could also be well explained by the model based on a Buckingham intermolecular potential [W.A. Herrebout, H.-B. Qian, H. Yamaguchi and B.J. Howard, J. Mol. Spectrosc. 189, 235 (1998)]. But the band-origin shift of He–N₂O was found to deviate significantly from this model. The possible reason is discussed and the band-origin shift of Xe–N₂O predicted.     

Electrical and optical characteristics of inert-gas plasmas in spatially nonuniform electrode systems

The characteristics of unipolar and bipolar corona discharges in mixtures He/Ar/Kr, He/Ar/Xe, and He/Kr/Xe at atmosphere pressures in electrode systems of the point-plane and point-grid type distributed along the length. It is shown that bipolar corona discharges can be used in the preionization systems of high-pressure inert-gas-atom lasers. The spectral characteristics of the plasma are investigated, and the dependence of the relative intensity of the radiation in the lines Ar(4s-4p), Kr(5s-5p), and Xe(6s-6p) on the composition and pressure of the working mixtures and on the value of the corona discharge current are determined. Zh. Tekh. Fiz. 67, 15–18 (November 1997)     

Measurement of the rate of nuclear capture of negative muons in the isotopes 84Kr and 136Xe

The lifetime of a negative muon in the 1S state in the isotopes ⁸⁴Kr and ¹³⁶Xe was measured. The values obtained, τ(⁸⁴Kr)=139.2±2.9 ns and τ(¹³⁶Xe)=111.0±4.6 ns, correspond to total nuclear capture rates Λ_c(⁸⁴Kr)=6.75±0.15 μs⁻¹ and Λ _c(¹³⁶Xe)=8.6±0.4 μs⁻¹. Theoretical calculations of the rate of nuclear capture of a negative muon are performed for the Kr isotopes. The experimental results are compared with the theoretical calculations. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 5, 302–307 (10 March 1998)     

Infrared spectra of the Kr—CO and Xe—CO van der Waals complexes

The infrared spectra of the weakly bound complexes Kr—CO and Xe—CO have been studied in the region of the CO stretching vibration (4.7 μm) using a high-resolution tuneable diode laser probe. The complexes were observed in a long path (200 m) low temperature (76 K) gas cell (Kr—CO) and in a pulsed supersonic jet expansion (Kr—CO and Xe—CO). Previous long path cell measurements on these complexes at lower resolution analysed only the K = 0 and 1 stacks of rotational levels in the ground intermolecular vibrational state. The new data extend up to K = 3 (Xe—CO) or 4 (Kr—CO), and also include K = 0 and 1 stacks in the excited bending state, ν₂ = 1. The bending frequencies for Kr—CO and Xe—CO (in the ν_co = 1 upper state) were determined to be 13.156cm_?1 and 13.794cm^?1, respectively. Detailed molecular parameters were determined to describe the rotational energy levels of each complex using a simple empirical Hamiltonian. These results enable parameters to be compared for the entire series of rare gas—carbon monoxide complexes, from He—CO to Xe—CO. Also they will guide the future development and evaluation of accurate intermolecular potential energy surfaces for Kr—CO and Xe—CO.     

Independent yields of Kr and Xe isotopes in the photofission of heavy nuclei

The yields of Kr (A = 87–93) and Xe (A = 138–143) primary fission fragments produced in ²³²Th, ²³⁸U, and ²⁴⁴Pu photofission upon the scission of a target nucleus and neutron emission were measured in an experiment with bremsstrahlung from electrons accelerated to 25 MeV by a microtron, and the results of these measurements are presented. The experimental procedure used involved the transportation of fragments that escaped from the target by a gas flow through a capillary and the condensation of Kr and Xe inert gases in a cryostat at liquid-nitrogen temperature. The fragments of all other elements were retained with a filter at the capillary inlet. The isotopes of Kr and Xe were identified by the γ spectra of their daughter products. The mass-number distributions of the independent yields of Kr and Xe isotopes are obtained and compared with similar data on fission induced by thermal and fast neutrons; the shifts of the fragment charges with respect to the undistorted charge distribution are determined. Prospects for using photofission fragments in studying the structure of highly neutron-rich nuclei are discussed.     

Lineshapes of the even mp1/2 5n(p′/f′) autoionizing resonances of Ar, Kr and Xe

The even parity mp_1/2 ⁵np^′ and mp_1/2 ⁵nf^′ autoionizing resonances of Ar, Kr, and Xe (m=3,4,5) were investigated experimentally and theoretically by one-photon excitation from lower-lying intermediate levels. In particular, high resolution measurements for the Ar(nf^′), Kr(12p^′,8f^′), and Xe(8p^′) resonances are reported; lineshape parameters for these resonances have been derived by a Fano-type analysis, thus yielding reduced resonance widths. The experimental spectra and the resonance parameters are compared with theoretical calculations which are based on the configuration interaction Pauli–Fock approach including core polarization. The measured and calculated lineshapes are in good agreement. In addition, theoretical predictions are presented for other resonances, which have not yet been observed experimentally, and some systematic trends are elucidated.     

Electronic and geometric structure of doped rare-gas clusters: surface, site and size effects studied with luminescence spectroscopy

The electronic and geometric structure of rare gas clusters doped with rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation spectroscopy in the VUV spectral range. Several absorption bands are observed in the region of the first electronic excitations of the impurity atoms, which are related to the lowest spin-orbit split atomic ³P₁ and ¹P₁ states. Due to influence of surrounding atoms of the cluster, the atomic lines are shifted to the blue and broadened (“electronical cage effect”). From the known interaction potentials and the measured spectral shifts the coordination of the impurity atom in Ar_N, Kr_N, Ne_N and He_N could be studied in great detail. In the interior of Kr_N and Ar_N the Xe atoms are located in substitutional sites with 12 nearest neighbours and internuclear distances comparable to that of the host matrix. In Ne_N and He_N the cluster atoms (18 and 22, respectively) arrange themselves around the Xe impurity with a bondlength comparable to that of the heteronuclear dimer. The results confirm that He clusters are liquid while Ne clusters are solid for N≥ 300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is strong, small Rg_m-clusters (Rg = Xe, Kr, Ar, m≤10 ²) are formed in the interior sites of the host cluster made of Ne or He. Specific electronically excited states, assigned to interface excitons are observed. Their absorption bands appear and shift towards lower energy when the cluster size m increases, according to the Frenkel exciton model. The characteristic bulk excitons appear in the spectra, only when the cluster radius exceeds the penetration depth of the interface exciton, which can be considerably larger than that in free Rg_m clusters. This effect is sensitive to electron affinities of the guest and the host cluster.     

Accurate ground-state potential energy surfaces of the C2H2–Kr and C2H2–Xe van der Waals complexes

Accurate ab initio intermolecular potential energy surfaces (IPES) have been obtained for the first time for the ground electronic state of the C₂H₂–Kr and C₂H₂–Xe van der Waals complexes. Extensive tests, including complete basis set and all-electron scalar relativistic results, support their calculation at the CCSD(T) level of theory, using small-core relativistic pseudopotentials for the rare-gas atoms and aug-cc-pVQZ basis sets extended with a set of 3s3p2d1f1g mid-bond functions. All results are corrected for the basis set superposition error. The importance of the scalar relativistic and rare-gas outer-core (n–1)d correlation effects is investigated. The calculated IPES, adjusted to analytical functions, are characterized by global minima corresponding to skew T-shaped geometries, in which the Jacobi vector positioning the rare-gas atom with respect to the center of mass of the C₂H₂ moiety corresponds to distances of 4.064 and 4.229?Å, and angles of 65.22° and 68.67° for C₂H₂–Kr and C₂H₂–Xe, respectively. The interaction energy of both complexes is estimated to be ?151.88 (1.817?kJ?mol^?1) and ?182.76?cm^?1 (2.186?kJ?mol^?1), respectively. The evolution of the topology of the IPES as a function of the rare-gas atom, from He to Xe, is also discussed.     

The fundamental vibrational shift of HCl diluted in dense Ar and Kr

The fundamental infrared band vibrational shifts of HCl diluted in dense Ar and Kr have been calculated by means of molecular dynamics simulation techniques and compared with the experimental data reported by Pérez et al. (J. Chem. Phys. 122, 194507 (2005)). The results have been analysed along the liquid–vapour coexistence line as in several supercritical states, with good agreement between the theoretical and experimental values.     

Energy loss spectra of xenon and krypton and their analysis by energy-dependent multichannel quantum defect theory

Oscillator strengths of xenon and krypton for transitions from the ground state to the optically allowed states forming the five resonance series were measured by means of high energy electron spectroscopy (HEEIS). The rather irregular behaviour of these oscillator strengths is analyzed with the aid of the known atomic level energies by means of the energy-dependent quantum defect theory. With the parameters obtained by the analysis of the energy loss measurement autoionized lines shapes and the asymmetry parameter for the photoionizationβ of Kr and Xe were calculated in excellent agreement with experimental data from the literature. The comparison of the parameters and their energy dependence for Kr and Xe gives indication that some properties change rather rapidly from Kr to Xe. The theory enables also to predict missing term levels of Kr.     

Microscopic study of yrast bands and backbending anomaly in 78-82Kr isotopes

The yrast spectra of ^78-82Kr are studied by using the projected shell model (PSM) approach. The energy states are obtained by taking oblate as well as prolate quadrupole deformations for ^78-82Kr. The structure of yrast states and backbending phenomena are investigated. The theoretical results predict low-lying states in ^{78, 82}Kr to be oblate and coexistence of oblate-prolate shapes for ⁸⁰Kr. The B(E2) transition probabilities and g-factors are obtained and compared with the available experimental data.     

Die Anregung des Tochterions Rb+ durch die plötzliche Kernladungsänderung von85Kr,eingebaut in feste Edelgase

By the sudden change of nuclear charge the daughter-ion is excited with a propability of some percent (monopole-excitation). When⁸⁵Kr is trapped in various solids of rare gases, the daughter-ion Rb⁺ acts as a probe: The spectra of emitted photons contain information about the influence of the surrounding solid on the levels of the excited Rb⁺. These spectra have been observed in delayed coincidence with the nuclear process (β-decay); direct excitation by charged particles is excluded. The results are closely connected to the behaviour of the decaying atom in free state and solid krypton: There are narrow bands (the daughter-ion occupies a regular lattice site) and blue-shifted (Δ v) broad bands (emission from daughter-ion displaced to interstitial sites by recoil).Δ v is different in the various solids of rare gases and increases from Ar to Xe; this is due to the various polarizabilities and lattice constants. A theoretical estimate fits well the experimental values. Besides, the experimental results show that the excitation-probability for⁸⁵Kr in Kr is greater than for⁸⁵Kr in Ar or Xe, which also agrees with theoretical estimates. Furthermore, information about the displacement energies of the Rb⁺ in the various solids of rare gases are gained from the ratio of intensities of the narrow bands to that of the broad bands, which are compared to displacement energies gained from rare-gas pair potentials.     

A model for viscosity coefficients of gases with potentials differing in form

A recent theory of non-conformal interactions has been very succesful in providing effective spherical potentials for the pressure of more than 40 real gases and many of their binary mixtures. Here, this theory is applied to deal with low-density viscosity coefficients. In its simplest form, the approximate non-conformal (ANC) theory introduces, besides the usual corresponding states parameters-energy ? and distance r_m-a softness parameter s to account for the form of a particular potential function. We investigate the effects of the potential form on the temperature behaviour of the viscosisty coefficient η. It is shown that the softer potentials, with wider attractive wells, have larger viscosities and an explicit expression for η (T, ?, r_m, s) is obtained. The ANC potentials are tested in their capacity to reproduce the temperature dependence of η for the heavier noble gases (Ar, Kr and Xe), diatomics (H₂, N₂, O₂ and CI₂) and a dozen small polyatomics. It is found that the ANC model η (T, ?, r_m, s), with only three substance-dependent parameters, reproduces experimental 7 data within their estimated error.     

Vibrational moments of fundamental transitions in low-temperature molecular liquids: Determination from the band shape of vibrations in the overtone spectral range

It is shown that the integrated absorption coefficients of strong fundamental bands of some gaseous substances can be determined with an accuracy of 5–10% using experimental data on the spectral moments of bands in the overtone spectral range of these substances in the liquid phase near the melting point. The absorption coefficients are calculated within the framework of the cell model of the liquid state from the contributions of the resonance dipole-dipole interaction to the second spectral moment. The combination and overtone absorption bands of the SF₆, CF₄, SiF₄, NF₃, CHF₃, CC1F₃, CBrF₃, OCS, N₂O, and CO₂ molecules in the liquid state and in solutions in liquefied Xe, Kr, and O₂ are recorded. The data in the literature on the intensity of strong IR bands in the gas phase are analyzed. Using an improved experimental technique, additional measurements are performed. It is found that the absorption coefficients determined from the spectral characteristics of the liquids agree well with the coefficients measured in the gas phase.     

Identification of structures in absorption spectrum of Kr-Xe gas mixtures close to the Xe resonance line at 146.96 nm

The origins of spectral structures that appear close to the Xe resonance line at 146.96 nm in absorption spectra of Kr gas with an admixture of Xe are discussed in this paper. It is shown that these structures can result from bound-bound and bound-free transitions in the Xe-Kr molecule between the ground state and the 1(³P₁) excited state, which both are weakly-bound. The depth of the excited state is estimated. An introduction of a hump on the 1(³P₁) state internuclear potential is suggested. Received 15 December 1999 and Received in final form 20 February 2000     

Isomers of astrophysical interest in neutron-deficient nuclei at masses A = 81, 85 and 86

Decay properties of neutron-deficient exotic nuclei close to A=80 have been investigated at the IGISOL facility. The studied nuclei, ⁸¹Y, ⁸¹Sr, ^81mKr, ⁸⁵Nb, ⁸⁵Zr, ⁸⁶Mo and ⁸⁶Nb, were produced by a ³²S beam from the Jyv?skyl? isochronous cyclotron on ⁵⁴Fe and ^natNi targets. The internal conversion coefficient for a 190.5 keV isomeric transition in ^81mKr has been measured and the internal transition rate has been determined. The internal transition rate has been used to estimate a neutrino capture rate on ⁸¹Br, which yields a log ft of 5.13±0.09 for the reaction ⁸¹Br( ν, e ^-)^81mKr. A new isomer with a half-life of 3.3±0.9 s has been observed in ⁸⁵Nb. The existence of an earlier reported isomer with a half-life of 56 s in ⁸⁶Nb has not been confirmed.     

The scattering of He from adsorbed layers of gases on Ag(110)

The adsorption of gases on Ag(110) has been studied using inelastic He atom scattering. Vibrational spectra have been obtained for Kr, Xe, C₂H₆, C₂H₄, CH₄, CF₄, CHF₃, CO₂ and H₂O. Spectra have also been obtained for multilayers of Xe (2 layers) and C₂H₆ (3 and 4 layers) where the energy changes move to lower values. The scattering from Kr and Xe can be shown to be dispersionless as has been previously found for these adsorbates on Cu(100) and Cu(110). The energy changes for Kr and Xe are smaller than on Cu surfaces and attempts were made to account for this based on an Einstein model of the adsorbed atoms in the surface holding potential.     

Independent electron theory of multiple ionization of xenon by intense laser pulses

The intensity dependence of the multiphoton ionization spectra of Xe atoms has been investigated with an improved accuracy and well-controlled laser parameters. In particular, we have examined the ionization rates for X³⁺, X²⁻, X⁺ as functions of the laser intensity and the pressure in the target chamber. The apparatus used for these measurements is characterized by a high-energy resolution (better than 200 meV) and a completely digital acquisition system. The time-of-flight spectra clearly show the contributions of the different isotopes present in Xe gas. The laser pulses have been characterized with great accuracy by monitoring the energy, pulse width and divergence shot by shot. The ionization rates of the different ions have been used for testing the basic assumption of the Geltman theory of multiple ionization based on the single electron ionization model. We have found that for the small intensity range investigated the quantity (dXe ⁺/dI)·(dXe ³⁺/dI)/(dXe ²⁺/dI)² appears to be quite close to the value 0.5 predicted by this model.