New neutron deficient isotopes with mass numbersA=136 and 145

High resolution laser-atomic-beam spectroscopy was applied to study crossed-second-order effects in the isotope shift of the terms 4f⁷5d6s a¹⁰D and a⁸D for¹⁵¹Eu-¹⁵³Eu. The term dependent effects lead to a difference in the isotope shift of the terms a¹⁰D and a⁸D of 415(20) MHz. The J dependent effects are interpreted through the use of one parameter z_5d for each term; z_5d(a¹⁰D)=41(7)MHz, z_5d(a⁸D)=50(26)MHz.     

Hyperfine structure in the atomic spectrum of niobium

A parametric analysis of the fine and the hyperfine structure for the three even configurations 4d^45s, 4d ⁴5s ² and 4d⁵ has been performed. Effective one-electron parameters a _nl ^kskl(k _s k _l = 01, 12 and 10) and b _nl ⁰² were determined for these three configurations. Extremely large ratios a _4d ¹⁰/a _4d ⁰¹ were found. Theoretical predictions for the hyperfine structure constants A and B for all levels of the configurations 4d^45s, 4d ⁴5s ² and 4d⁵ have been determined from experimental data. Additionally, the fine and hyperfine structure for the two energetically high lying even configurations 4d^46s and 4d^35s6s are discussed. The results presented here call into doubt the existence of the fine structure levels 4d ³5s6s ⁶ F _11/2 at an energy of 39 408.88 cm^-1 and 4d ³5s5p ⁶ G _13/2 at 18 876.46 cm^-1 given in the Moore tables.     

Hyperfine structure and isotope shift of high-lying metastable states of rhenium

Fourteen transitions in ReI, starting from high-lying metastable states belonging to the configurations (5d+6s)⁷, have been studied by laser-induced fluorescence in a collimated atomic beam, and accurate values for the isotope shifts in these transitions as well as for the hyperfine structure constants of 13 metastable and 9 excited states have been obtained. In addition, high precision measurements of the hyperfine structure of the states 5d ⁵ 6s ^{2 4} D _7/2 and 5d ⁶ 6s ⁶ D _{1/2, 3/2, 5/2, 9/2} have been performed using the atomic beam magnetic resonance technique coupled with laser-induced state-selective detection of metastable atoms. The analysis of the hyperfine structure data yields experimental evidence for far configuration mixing effects on the off-diagonal spin-dipole matrix elements. The phenomenological interpretation of the isotope shifts shows the significance of off-diagonal field-shift effects.     

Multimode saturation resonances in optogalvanic spectroscopy: Application to the determination of lande g-factors in zirconium

Resonances corresponding to the matching of laser mode intervals with Lapmor precessional frequencies have been oberved in the discharge current for four transitions in the spectrum of atomic Zr, introduced into a gas discharge by cathodic sputtering. Signals were observed for lower as well as for upper levels. The measured g-factors for the states 4d²5s(a⁴F)5p ³F_2,3,4 and 4d²5s(a²P)5P ³P₂ are symmetrically higher than values given in the literature.     

Determination of hyperfine structures and Rydberg convergence limits of selected optical transitions in 93Nb using resonance ionization spectroscopy

Several two- and three-step schemes for resonance ionization of ⁹³Nb with field ionization of Rydberg levels were investigated in the context of feasibility studies of using ^93m Nb/⁹³Nb isomer ratio determination for fast neutron dosimetry. Hyperfine structures of the states 4d ⁴(a ⁵ D)5p ⁴ D ₁ ^2/0 , 4d ³5_s(a ⁵ P)5P ⁶ D ₁ ^2/0 , 4d ³5s(a ⁵ F)5p ⁶ F ₁ ^2/0 , and 4d ³5s(a ⁵ F)6s ⁶ F _1/2 of ⁹³Nb were measured. The Rydberg spectra of the excitation schemes were measured and corresponding ionization limits estimated.     

Review of Ni-like ion X-ray laser research at Lawrence Livermore National Laboratory

We have demonstrated saturated output on several nickel-like ion X-ray lasers ranging from niobium to silver by using a psec, high-power, chirped-pulse-amplification, tabletop laser. These results have been achieved at wavelengths from 20.3 to 13.9 nm on the Ni-like 3d⁹4d¹S₀→3d⁹4p¹P₁ laser line using a total of 5 to 7 J of energy in a traveling wave excitation scheme. Strong amplification is also observed for Ni-like Sn at 11.9 nm. Gain of 41 cm⁻¹, gain-length product of 18, and output energy of 12 μJ are measured for the Ni-like Pd line at 14.7 nm. For Ni-like Mo, experiments are done using multilayer mirrors to obtain two-dimensional images of the output aperture of the laser and to measure the total laser energy as a function of various parameters such as the delay between the short and long pulses and the energy of the two pulses. For Mo we measure an output energy of 2 μJ and a gain-length product of 16.6. To model the Mo experiments, the LASNEX code is used to calculate the hydrodynamic evolution of the plasma and provide the temperatures and densities to the XRASER code, which then does the kinetics calculations to determine the gain. The temporal and spatial evolution of the plasma is studied both with and without radiation transport included for the 4f and 4p→3d Ni-like Mo resonance lines. High gains are predicted and observed for both the 3d⁹4d¹S₀→3d⁹4p¹P₁ laser line at 18.9 nm and the 3d⁹4f¹P₁→3d⁹4d¹P₁ photopumped line at 22.6 nm.     

Hyperfine-structure investigation in the 6s5d configuration of135Ba and137Ba

The hyperfine structure of the metastable states of the 6s5d configuration of¹³⁵Ba and¹³⁷Ba has been studied by the atomic-beam magnetic resonance (ABMR) method. The metastable barium states were populated in a plasma-discharge inside the atomic-beam oven. The atoms emerging from the ABMR-apparatus were detected by the use of a dyelaser. Compared to conventional methods this technique has the advantage of being state selective. The following magnetic dipole and electric quadrupole interaction constantsa andb have been obtained:¹³⁷Ba:a(³ D ₁)=?520.536 (3) MHzb(³ D ₁)=17.890 (3) MHza(³D₂=415.928 (3) MHzb(³D₂)=25.899 (13) MHza(³D₃)=456.559 (4) MHzb ³D₃=47.390 (16) MHz¹³⁵Ba:a ³ D ₁=?465.166 (4) MHzb(³D₁)=11.642 (4) MHza(³D₂)=371.736(4) MHzb ³ D ₂=16.745 (14) MHza(³D₃)=408.038 (6) MHzb(³D₃)=30.801 (24) MHz Using these constants and the earlier known ones for the¹ D ₂ state the hyperfine structure for the 6s5d configuration has been analyzed with an effective hyperfine hamiltonian. Hyperfine parameters obtained from the analysis have been compared with theoretical values calculated with relativistic self-consistent-field (SCF) wavefunctions. The quadrupole moments have been evaluated with the following result Q(¹³⁵Ba) =0.20(3)b and Q(¹³⁷Ba) = 0.34(4)b uncorrected for the quadrupole shielding.     

Hyperfine structure of the atomic osmium spectrum: Superposition of configurations and the effect of nucleus volume

The contributions of the superposition of configurations ns ²5d ⁷6s+ns5d ⁷6sn′s+ns5d ⁷6s ² (n=1–5, n′=7–10) to the parameters of the hyperfine structure a _5d ⁰¹ , a _5d ¹² , a _5d ¹⁰ , a _6s ¹⁰ in the spectrum of the osmium atom Os I are calculated. Nonzero contributions are shown to be made only to the parameters a _5d ¹⁰ and a _6s ¹⁰ . This fact justifies the inclusion of the parameter a _5d ¹⁰ in the semiempirical analysis of experimental values of magnetic dipole constants of the hyperfine structure of the 5d ⁷ s configuration in the spectrum of the osmium atom. The effect of nucleus volume on the parameters of the hyperfine structure in the spectra of osmium isotopes ¹⁸⁷Os and ¹⁸⁹Os is estimated.     

Hyperfine anomaly in the spectrum of the osmium atom. effect of the spatial distribution of nuclear charge

Contributions of the superposition of configurations ns ²5d ⁸+ns5d ⁸ n′s (n=1–5, n′=6–10) and ns ²5d ⁶+ns5d ⁶ n′s (n=1–6, n′=7–10) to parameters a _5d ⁰¹ , a _5d ¹² , and a _5d ¹⁰ of the hyperfine structure in the spectrum of the osmium atom OsI are calculated. It is shown that the nonzero contribution is made only to a _5d ¹⁰ . The effect of the spatial distribution of nuclear charge on the parameters of the hyperfine structure in the spectra of ¹⁸⁷Os and ¹⁸⁹Os isotopes and on the hyperfine anomaly for the 5d ⁷6s levels in the spectrum of these isotopes is estimated.     

X-Ray photoelectron and mössbauer spectroscopy studies on molybdenum-bearing ferrite

The X-ray photoelectron spectra of Mo 3d electrons (232.4–232.9 and 229.4–229.6 eV) for Mo-bearing ferrites have suggested that molybdenum ions are in the 4+ valence state on the lattice points in the spinel structure. The XPS data for Mo 3d and Fe 2p electrons combined with the Mössbauer data at room temperature suggest that Fe₂MoO₄ takes a valence state (Fe²⁺)_tet[Fe²⁺Mo⁴⁺]_octO₄.     

Hyperfine and Zeeman studies of low-lying atomic levels of181Ta and the nuclear electric quadrupole moment

The hyperfine structure of the atomic levels 5d ³ 6s ^{2 4} F _{7/2, 9/2} and⁴ P _1/2 in¹⁸¹Ta has been studied by atomic-beam magnetic-resonance. Using intermediate coupling wave functions derived for the configurations (5d+6s)⁵ the hyperfine structure data of six low-lying metastable states have been analyzed with respect to the effective operator formalism. The effective radial parameters for the magnetic dipole and electric quadrupole interactions are determined from these measurements and compared with relativistic calculations. The value obtained for the spectroscopic quadrupole moment of the¹⁸¹Ta nuclear ground state is Q_hfs=3.44(17) barn (uncorrected for configuration interaction effects).     

Use of sturmian expansions in calculations of the hyperfine structure of atomic spectra

A procedure for calculating hyperfine structure (HFS) parameters using the basis of Sturmian functions is developed. The procedure is used to calculate the HFS parameter a _4d ⁵ of the 4d ⁵ levels of the niobium atom. The contributions of the continuous spectrum and higher orders of the perturbation theory are quantitatively estimated by comparing the numerical values of the parameter a _4d ¹⁰ obtained in the framework of the perturbation theory with the results of direct calculations by the configuration interaction method. Comparison of the results of relativistic and nonrelativistic calculations allows the contribution of relativistic effects to HFS parameters to be found.     

Monitoring of the lifetimes of the metastable states in Au in an air-acetylene flame as a probe for local stoichiometric conditions by the laser-enhanced ionization technique

The behaviour of the lifetimes of the metastable 5d ⁹ 6s ^{2 2} D _3/2 and 5d ⁹ 6s ^{2 2} D _5/2 states in Au in an air/acetylene flame has been studied using the step-wise delayed laser-enhanced ionization technique. Using a new, fast and reliable, automated experimental procedure, we have conducted a systematic investigation of the lifetimes for various flame characteristics, namely lateral and vertical position in the flame and flame composition. It was found that the lifetimes of the metastable states are affected by at least three different mechanisms: i) a rather small but almost constant quenching rate, unaffected by the variations in the flame environment; ii) quenching by oxygen, which is proportional to the local partial pressure of oxygen; and iii) quenching by unburned fuel components. We have shown that by monitoring the lifetime of a metastable state as a function of various flame parameters, the conditions for local stoichiometry in the flame can be determined by this technique.     

紫外激光离解四氯化钛产生的钛原子的受激喇曼散射

紫外激光(259—300nm)离解四氯化钛产生了大量钛原子,它们主要处于钛原子的基态a³F₂和亚稳态a³F_3,4上。通过近共振跃迁对处于a³F_2,3,4态上的钛原子进行泵浦,观测到一系列钛原子的受激喇曼散射和受激辐射,并对所有谱线进行了认证。钛原子的受激喇曼散射的脉宽和时间分辨谱表明,紫外激光离解四氯化钛产生钛原子的过程非常迅速,估计所需时间≤1ns。 关键词：     

Investigation of the hyperfine structure of electronic levels in chromium atom

Measurements of the hyperfine structure (hfs) of electronic levels of the chromium atom were performed using two spectroscopic methods. For 7 energy levels (3 even parity and 4 odd parity) the magnetic dipole and electric quadrupole hyperfine interaction constants A and B were determined for the first time. In this case the method of laser induced fluorescence (LIF) on an atomic beam was used. The low lying metastable levels belonging to the term 3d⁴4s² a⁵D were remeasured by the method of laser-rf double resonance on an atomic beam (ABMR-LIRF). To improve the accuracy of hyperfine splittings measurements, the stability of the radio frequnecy (rf) generator was increased by the use of a frequency standard synchronized by a GPS signal. The values of the hfs intervals for these levels were determined with the accuracy of a few kHz. The improvement in accuracy enabled an estimation of the octupole-coupling constant C.     

Analysis of the lattice,strong coupling series for g0φ4 field theory in d dimensions

We analyze the renormalized strong coupling series for lattice g₀φ⁴ field theory which is a double series in x = M⁴a⁴/g₀a_4?dandy = 1/M²a², where M is the renormalized mass, a the lattice spacing, g₀ the bare coupling constant and d the dimension of space-time. We extrapolate to large y for fixed x by using a Padé-like extrapolation technique. We study the dimensionless renormalized coupling constant G/M^4?d and find that as we approach the continuum(x → 0, y → ∞) the entire spectrum of g₀ from zero to infinity can be studied. Our results for d = 1,2,3,4 based on a series in y up to y⁵ and in x up to x³ show that for fixed lattice spacing a, G/M^4?d is a monotonic function of g₀ ranging from zero at g₀ = 0 to a maximum at g₀ = ∞. Using the high temperature expansion results, we have also derived 9 terms in y on 8 lattices of dimension 1,2,3 and 4 for the linear term in x, and studied this series to see if one can see a breakdown in this monotonic behavior of G for large y. The analysis of this latter series is inconclusive.     

Experimental evidence for far configuration mixing effects on off-diagonal hfs interaction between the (3d+4s) N+2 configurations of free atoms

In our systematic investigations on the hyperfine structure (hfs) of high lying metastable states in 3d-shell atoms we have found evidence for an extraordinary strong far configuration mixing effect on off-diagonal matrix elements between configurations. Using theABMR-LIRF method the hfs of (3d ² 4s ²)³ P ⁴⁷Ti, (3d ³ 4s ²)⁴ P ⁵¹V (3d ⁵ 4s ²)⁴ G ⁵⁵Mn and (3d ⁶ 4s ²)³ H ⁵⁷Fe has been measured. Values found for the effective radial parameters \(a^{k_s k_l } \) of the magnetic dipole interaction disagreed up to 300% with those known from hfs measurements of lower lying multiplets of the same configuration, even when intermediate coupling and electrostatically correlated second order hfs effects within each of the configurations are taken into account. We suggest that the main part of these discrepancies can be explained, if two-body core polarization is considered, which screens the ordinary one-body core polarization parametera _3d ¹⁰ . Preliminary values for the corresponding parameters are given.     

The lowest triplet state of luminescent scheelites: a study of the MoO24- ion by electron paramagnetic resonance with optical detection

The fine-structure and g tensors of the luminescent triplet state of the molybdate anion in single-crystals of CaWO₄:MoO₄, CdMoO₄ and PbMoO₄, all with the scheelite structure, are reported. In all three hosts the MoO24- ion is distorted on excitation. The directions of the principal axes of the fine-structure and g tensors support the idea that the effect results from the combined action of a Jahn-Teller instability and the crystal field. The hyperfine coupling of the ⁹⁵Mo and ⁹⁷Mo nuclei points towards excitation to an orbital with a large contribution of Mo 4d_3z2-2r.     

The Fokker-Planck equation for quantum noise of theN-level system

The hyperfine structure of the ReI-lines λκ 4889 å (5d⁵ 6s 6pz ⁸P_7/2?5d⁵ 6s² a ⁶S_5/2) and 5275 å (5d⁵ 6s 6p z⁸P_5/2?5d⁵ 6s² a⁶S_5/2) was measured by a photoelectric recording double Fabry Perot spectrometer using enriched isotopes of Re¹⁸⁵ and Re¹⁸⁷, which have been excited in liquid air cooled hollow cathodes. Besides the usual recording the signal was also measured by a digital voltmeter and punched into paper tape making it possible to evaluate the measurements by a computer. The linewidth obtained in the experiments was small enough that besides the splitting of the⁸P states also the splitting of the ground state could be detected in asymmetries of the hyperfine structure components. By the mathematical analysis of the components it was possible to derive the quadrupole coupling constantB of the 5d⁵ 6s² a ⁶S_5/2 ground state: 5=1.6(8)· 10^?3cm^?1 for Re¹⁸⁵ and Re¹⁸⁷. The quadrupole moments of Re¹⁸⁵ and Re¹⁸⁷ have been estimated fromB (z⁸P_{7/2, 5/2}) with LS coupling eigenfunctions considering relativistic effects: Q(Re¹⁸⁵)=2.30 (4) [90] · 10^?24 cm² Q (Re¹⁸⁷)=2.20 (4) [90] · 10^?24 cm². (Figures in round brackets are experimental errors, those in square brackets are estimated uncertainties introduced by the theoretical evaluation.) Using these results and the knownB (a ⁶S_5/2) of Re¹⁸⁶ and Re¹⁸⁸ also the nuclear quadrupole moments of these isotopes were derived. Q(Re¹⁸⁶)≈Q(Re¹⁸⁸)≈0.4 · 10^?24 cm².     

Electronic structure and magnetism in 4d-transition metal clusters

We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (O_h) and icosahedral (I_h) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of O_h and I_h clusters as a function of the atomic number along the 4 d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations. Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998