Experimental study of autoionizing states of AuI

This paper describes the investigation of the autoionizing states of AuI by exciting the states of 6d ² D _3/2 and 6d D _5/2 with tunable dye lasers by means of a resonance ionization time-of-flight mass spectrometer (RI-TOFMS). Many new autoionizing states were found, a few of which have narrow-linewidths of about 0.1 cm^–1. The photoionization efficiencies for different channels were compared. Among the autoionizing states found so far, the highest photoionization yield is given by two newly obtained states from the state 6d ² D _5/2, 3683.6 cm^–1 and 4636.5 cm^–1 above the first ionization limit. In addition, the Shore-Fano profile parameters of several autoionizing resonances were determined by a nonlinear fitting program.     

The fine structure levels and spin-singlet contributions to zero-field-splitting parameters of Cr2+ ion in CdGa2S4

A theoretical investigation is reported of the fine structure levels and the spin-singlet contributions to zero-field-splitting (ZFS) parameters for Cr²⁺ ion in CdGa₂S₄ crystals. Firstly, the complete energy matrix including all spin states for a 3d ⁴ ion in tetrahedral D _2d symmetry is constructed according the double-group chain in the strong-field scheme. Then, by diagonalizing the complete energy of electron–electron interactions, the crystal field and the spin–orbit coupling for the Cr²⁺ (3d ⁴) ion in CdGa₂S₄ crystal, the fine structure levels and the spin-singlet contributions to ZFS parameters a, D and F are calculated. The results show that the spin-singlet contribution to D is negligible, but the contributions to a and F are very important. So, to obtain more accurate ZFS parameters for 3d ⁴ ions in the tetrahedral crystals, all spin states should be considered.     

Ba原子6pnd(J=1, 3)自电离光谱的实验研究

采用三台可调谐激光实施孤立实激发,分三步将处于基态的Ba原子激发到6p_1/2nd(J=1,3)和6p_3/2nd(J=1,3)自电离态上,获得了分别从6snd¹D₂(n=7—15)和6snd³D₂(n=7—12) 激发而得到的6p_1/2nd(J=1,3)和6p_3/2nd (J=1,3)自电离光谱,重点对主量子数n较低的自电离态进行了实验研究. 通过光谱的线形拟合得到了上述能级的位置和宽度等数据,进而获得了量子亏损和约化宽度等信息. 通过对不同系列的自电离光谱的分析和比较,详细讨论了这些自电离态的光谱特征及其复杂光谱结构的成因. 关键词： 孤立实激发 组态相互作用 自电离态     

Surface dipole barrier in metals. Relation to the bulk electron density

The surface dipole barrierD of transition and non transition metals is calculated from experimental policrystalline work functions and theoretical chemical potentials obtained by the Augmented Spherical Waves Method. An universal linear relation is discovered betweenD andn _b ^non-d , the non-d part of the electron density at the boundary of bulk atomic cells. This suggests that the surface dipole barrier is mostly due to the non-d electrons.     

Computational study of collisional energy transfer and quasi-continuous population inversions in laser-pumped Ca vapor

A computational study of population inversion between several pairs of excited states viz 3d4p ³ F-4s3d ³ D, 4s5s ³ S-4s4p ³ P and 4s3d ³ D-4s4p ³ P in Ca vapor pumped on the 4s ^{2 1} S ₀-4s4p ³ P ₁ transition is presented. The main aim is to investigate the influence of various atomic processes in creating and sustaining the population inversion for long times after the excitation pulse. The delicate interplay between superelastic energy transfer to free electrons, energy pooling collisions and cascaded recombination is particulary examined. It is noted that quasi-continuous population inversion can be readily excited on the 4s3d ³ D-4s4p ³ P transitions; and under some conditions, also on the 4s5s ³ S-4s4p ³ P transitions. Furthermore, inversion on the 3d4p ³ F-4s3d ³ D transitions can also be excited for a considerable length of time. The results may be useful in designing and developing quasi-cw metal vapor lasers.     

Radiative lifetimes of 7d, 8d <Superscript>1</Superscript>D<Subscript>2</Subscript> excited states of Hg I

Radiative lifetimes of 7d, 8d ¹ D ₂ excited states of Hg I are measured using pulsed two-photon excitation from the ground [Xe]5d ¹⁰6s ^{2 1} S ₀ mercury state, detecting the decay of the laser-induced fluorescence. The results are compared with theoretical values, obtained by means of a Hartree-Fock single configuration method, taking into account electron configuration interaction. The radiative lifetime value dependence on the effective principal quantum number for the nd ¹ D ₂ series is analyzed and compared with the quantum defect dependence. Received 25 February 2000 and Received in final form 26 July 2000     

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.     

Nuclear charge radii and electromagnetic moments of scandium isotopes and isomers in the f7/2 shell

Collinear laser spectroscopy experiments on the ScII transition 3d4s ³D₂→3d4p ³F₃ at λ ≈ 363.1 nm were performed on the ^42–46Sc isotopic chain using an ion guide isotope separator with a cooler–buncher. Isotope and isomer shifts and hyperfine structures of five ground states and two isomers were measured. Preliminary results on the nuclear moments and charge radii changes deduced from these measurements are reported.     

Stark effect,hyperfine structure and isotope shifts in highly excited states of BaI and CaI

The electric dipole polarizabilities of 9 even-parity barium states (6s8s ¹ S ₀,³ S ₁; 6s7d ¹ D ₂,³ D _1,2; 5d7s ¹ D ₂ and 6p ^{2 3} P _0,1,2) in the interval 33,800–35,800 cm^?1 have been measured with high resolution laser-atomic-beam spectroscopy. Simultaneously, values of isotope shifts and hyperfine coupling constants for theJ=1 states have been obtained. Comparison of the experimental polarizabilities with calculated values as well as inspection of the data on isotope shifts and hyperfine structure from the present and earlier work strongly suggests erroneous assignments of theJ=2 states, with an exception for the 5d 7s ¹ D ₂ state. The influence of an electric field on the 3d ^{2 3} P _0,1,2 states of calcium has also been studied. A marked departure from a quadratic Stark effect has been observed at relatively small field strengths. This can be attributed to the large polarizabilities of neighbouring Rydberg states. The low field data allow the determination of admixtures of Rydberg states into the 3d ^{2 3} P-states as small as 0.02%.     

Emission of cadmium excited ions upon α particle bombardment

Ion emission due to the sputtering of metallic cadmium by α particles from ²³⁸Pu is studied. Experiments are carried out in helium at different cadmium foil temperatures (from 20 to 280°C) and gas pressures (from 75 to 2200 torr). The sputtering of the metallic cadmium causes the emission of Cd(II) excited ions in the 4d ⁹5s ²² D _{3/2, 5/2} and 4d ¹⁰6s ² S _1/2 states. Above 160°C, the population of these stares grows exponentially. At a temperature of 240°C and a helium pressure in the chamber of 600 torr, the sputtering ratio of metallic cadmium is found to be 6.26×10⁻¹⁴ g per α particle; i.e., one α particle knocks out about 10⁸ cadmium atoms from the foil. From spectroscopy and microphotography examinations of the metallic sample surface, a two-step model of ion emission is suggested. The model involves (1) the formation of a high-temperature wedge, which ejects a cadmium droplet, and (2) self-diffusion of displaced cadmium atoms in the droplet toward the surface.     

Effect of crystal field on the spin density at the copper nucleus in copper complexes

The role of lower symmetry component of the crystal field in causing a mixing of excited 3d ^x−1 4s with the ground 3d ^x configuration and leading to spin density at the nucleus for iron group ions was suggested by Griffith and Orgel. This mechanism has been examined in detail for the two low-symmetry copper complexes, one square planar (D_4h symmetry) and the other distorted tetrahedron (D_2d symmetry) and the calculation has been performed using the powerful Racah method and tensor operator technique. It is found that for the two types of copper complexes, copper pthalocyanin (square planar, D_4h symmetry) and cesium copper chloride (distorted tetrahedron, D_2d symmetry) the contribution from this mechanism to the spin density at the nucleus vanishes identically.     

Flame front tracking in turbulent lean premixed flames using?stereo PIV and time-sequenced planar LIF of OH

This paper describes the simultaneous application of time-sequenced laser-induced fluorescence imaging of OH radicals and stereoscopic particle image velocimetry for measurements of the flame front dynamics in lean and premixed LP turbulent flames. The studied flames could be acoustically driven, to simulate phenomena important in LP combustion technologies. In combination with novel image post processing techniques we show how the data obtained can be used to track the flame front contour in a plane defined by the illuminating laser sheets. We consider effects of chemistry and convective fluid motion on the dynamics of the observed displacements and analyse the influence of turbulence and acoustic forcing on the observed contour velocity, a quantity we term as s _d ^2D. We show that this quantity is a valuable and sensitive indicator of flame turbulence interactions, as (a) it is measurable with existing experimental methodologies, and (b) because computational data, e.g. from large eddy simulations, can be post processed in an identical fashion. s _d ^2D is related (to a two-dimensional projection) of the three-dimensional flame displacement speed s _d , but artifacts due to out of plane convective motion of the flame surface and the uncertainty in the angle of the flame surface normal have to be carefully considered. Monte Carlo simulations were performed to estimate such effects for several distributions of flame front angle distributions, and it is shown conclusively that s _d ^2D is a sensitive indicator of a quantity related to s _d in the flames we study. s _d ^2D was shown to increase linearly both with turbulent intensity and with the amplitude of acousting forcing for the range of conditions studied.     

Semiempirical study of perturbations of the Landé g factors of electronic-vibrational-rotational levels of hydrogen: II. i 3 g − and j 3Δ g − states of the H2, HD,and D2 molecules

The values of the Landé g factors of the i ³Π _g ⁻ , v, N and j ³Δ _g ⁻ , v, N states of the H₂, HD, and D₂ molecules have been found semiempirically for the following vibrational and rotational quantum numbers: v≤3; N≤7 for H₂; N≤5 for HD; and N≤11 for D₂. These values were obtained in terms of the nonadiabatic model, which takes into account the interaction between the 3dπ³Π_g and 3dδ³Δ_g states with the same values of v and N in the approximation of pure precession, with the use of semiempirical values of the expansion coefficients of the wave functions in the Born-Oppenheimer basis determined by us previously and the results of numerical calculation of the overlap integrals of the vibrational wave functions of these states. The results obtained for the H₂ molecule are in good agreement with the data in the literature. For the i ³Π _g ⁻ and j ³Δ _g ⁻ states of the HD and D₂ molecules, the g factors were found for the first time. This made it possible to study for the first time the role of the isotopic effect in the perturbation of the dependences of the g factors of rovibrational levels on v and N for the triplet electronic states of the hydrogen molecule. It was found that the interference effects of interaction between the 3dπ³Π_g and 3dδ³Δ_g states lead both to significant differences—up to 8, 6, and 11 times for H₂, HD, and D₂, respectively (the i ³Π _g ⁻ state), 20 times for H₂ and HD, and two orders of magnitude for D₂ (the j ³Δ _g ⁻ state)—between the nonadiabatic values of the g factors and the corresponding adiabatic values for some isotopomers of the hydrogen molecule and to significant differences—up to 9 and 1.5 times for the j ³Δ _g ⁻ and i ³Π _g ⁻ states, respectively—in the nonadiabatic values of the g factors of rovibrational levels of different isotopomers of the hydrogen molecule. __________ Translated from Optika i Spektroskopiya, Vol. 96, No. 1, 2004, pp. 42–54. Original Russian Text Copyright ? 2004 by Astashkevich.     

Electronic structure and spectrum of Cr3+ in LiCaAlF6

The electronic structure and spectrum of Cr³⁺ in LiCaAlF₆ are investigated by using the discrete variatitional-local density functional (DV-LDF) method with embedded cluster model. The clusters (CrF₆)^3– withC ₃,D _3d andO _h point group symmetries embedded in the crystal are treated. The one-electron energy levels, densities of states, orbital populations, spin polarization splittings and energies of some terms are calculated. The results show that the relaxation of F^– ions around the Cr³⁺ impurity is inevitable, and that theD _3d andO _h (CrF₆)^3– clusters, with an extended bond-lengthR(Cr–F) chosen to be equal to 1.88 Å can represent this relaxation in a much better way. All the ligand-field transition energies, which are obtained from the transition-state energy and the Griffith parameters, as yielded by a restricted one-electron DV-LDF calculation, compare well with the experimental ones.     

Resonant electron impact excitation of highly charged Fe ions studied with a compact electron beam ion trap

We present extreme ultraviolet spectra of 3s3p–3s3d transitions in Fe¹⁴⁺ observed with a compact electron beam ion trap. The contributions of indirect excitation via a metastable state and resonant excitation are studied by observing the electron energy dependence of the spectra for the energy range of 60–210 eV. The results indicate that the 3s3d ¹D₂ level is directly excited from the 3s² ground state whereas the 3s3d ³D₃ level has a large contribution of the indirect excitation via the 3s3p ³P₂ metastable state. Comparisons with the theoretical excitation cross sections including MNn resonant excitations show good qualitative agreement with the experimental results for the electron energy dependent features.     

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.     

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.     

Fast-beam-spectroscopy by combined gas cell-laser excitation for cascade-free lifetime measurements of highly excited states

The fast-beam-spectroscopy is used for cascade-free high-precision lifetime measurements of highly excited atomic states, which are populated by a two-stage excitation as resulting from gas cell and laser interactions. An experimental extension of the method is presented demonstrating the selective population of high lying levels even from shorter-living intermediate states by an intracavity dye-laser excitation. A first example for this type of experiments is given for the lifetime of the Li 3d ² D level, which was determined to be τ(3² D)=14.60±0.13 ns. The appropriate experimental set-up is described in detail and an approximate expression for signal calculation is presented, by which the applicability of this method to other levels can be estimated.     

Lifetime measurements of Rydberg states in the 6snd 1 D 2-series of BaI

We have measured the lifetimes of 10 Rydberg states from 6s8d ¹ D ₂ to 6s 17d ¹D₂ in the Ba I spectrum by time-resolved recording of the exponential decay of the resonance fluorescence in an atomic beam. The excitation was performed by use of two pulsed dye lasers simultaneously pumped by one nitrogen laser. The lifetime results differ strongly from Coulomb approximation calculations and show deviations from a(n ^*)³-dependence.     

Dispersion and polarization interactions of the strontium atom

Dispersion coefficients involving the 5s ^{2 1} S ^e and 5s5p ^1,3P ^o states of strontium are determined from a large basis configuration interaction calculation. Dispersion coefficients are presented for the strontium dimer and also for strontium interactions with hydrogen and the rare gases. Polarizabilities and oscillator strengths from some low lying states are also given. The ground state polarizability and that of the 5s5p ¹P ^o and 5s4d ¹D ^e states are very similar in size.