Lifetime measurements and calculations in La I

Radiative lifetime measurements have been performed, with a time-resolved laser-induced fluorescence technique, for 20 odd-parity levels of La I belonging to the configurations 5d ²6p, 5d6s6p and 4f5d6s. The new results are compared with the few experimental data available in the literature and with theoretical calculations including configuration interaction effects. The agreement theory-experiment is generally satisfying but discrepancies are observed for some levels emphasizing the difficulty to get a reliable theoretical model in such a heavy and complex neutral element.Received: 26 January 2004, Published online: 22 June 2004PACS: 32.70.Cs Oscillator strengths, lifetimes, transition moments - 42.62.Fi Laser spectroscopy     

Lifetime measurements in Tm I,Tm II,and Tm III by time-resolved laser spectroscopy

Natural radiative lifetimes of eight levels in Tm I ( 4f ¹³5d6p and 4f ¹²5d6s ² configurations), two levels in Tm II ( 4f ¹²5d6s configuration) and three levels in Tm III (4f ¹²5d configuration) have been measured by using time-resolved laser spectroscopy. Free thulium atoms, as well as singly and doubly ionized ions, were obtained in a laser-induced thulium plasma and the investigated states were selectively populated by a single-step excitation process with a tunable narrow-band laser pulse. Received 20 August 2002 / Received in final form 7 January 2003 Published online 4 March 2003 RID="a" ID="a"e-mail: huailiang.xu@fysik.lth.se     

Isotope shift studies in UV lines of Sm I on FTS: level isotope shifts and configuration assignments of the energy levels of neutral samarium atom

Isotope shifts in 200 spectral lines of neutral samarium atom (Sm I) in the region of 355-455 nm (28160-21970 cm^-1) have been measured using a Fourier Transform Spectrometer. Isotope shift data in 187 spectral lines of Sm I are being reported for the first time. Level isotope shifts, of 119 high odd- and 7 low even-parity energy levels have been evaluated using present isotope shift data combined with the earlier available data. These values have enabled us to check the assignments to 4f ⁶6s6p and 4f ⁵5d6s ² configurations of the odd-parity levels made earlier on the basis of parametric calculations. For several levels, the reported compositions of the mixed configuration of type [4f ⁵(⁶H⁰, ⁶F⁰) 5d6s ² + 4f ⁶(⁷F) 6s6p(³P⁰)] have been interpreted with the help of our values. 20 unassigned energy levels have been uniquely assigned to 4f ⁵5d6s ² configuration. The present study provides values of the levels, which were tentatively assigned to 4f ⁵5d ²6s and 4f ⁶5d6p configurations. We could also identify 4f ⁶5d6p configuration for 12 unassigned levels.Received: 16 December 2004, Published online: 7 September 2004PACS: 31.30.Gs Hyperfine interactions and isotope effects, Jahn-Teller effect     

Fine-structure energy levels, oscillator strengths and lifetimes in Co XV

Excitation energies from ground state for 97 fine-structure levels as well as oscillator strengths and radiative decay rates for all electric-dipole-allowed and intercombination transitions among the fine-structure levels of the terms belonging to the (1s ²2s ²2p ⁶)3s ²3p, 3s ³ p ², 3s ²3d, 3p ³, 3s3p3d, 3p ²3d, 3s3d ², 3s ²4s, 3s ²4p, 3s ²4d, 3s ²4f, and 3s3p4s configurations of Co XV are calculated, using extensive configuration-interaction (CI) wave functions, obtained with the CIV3 computer code of Hibbert. The important relativistic effects in intermediate coupling are included through the Breit-Pauli approximation via spin-orbit, spin-other-orbit, spin-spin, Darwin and mass correction terms. Small adjustments to the diagonal elements of the Hamiltonian matrices have been made. Our calculated excitation energies, including their ordering, are in excellent agreement with the experimental results and the experimentally compiled energy values of the National Institute for Standards and Technology (NIST) wherever available. The mixing among several fine-structure levels is found to be very strong, with most of the strongly mixed levels belonging to the (1s ²2s ²2p ⁶)3p ²3d and 3s3d ² configurations. The strong mixing among several fine-structure levels makes it very difficult to identify them uniquely. Perhaps, that may be the reason for the lack of both experimental and theoretical results for these levels. We believe that our extensive calculated values can guide experimentalists in identifying the fine-structure levels in their future work. From our radiative decay rates we have also calculated radiative lifetimes of some fine-structure levels. In this calculation we also predict new data for several fine-structure levels where no other theoretical and/or experimental results are available.     

Doppler limited laser spectroscopy on hafnium lines. Part II: Hyperfine structure of odd-parity levels

The hyperfine structure of selected odd-parity levels of the configurations 5d6s ^26p and 5d ^26s6p of I was studied in 10 lines lying in the red spectral region. Hyperfine spectra were obtained by the method of laser induced fluorescence in the plasma of a liquid nitrogen cooled hollow cathode discharge. The observed hyperfine structure constants A and B, together with results from earlier studies were analyzed by means of a parametric method. The interpretation has been carried out based on a refined multiconfigurational fine structure calculation including the main Rydberg series configurations mutually interacting. The set of fine structure parameters as well as the leading eigenvector percentages of levels relevant for this paper are given. The following single electron hfs parameters were deduced for : , ,, for the lowest configuration. Received: 16 November 1998 / Received in final form: 5 February 1999     

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 studies of rhenium by laser optogalvanic spectroscopy

Doppler-limited high resolution laser optogalvanic spectra of six transitions of rhenium lying in the range 560–620 nm have been recorded. Isotope shifts between the two natural isotopes of rhenium,¹⁸⁵Re and¹⁸⁷Re, have been calculated in all the six transitions. Hyperfine coupling constants for eight levels belonging to the configurations 5d ⁵6s ², 5d ⁶6s, 5d ⁴6s ²6p and 5d ⁵6s6p are reported. Wherever possible our constants are compared with those given by others.     

Energies and Landé factors for some excited levels in Lu I (<Emphasis Type="Italic">Z</Emphasis> = 71)

We have calculated relativistic energies and Landé factors for 5d6s ², 5d ²6s, 6s6p ², 6s ²7s, 5d ³, 5d6s7s, 6s ²6p, 5d6s6p, 5d ²6p and 6s ²7p excited levels outside the core [Xe]4f ¹⁴ in neutral lutetium (Lu I, Z = 71). These calculations are based on the multiconfiguration Hartree-Fock (MCHF) method, within the framework of the Breit-Pauli relativistic corrections. Moreover, the results obtained have been compared with other works.     

The observed and predicted spectrum of neutral chromium: Cr I

The spectrum of neutral chromium (Cr I) has been investigated in detail. It is basically a sixelectron system, exhibiting a very complex structure with its ground configuration 3d ⁵4s. The low lying excited configuration is 3 d ⁵4p and the core excitation leads to 3d ⁴4s4p. Further excitations of these configurations give rise to 3d ⁵4d, 3d ⁴4s ². In the past, a large number of levels have been reported without any satisfactory theoretical support. In the present work we have observed the spectrum of Cr on a 35 ft grating of our laboratory in the wavelength region 4800–5500 ? and have carried out configuration interaction (CI) calculations for abovementioned configurations. Known levels have been used to optimize the energy parameters of least squares fitted parametric calculations. These parameters were used to predict the unknown levels more precisely. Among 1014 energy levels, 652 levels are newly predicted (208 listed in the tables and 444 levels lying above 66500 cm⁻¹ are available privately on demand).     

High resolution measurements of the hyperfine structure in 10 levels of Tm I

High resolution laser spectroscopy has been performed on an atomic beam of thulium. Accurate values for the magnetic dipole coupling constants of 9 excited levels belonging to the 4f¹³ 6s6p and 4f¹²5d6s² configurations and of the metastable level at 8771 cm^?1 belonging to the 4f¹³6s² ground state configuration have been obtained.     

Radiative lifetime measurements in neutral zirconium using time-resolved laser induced fluorescence in supersonic free-jet

Radiative lifetimes of 20 odd-parity excited energy levels in Zr I, out of which 10 for the first time, have been investigated in the energy range 17 400-29 300 cm⁻¹. The levels belong to the 4d²5s5p and 4d³5p electronic configurations. Time-resolved laser-induced fluorescence spectroscopy technique in supersonic free-jet has been employed in the present work to circumvent the effects of collision in lifetime measurements.     

Excitation of even levels of erbium atoms without a change in the number of 4<Emphasis Type="Italic">f</Emphasis> electrons

The excitation of even levels of erbium atoms by slow electrons that occurs without a change in the number of electrons in the 4f shell is experimentally studied. The levels investigated belong to the 4f ¹²6s7s, 4f ¹²5d6s, 4f ¹²6s6d configurations. The cross sections measured at an electron energy of 30 eV lie within the range (0.2–18) × 10^?18 cm².     

Electronic structure of Ce and Sm in hydrides and the 4f collapse in YbHx

The population of the 4f, 5d, and 6s shells of rare-earth atoms in RH_x hydrides (R=Ce, Sm, Yb; x≈2–3) has been studied by the x-ray line-shift method. The population of the 5d and 6s shells of Ce and Sm atoms, and the charge on them in metals and hydrides, were determined from experiment and calculated within the Hartree-Fock-Dirac (Koopmans) model. The decrease of the charge on Ce and Sm revealed upon transition from the metal to the hydride argues unambiguously for the anionic (hydride) model. In YbH_x with x⩾2, the structural transition is accompanied by a strongly pronounced electronic transition from divalent to a noninteger-valence state . Fiz. Tverd. Tela (St. Petersburg) 40, 1393–1396 (August 1998)     

Changes in mean-square nuclear charge radii in Er from optical isotope shifts by laser-atomic-beam spectroscopy

High-resolution laser-atomic-beam spectroscopy has been applied to investigate transitions 4f ¹² 6s ²?4f ¹¹ 5d6s ² and transitions starting from metastable states of the configuration 4f ¹¹ 5d6s ² of Er I. Precise values for the transition isotope shifts and for the hyperfine constants of 10 levels belonging to the configuration 4f ¹¹ 5d6s² and 9 levels belonging to high lying even-parity levels have been determined. From the isotope shift data relative changes of mean-square nuclear charge radiiδ 〈r ²〉 for all the stable Er isotopes have been deduced: ¦168,170¦ 1, ¦166,168¦ 0.984(15), ¦164,166¦ 0.984(15), ¦162,164¦ 1.198(18), ¦166,167¦ 0.3357(50). Absoluteδ 〈r ²〉 values have been obtained by calibrating the optical data with a value from muonic x-ray spectroscopy: ¦168,170¦ 0.121 (10) fm². The odd-even staggering parameter for¹⁶⁷Er has been determined: 0.683(10). Our results are compared with experimental data from electronic x-ray spectroscopy and data from calculations with the extended liquid-drop and the droplet model.     

High-lying odd configurations of quintuply ionized bismuth (Bi VI)

The spectrum of Bi VI in a wavelength region of 177–431 Å was studied. The transitions from the levels of the interacting configurations 5d ⁸6s6p+5d ⁹7p+5d ⁹5f+5d ⁹6f to the levels of the 5d ¹⁰ and 5d ⁹6s configurations were analyzed. 174 spectral lines were identified, and 79 new levels of high-lying odd configurations of Bi VI were found.     

Recent hyperfine structure investigations in the configurations 4f 136s 2, 4f 136s6p,and 4f 125d6s 2 of Tm I

By use of optical hyperfine structure investigations in the Tm I spectrum theA- values of 20 levels of the configurations 4f ¹³ 6s 6p and 4f ¹² 5d 6s ² and theA-value of 4f ¹³ 6s ^{2 2} F _5/2 were determined very accurately. These data and tenA-factors from former experiments are used for theoretical calculations. 30A-factors have been interpolated from intermediate coupling wave functions using 9 effective mono-electronic parameters. The r.m.s. deviation between experimental and theoreticalA- values amounts to 0.5 10^?3 cm^?1 and represents 3/100 of the average value of the measuredA-factors.     

Analysis of the spectrum of the Zn-like Kr VII ion: Highly excited 4<Emphasis Type="Italic">p</Emphasis>4<Emphasis Type="Italic">d</Emphasis> and 4<Emphasis Type="Italic">p</Emphasis>5<Emphasis Type="Italic">s</Emphasis> configurations

The spectrum of the Zn-like Kr VII ion, excited in a capillary discharge and recorded with a high resolution in the wavelength range of 300–1000 Å, was studied. Previously performed identification of the transitions from the levels of the 4s4f, 4s5s, 4s5p, and 4s5d configurations is confirmed and extended, and the energies of these levels are specified. The (4p ²+4s4d)?4p4d and (4p ²+4s5s)?4p5s transitions are identified for the first time, and the energies of all the levels of the 4p4d and 4p5s configurations are determined. The results of the analysis performed are confirmed by semiempirical calculations in terms of the Hartree-Fock method. These results are also shown to conform to the experimental data obtained for lighter ions of the Zn I isoelectronic sequence.     

Tensor polarizabilities of levels of the configurations 4f 13 6s6p and 4f 12 5d6s 2 in thulium I

The level-crossing technique with parallel electric and magnetic fields was used to measure the tensor polarizabilities of six levels of the configuration 4f ¹³ 6s6p + 4f ¹² 5d6s ² in the Tm I-spectrum. Using intermediate coupling wave functions given by Camus and the experimental values of the tensor polarizabilities, the radial integrals for electric dipole transitions from levels of the configuration 4f ¹³6s6p + 4f ¹²5d6s ² to levels of the configuration 4f ¹³ 5d6s + 4f ¹² 6s ²6p have been determined. The results areI(4f ¹³6s6p,4f ¹³5d6s)=1.98(45)ea ₀ andI(4f ¹²5d6s ²,4f ¹²6s ²6p) = 0.88(25)ea ₀. A comparison between the experimental and the calculated values of the tensor polarizabilities shows an excellent agreement, provided that these radial integrals and the radial integrals for the electric dipole transitions to the ground state configuration 4f ¹³6s ² as determined by Wallenstein from lifetime measurements are used in the calculation, instead of radial integrals computed by Camus with Hartree-Fock wave functions.     

Radiative lifetimes and transition probabilities in Ta I

Radiative lifetimes of 14 odd-parity Ta I levels, belonging to the 5d³6s6p and 5d⁴6p configurations in the energy range from 30 664 to 45 256 cm^-1, have been measured using the time-resolved laser-induced fluorescence technique. Extensive calculations, taking configuration interactions and core-polarisation effects into account, are able to reproduce in a satisfying way the available experimental results but suffer from the rather fragmentary knowledge of the level structure of this atom. New transition probabilities are deduced for a set of strong lines depopulating the levels investigated experimentally in the present work.     

Additional symmetry for the electronic shell in its ground state and many-electron effects

The additional symmetry for the properties related to the ground state of the atom is considered taking into account many-electron effects. Calculations of the I _4f, I _3d,I _2p,I _3p binding energies, 4f ^N-15d - 4f^N system differences and 2p, 3p electron affinities in the second order of perturbation theory and in the configuration interaction approximation have been performed for the ground configurations with one open shell. The analysis of separate many-electron corrections for these quantities and their variation along the sequences of atoms and ions shows that the main corrections maintain the considered symmetry. Received 18 January 1999 and Received in final form 17 July 1999