Odd-parity Levels Research Articles

New even parity autoionisation levels of UI

Even parity autoionisation levels of atomic uranium are investigated in the energy region 51425–51760 cm−1 by two-colour three-photon ionisation spectroscopy in an atomic beam using a time of flight mass spectrometer and in a hollow cathode discharge source using photoionisation optogalvanic spectroscopy. Analysis of the photoionisation spectrum has resulted in identification of 26 new levels and confirmation of 24 levels reported earlier. In addition 9 odd parity levels in the energy region 34525–34860 cm−1 are confirmed.

Vibrational Levels of Ar4: New Odd-Parity Bosonic States

Vibrational levels of Ar4 are computed using the Lanczos algorithm and a large basis set. We find both even- and odd-parity states with wave functions that are invariant with respect to permutations of the Ar atoms. The odd-parity bosonic levels have not been computed previously. The even-parity levels are close to those obtained using the correlation-function Monte Carlo method (CFMC).

Infrared spectrum and revised energy levels for neutral krypton

We observed the spectrum of neutral krypton (Kr I) in its naturally occurring isotopic mixture as emitted by a microwave-excited electrodeless discharge lamp with the National Institute of Standards and Technology (NIST) 2 m Fourier transform spectrometer (FTS). The spectra cover the region from 6699 to 12 200 Å with a resolution of 0.01 cm−1 and the region from 9000 to 47 782 Å with a resolution of 0.007 cm−1. We present a line list that includes more than 630 classified lines, about 290 newly observed, and provides an accurate and comprehensive description of the infrared spectrum. The response of the FTS was characterized by using a radiometrically calibrated tungsten strip lamp to obtain relative intensities accurate to 10% or better over the entire spectral range for lines with good signal-to-noise ratio (SNR). All eight levels of the 4s2 4p5 (2P3/2)6g configuration have been located as well as one previously unknown level of the 4s2 4p5 (2P3/2)6f configuration. Our new data have been combined with previous precise measurements to determine improved values for 64 even and 77 odd parity levels of Kr I.

Experimental hyperfine structure investigation of atomic La

Optogalvanic laser spectroscopy has been applied to measure the hyperfine structure of 19 spectral lines of La I in the wavelength regions from 570 to 590 nm and 700 to 825 nm. Experimental hyperfine structure constants A and B of the isotope139La have been measured for 16 levels of odd parity. From those values six magnetic dipole and ten electric quadrupole constants have been determined for the first time. Some disagreements with previously obtained values are discussed.

Improved Laboratory Transition Probabilities for Hf ii and Hafnium Abundances in the Sun and 10 Metal‐poor Stars

Radiative lifetimes from laser-induced fluorescence measurements, accurate to ~±5%, are reported for 41 odd-parity levels of Hf II. The lifetimes are combined with branching fractions measured using Fourier transform spectrometry to determine transition probabilities for 150 lines of Hf II. Approximately half of these new transition probabilities overlap with recent independent measurements using a similar approach. The two sets of measurements are found to be in good agreement for lines in common. Our new laboratory data are applied to refine the hafnium photospheric solar abundance and to determine hafnium abundances in 10 metal-poor giant stars with enhanced r-process abundances. For the Sun we derive log ε(Hf) = 0.88 ± 0.08 from four lines; the uncertainty is dominated by the weakness of the lines and their blending by other spectral features. Within the uncertainties of our analysis, the r-process-rich stars possess constant Hf/La and Hf/Eu abundance ratios, log ε(Hf/La) = -0.13 ± 0.02(σ = 0.06) and log ε(Hf/Eu) = +0.04 ± 0.02 (σ = 0.06). The observed average stellar abundance ratio of Hf/Eu and La/Eu is larger than previous estimates of the solar system r-process-only value, suggesting a somewhat larger contribution from the r-process to the production of Hf and La. The newly determined Hf values could be employed as part of the chronometer pair, Th/Hf, to determine radioactive stellar ages.

Lifetime measurements in neutral and singly ionized vanadium

Radiative lifetimes of ten odd-parity levels of V I belonging to the 3d34s4p and 3d44p configurations and of 11 odd-parity levels of V II belonging to the 3d34p configuration are reported. The lifetimes were measured with use of single-step excitation and time-resolved fluorescence spectroscopy. The neutral and singly ionized vanadium atoms were produced in a laser-induced vanadium plasma.

New levels and hyperfine structure evaluation in neutral praseodymium

Fifty seven new electron levels of odd parity in neutral praseodymium are presented. These have been found on the basis of an analysis of hitherto unclassified spectral lines with the method of laser-induced fluorescence (LIF). For all the levels the hyperfine magnetic dipole interaction constants A have been determined.

Improved atomic data for iridium atom (Ir I) and ion (Ir II) and the solar content of iridium

From a combination of radiative lifetime measurements, performed with a time-resolved laser-induced fluorescence technique, for nine odd-parity levels of Ir I and four odd-parity levels of Ir II and branching fraction calculations, extended sets of transition probabilities have been derived for transitions of astrophysical interest. The new results are compared with the few experimental data available in the literature and a good agreement is found. They extend considerably the previous sets of transition probabilities available in the literature. Implications of the new results regarding the solar content of iridium are briefly discussed.

New and improved experimental oscillator strengths in Zr II and the solar abundance of zirconium

Using the Fourier Transform Spectrometer at Lund Observatory, intensity calibrated spectra of singly ionized zirconium have been recorded and analyzed. Oscillator strengths for 263 Zr II spectral lines in the region 2500-5400 angstrom have been derived by combining new experimental branching fractions with previously measured radiative lifetimes. The transitions combine 34 odd parity levels with 29 low metastable levels between 0 and 2.4 eV. The experimental branching fractions have been compared with theoretical values and the oscillator strengths with previously published data when available. The oscillator strengths have been employed to derive the solar photospheric Zr abundance based on both 1D and 3D model atmospheres. Based on the seven best and least perturbed Zr II lines in the solar disk-center spectrum, we determine the solar Zr abundance to log epsilon(Zr) = 2.58 +/- 0.02 when using a 3D hydrodynamical solar model atmosphere. The new value is in excellent agreement with the meteoritic Zr abundance. (Less)

Transition probabilities and lifetimes in gold (Au I and Au II)

Radiative lifetimes of three odd-parity levels of neutral gold (Au I) and one odd-parity level of singly ionized gold (Au II), measured using the time-resolved laser-induced fluorescence technique, have allowed the testing of the reliability of a relativistic Hartree–Fock model of the atomic structure taking configuration interaction and core-polarization effects into account. The importance of the inclusion of the latter effects in the calculations is emphasized. The laser-induced fluorescence lifetimes, combined with the theoretical branching fractions, have allowed us to deduce oscillator strengths for six 5d96s2–5d96s6p and 5d106s–5d96s6p transitions of Au I and for sixty-three 5d96s–5d96p, 5d96p–5d97s and 5d10–5d96p UV transitions of Au II.

Radiative lifetime measurements and semi-empirical transition probability calculations in neutral rhenium

Radiative lifetimes of 11 odd-parity levels of neutral rhenium (Re I) were measured using time-resolved laser-induced fluorescence techniques. For ten levels, there were no previous results available. The new results have been used to assess the accuracy of calculations with a Hartree–Fock-plus-relativistic-corrections model that takes configuration interaction and core-polarization effects into account and they have allowed the deduction of reliable semi-empirical transition probabilities for 81 Re I lines.

Investigation of the hyperfine structure of Ta I lines (X)

We report the discovery of 23 new energy levels of even parity and 21 new energy levels of odd parity of the tantalum atom. The results given here are based on investigations of the hyperfine structure of 221 new spectral lines of the tantalum atom (Ta I) by means of laser spectroscopic methods, detecting laser-induced fluorescence. The excitation wavelengths were extracted from high-resolution Fourier transform spectra.

Radiative lifetimes, branching fractions and oscillator strengths in Pd I and the solar palladium abundance

Transition probabilities have been derived for 20 5s−5p transitions of Pd I from a combination of radiative lifetime measurements for 6 odd-parity levels with time-resolved laser-induced fluorescence spectroscopy and of branching fraction determination using a hollow cathode discharge lamp. Additional oscillator strengths for 18 transitions have been determined from measured lifetimes and theoretical branching fractions obtained from configuration interaction calculations with core-polarization effects included. These new results have allowed us to refine the palladium abundance in the solar photosphere: APd = 1.66 ± 0.04, in the usual logarithmic scale, a result in close agreement with the meteoritic value.

Improved Laboratory Transition Probabilities for Smiiand Application to the Samarium Abundances of the Sun and Threer‐Process–rich, Metal‐poor Stars

Radiative lifetimes, accurate to ±5%, have been measured for 212 odd-parity levels of Sm II using laser-induced fluorescence. The lifetimes are combined with branching fractions measured using Fourier transform spectrometry to determine transition probabilities for more than 900 lines of Sm II. This work is the largest scale laboratory study to date of Sm II transition probabilities using modern methods. This improved data set has been used to determine a new solar photospheric Sm abundance, log = 1.00 ± 0.03, from 26 lines. The spectra of three very metal-poor, neutron-capture-rich stars also have been analyzed, employing between 55 and 72 Sm II lines per star. The abundance ratios of Sm relative to other rare earth elements in these stars are in agreement and are consistent with ratios expected from rapid neutron-capture nucleosynthesis (the r-process).

Relativistic many-body calculations of electric-dipole lifetimes, transition rates and oscillator strengths for 2l−13l′ states in Ne-like ions

Transition rates, oscillator strengths and line strengths are calculated for electric-dipole (E1) transitions between odd-parity 2s22p53s, 2s22p53d and 2s2p63p states and even-parity 2s22p53p, 2s2p63s and 2s2p63d states in Ne-like ions with the nuclear charges ranging from Z = 14 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s22s22p6 Dirac–Fock potential. First-order RMBPT is used to obtain intermediate coupling coefficients and second-order RMBPT is used to calculate transition matrix elements. Contributions from negative-energy states are included in the second-order E1 matrix elements to ensure the gauge independence of transition amplitudes. Transition energies used in the calculation of oscillator strengths and transition rates are from second-order RMBPT. Lifetimes of the 16 even-parity and 18 odd-parity levels are given for Z = 14–100. Transition rates, line strengths and oscillator strengths are compared with critically evaluated experimental values and with results from other recent calculations. These atomic data are important in the modelling of L-shell radiation spectra of heavy ions generated in electron beam ion trap experiments and in L-shell diagnostics of plasmas.

Two-color photoionization spectroscopy of uranium in a U–Ne hollow cathode discharge tube

A U–Ne hollow cathode discharge tube is used as a source of uranium atomic vapors as well as a photoelectron/photoion detector for carrying out two-color three-photon photoionization spectroscopy of uranium. Using the uranium excitation transition 0 cm−1 (5L60) → 16 900.38 cm−1 (7M7) at 591.5-nm laser wavelength as a first step transition and scanning the wavelength of a second laser from 558 to 568 nm, high-lying odd-parity atomic levels of uranium are studied in the energy region 34 500–34 813 cm−1. All the expected 21 odd-parity atomic levels identified by various researchers in this region are observed in a single spectrum, demonstrating the high sensitivity achieved therein. In addition to this, we have identified eight autoionization resonances of uranium starting from its odd-parity atomic level at 33 801.06 cm−1 pumped by two-photon excitation. Four out of these eight autoionization resonances are observed for the first time.

Improved Laboratory Transition Probabilities for Ptiand Application to the Platinum Abundances of BD +17o3248 and the Sun

Radiative lifetimes, accurate to ±5%, have been measured for 58 odd-parity levels of Pt I using laser-induced fluorescence. The lifetimes were combined with branching fractions measured using grating and Fourier transform spectrometry to determine transition probabilities for 127 lines of Pt I. The new Pt lifetime measurements were found to be in good agreement with previous but less extensive measurements based on laser-induced fluorescence. The new branching fraction measurements were found to be in fair agreement with one earlier study. Absolute atomic transition probabilities from the new measurements were used to determine the platinum abundance in the metal-poor Galactic halo star BD +17°3248. An attempt to refine the solar photospheric abundance of platinum was unsuccessful; the single Pt I line used in an earlier abundance determination was found to be even more severely blended than expected from earlier work.

Investigation of the Hyperfine Structure of Ta I Lines (IX)

We report the discovery of 25 previously unknown energy levels of even parity and 3 previously unknown energy levels of odd parity of the tantalum atom, including the last two unknown levels with energy values below 32500 cm-1. Thus, below 32500 cm-1, all levels predicted by theory have now been observed. These results are based on investigations of the hyperfine structure of 126 new spectral lines of the tantalum atom (Ta I) by means of laser spectroscopy. The observation of laser-induced fluorescence further led to the classification of 159 spectral lines. Additionally, 235 lines, observed in high resolution Fourier transform spectra, were classified by their wave numbers and their characteristic hyperfine patterns.

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 $\Delta \sigma^{148,154}$ 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, $\Delta T^{148,154}$ 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 $\Delta T^{148,154}$ 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 $\Delta T^{148,154}$ values. 20 unassigned energy levels have been uniquely assigned to 4f 55d6s 2 configuration. The present study provides $\Delta T^{148,154}$ 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.

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(2)6p, 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.