T.J. Scholl

Oscillator strength measurements in Pr II with the fast-ion-beam laser-induced-fluorescence technique

The spontaneous-emission branching fractions of 32 levels of Pr II were measured by the fast-ion-beam laser-induced-fluorescence technique. The levels studied had energies from 21 500 to 29 000 cm 1 , and the decay branches detected were in the range from 250 to 850 nm. The experimental uncertainties are within 10%. Using our previously measured radiative lifetimes, we determined the Einstein A coefficients and oscillator strengths for 260 transitions. The results are important for stellar elemental abundance determinations.

High-resolution study of the B2Σu+−X2Σg+ system of 14N2+ and 15N2+

Abstract The (0, 1) band of the B 2 Σ u + − X 2 Σ g + system of 14 N 2 + and 15 N 2 + has been studied under high resolution using the method of fast-ion-beam laser spectroscopy. Transition wavenumbers have been measured with an absolute accuracy of −1 . We have also applied the laser-rf-laser double resonance method to 15 N 2 + for the first time. The frequencies of hyperfine components of fine-structure rf transitions in 10 rotational levels of the X 2 Σ g + v ″ = 1 state have been measured absolutely to 10 kHz. Because the hyperfine structure was resolved in both the optical and rf transitions, we were able to observe a hyperfine anomaly in the X 2 Σ g + ground state, and changes in the hyperfine splitting of the B 2 Σ u + state and the neighboring A 2 Π u state arising from strong perturbations between them. Many molecular parameters have been measured for the first time or with greatly improved precision.

Broadband precision wavelength meter based on a stepping Fabry-Pérot interferometer

We have constructed a broadband apparatus for wavelength metrology capable of absolute accuracy at a level of better than 2 parts in 109. An evacuated plane-parallel Fabry–Perot interferometer with continuously adjustable mirror separation is used to compare the wavelength of a single-frequency tunable laser with that of an iodine-stabilized HeNe laser used as a wavelength standard. This work details apparatus construction, a thorough investigation of systematic errors, and data analysis. The wavelengths of five Doppler-free 130Te2 transitions in the region from 475.6 to 490.8 nm have been measured and are found to be in excellent agreement with previous measurements. In addition, the wavelengths of five previously unmeasured 130Te2 transitions spanning the region from 424.9 to 462.3 nm have been determined for use as new reference wavelength standards.

Measurement of radiative lifetimes in Nd II

We have measured the radiative lifetimes of 82 levels of Sm II using the beamlaser method. The levels studied had term energies up to ∼29 600 cm−1 and lifetimes in the range 9–190 ns. Experimental uncertainty was less than 7%, with a typical value of 1.6%. We have used these lifetimes to update transition probabilities for 35 transitions in the wavelength range 363–771 nm, which are useful for stellar abundance determinations. PACS Nos.: 32.70Cs, 95.30Ky Résumé : Nous avons mesurés les temps de vie de 82 niveaux du Sm II en utilisant la méthode laser-faisceau. Les niveaux étudiés avaient des termes dont l’énergie allait jusqu’à 29 600 cm−1 et des temps de vie allant de 9 à 190 ns. L’erreur expérimentale était plus petite que 7 %, avec une valeur moyenne de 1.6 %. Nous avons utilisé ces temps de vie pour améliorer les valeurs des probabilités de transition de 35 transitions dans le domaine 363–771 nm, qui sont très utiles pour déterminer les abondances stellaires. [Traduit par la Rédaction]

Fast-ion-beam laser-fluorescence measurements of oscillator strengths in the lanthanides

Atomic oscillator-strength data are of great interest to astronomers studying photospheric chemical abundances, stellar interiors and nucleosynthesis. We review the classic methods of measurement and then discuss our approach, which is based on fast-ion-beam laser-fluorescence techniques for both lifetime and branching-fraction measurements. Recently obtained large data sets in singly ionized lanthanides are discussed, with several examples illustrating the major advantages of this method: unambiguous identification of the upper level of a transition and greatly reduced spectral line blending.