Ultracold atoms confined in a dipole trap are submitted to a potential whose depth is proportional to the real part of their dynamic dipole polarizability. The atoms also experience photon scattering whose rate is proportional to the imaginary part of their dynamic dipole polarizability. In this article we calculate the complex dynamic dipole polarizability of ground-state erbium, a rare-earth atom that was recently Bose-condensed. The polarizability is calculated with the sum-over-state formula inherent to second-order perturbation theory. The summation is performed on transition energies and transition dipole moments from ground-state erbium, which are computed using the Racah-Slater least-square fitting procedure provided by the Cowan codes. This allows us to predict 9 unobserved odd-parity energy levels of total angular momentum J=5, 6 and 7, in the range 25000-31000 cm-1 above the ground state. Regarding the trapping potential, we find that ground-state erbium essentially behaves like a spherically-symmetric atom, in spite of its large electronic angular momentum. We also find a mostly isotropic van der Waals interaction between two ground-state erbium atoms, characterized by a coefficient C_6^{iso}=1760 a.u.. On the contrary, the photon-scattering rate shows a pronounced anisotropy, since it strongly depends on the polarization of the trapping light.Comment: 15 pages, 5 figure

Because of the confusion between two low odd levels 1218 cm-1 apart, the complete system of levels of Nd II built on the core f3 had to be revised with the help of the 144Nd-150Nd isotope shift. The lowest odd level f3d2 6M13/2 is now at 8009.810 cm-1, 96 levels have been shifted and 126 new levels have been found. The new identifications rely upon parametric studies of the sub-configurations 4f35d6s + 4f3(4I)5d2 + 4f4(5I)6p (115 interpreted levels) and 4f3(4I)5d6p + 4f3(4I)6s6p (124 interpreted levels).

Spectra of multicharged ions have been analyzed for all stable elements in the period from Z = 37 (Rb) to Z = 50 (Sn), in the region of n = 4, Δn = 0 transitions. The transition arrays (4s2 + 4p2 + 4s4d)-4s4p, 4s4f and 3d94s, 3d94d-3d94p have been identified in zinc-like and nickel-like ions respectively, with the help of the ab initio relativistic parametric potential method and of the Slater-Condon method with generalized least-squares fits of energy parameters.

Abstract. The efficiency of optical trapping of ultracold atoms depend on the atomic dynamic dipole polarizability governing the atom-field interaction. In this article, we have calculated the real and imaginary parts of the dynamic dipole polarizability of dysprosium in the ground and first excited level. Due to the high electronic angular momentum of those two states, the polarizabilities possess scalar, vector and tensor contributions that we have computed, on a wide range of trapping wavelengths, using the sum-over-state formula. Using the same formalism, we have also calculated the C 6 coefficients characterizing the van der Waals interaction between two dysprosium atoms in the two lowest levels. We have computed the energies of excited states and the transition probabilities appearing in the sums, using a combination of ab initio and least-square-fitting techniques provided by the Cowan codes and extended in our group. Regarding the real part of the polarizability, for field frequencies far from atomic resonances, the vector and tensor contributions are two-order-of-magnitude smaller than the scalar contribution, whereas for the imaginary part, the vector and tensor contributions represent a noticeable fraction of the scalar contribution. This offers the possibility to control the decoherence and trap losses due to spontaneous emission.

A recent breakthrough in the analysis of Nd IV resulted in the establishment of 37 energy levels of the ground configuration 4f3. We report here the completion to all 41 levels of this configuration. Wavelength measurements extended to 2800 Å and in higher excitation conditions lead to the classification of 1426 lines involving the excited configurations 4f25d, 4f26p, 4f26s. Owing to configuration mixing between 5p64f26p and the core-excited 5p54f4, numerous 5p64f25d–5p54f4 transitions, normally dipole-forbidden, are observed. Altogether 111 odd parity levels and 121 even parity ones have been established. Their parametric least-squares fits have rms deviations of 91 cm−1 and 37 cm−1, respectively. The interaction 5p64f25d–5p54f35d has an impact on the 4f3–4f25d transition probabilities computed by means of the Cowan codes. Theoretical values of lifetimes are reported for all the even parity levels.

Spectra of gold, emitted from a hollow-cathode discharge, have been recorded with the Lund Fourier transform spectrometer in the region 1800-8000 Å. Complementary photographic spectrograms in the region 800-1900 Å have been obtained using the 10.7 m normal incidence spectrograph at Observatoire de Paris, Meudon. The term analysis has yielded 75 new energy levels of Au II, and improved values are given for the previously known levels of the 5d10, 5d96s, 5d86s2, 5d97s, 5d96d, 5d96p, 5d86s6p and 5d97p configurations. The new levels belong to the 5d86s2, 5d96d, 5d98s, 5d86s6p, 5d97p and 5d76s26p configurations. About 450 identified Au II lines with a wavelength uncertainty of about 1 mÅ are reported. The energy level structure has been studied by using the Slater-Condon parametric method. The ionization limit has been determined to 162950 ± 200 cm−1.

A new set of transition probabilities is derived for many transitions of Ce II of astrophysical interest. A relativistic Hartree-Fock method, combined with a least-squares ¢tting of the available experimental levels, including a number of newly determined values, has been used for the determination of the eigenfunctions and eigenvalues. Con¢guration interaction and corepolarization e¡ects have been introduced in the calculations. The derived oscillator strengths lead to a new value of the cerium abundance in the solar photosphere, A Ce 1:70 AE 0:04 (in the usual logarithmic scale) which is somewhat larger but in reasonable agreement with the meteoritic result.*

Tungsten spectra excited in the vacuum sparks of different setups and electric circuits were recorded on two high-resolution vacuum spectrographs. For the region 190-500 Å, a 10 m normal incidence spectrograph with a 3600 lines/mm grating was used in the Meudon Observatory. In the region below 350 Å, a set of spectra was produced using a 3 m grazing incidence spectrograph with a 3600 lines/mm grating in the Institute of Spectroscopy in Troitsk. A total of 187 lines in the region 160-271 Å were identified as transitions to the low-lying odd configurations 4f 13 5s 2 5p 6 and 4f 14 5s 2 5p 5 from the interacting excited even 4f 12 5s 2 5p 6 5d + 4f 13 5s 2 5p 5 (5d + 6s) + 4f 14 5s 2 5p 4 (5d + 6s) + 4f 14 5s5p 6 configurations. It was found that 4f 13 5s 2 5p 6 2 F 7/2 is the ground level of W VIII. The fine structure splitting and relative positions of the odd terms were established, and 98 levels of the excited even configurations were found.