Hyperfine structure constants and isotope shift of the levels of the configuration 4f 6 5d 6s 2 in Eu I

The hyperfine structure (hfs) and the isotope shift (IS) of transitions between metastable levels of the configuration 4f ⁷ 5d 6s and levels of the configuration 4f ⁶ 5d 6s ² of¹⁵¹Eu and¹⁵³Eu were studied by means of the high resolution laser-atomic-beam technique. New data for the hfs in¹⁵¹Eu and¹⁵³Eu were obtained as well as new and more accurate for the IS between¹⁵¹Eu and¹⁵³Eu. The measured hfs constantsA andB of the 4f ⁶ 5d 6s ² configuration allow to perform a parametric analysis using the Sandars and Beck theory. The value of the Sternheimer correction is also disscused.     

Precision measurement of the energy of the 4d 9 5s 2 2 D 5/2 metastable level in Ag I

The energy of the 4d ⁹ 5s ^{2 2} D _5/2 metastable level in Ag I, which is the upper level of the very narrow 5s ² S _1/2 – 4d ⁹ 5s ^{2 2} D _5/2 two-photon transition at 661.2 nm, has been determined from precision measurements of the wavelengths of the 206.1 nm (5s ² S _1/2 – 6p ² P ₃ ^2/0 ) and 547.5 nm (4d ⁹ 5s ^{2 2} D _5/2 – 6p ² P ₃ ^2/0 ) lines emitted from a hollow-cathode discharge. The measured energy of the 4d ⁹ 5s ^{2 2} D _5/2 level, 30 242.286(7) cm^–1, is combined with the known hyperfine splittings and the estimated¹⁰⁷Ag-¹⁰⁹Ag isotope shift to obtain accurate absolute frequencies for the hyperfine components of the 661.2 nm transition. These results should help in the detection of the narrow 661.2 nm two-photon transition, which has been proposed as a new optical frequency standard.     

Isotope shift measurements in titanium I

The use of an effusive beam of titanium atoms crossed with a CW single-mode tunable dye laser has allowed the high-resolution, Doppler-free study of the isotope shifts between⁵⁰Ti,⁴⁸Ti and⁴⁶Ti, for seven 3d ² 4s ² a³ F _J 3d ² 4s 4p z ⁵ D _J , visible transitions of Ti I. The measurements show without ambiguity the existence of a non-negligible field shift. Using the values of the nuclear radii of titanium (coming from muonic X-ray measurements), it is possible to determine the respective values of the field and mass shifts.     

Radiative recombination rates with different statistical distributions

The isotope shift and hyperfine structure in a rhenium hollow cathode discharge was studied for transitions of the type 5d ⁵6s7s 5d ⁵6s6p and 5d ⁵6s6d 5d ⁵6s6p through Doppler-free saturation absorption laserspectroscopy and high resolution interferometry. Taking configuration mixing in the lower levels of 5d ⁵6s6p under consideration, we obtain average configuration isotope shift values for 5d ⁵6s7s of –1760(100) MHz and for 5d ⁵6s6d of –1970(200) MHz. These experimental values compare extremely well with the theoretically predicted configuration isotope shifts in rhenium, based on pseudo-relativistic Hartree-Fock calculations, of –1710 MHz and –1940 MHz, resp. In addition hyperfine structure constants for rhenium levels of 5d ⁵6s6d are reported here for the first time.Research scientist from the University of Istanbul, Turkey     

The transition time for the ground state hyperfine splitting of209Bi82+

The lifetime of the excited hyperfine state of the ground state level of²⁰⁹Bi⁸²⁺ is calculated. The result of (Bi⁸²⁺)=400.09 s still exhibits a discrepancy to the experimental value ^ex=351(16) s of about 14%.     

Optical isotope shifts and changes in nuclear charge radii of stable Ti isotopes

Isotope shifts and hyperfine structures in three optical transitions of TiI have been investigated by using laser induced resonance fluorescence in a collimated atomic beam. From the isotope shifts data, changes of the mean square charge radii of the stable titanium isotopes have been determined for the first time. Using a combined analysis with muonic atom data on root mean square nuclear charge radii, improved model independent r ^21/2 values for the odd-even Ti isotopes have been obtained.     

Measurement of the transition wavelengths of the lithium resonance lines

Using laser-atomic-beam spectroscopy and a highly precise lambdameter, we have determined the transition wavelengths of the lithium resonance lines to be:⁶Li D₁: 6707.0704(5)Å,⁶Li D₂: 6707.9195(5)Å;⁷Li D₁: 6707.9241(5)Å,⁷Li D₂: 6707.7723(5)Å at spectroscopic conditions (15 °C, 760 mm Hg).     

Second-order isotope shifts in the ground configuration of Nd I

The isotope shift between all stable neodymium isotopes has been measured for 21 transitions in the Nd I spectrum by means of laser-atomic-beam absorption spectroscopy. A parametric analysis of the observed shifts in all the levels of the terms⁵ I,⁵ F, and⁵ S of the ground configuration 4f ⁴6s ² yields not only the magnetic parameterz _4f but, for the first time, also the effective electrostatic parametersa,b, andc. A more accurate value of the nuclear parameter ^148,150 (Nd)=0.369(20) fm² is obtained from the investigation of a 4f ³5d6s ²–4f ³5d6s6p transition. The comparison of non-relativistic Hartree-Fock calculations with the experimental data yields a scaling factorS _I ^* (Nd)=1.50(9) that agrees with the corresponding one from the hyperfine structure analysis.     

Laser and radiofrequency spectroscopy of the 5d 4 6s 6 D multiplet in Ta I

The hyperfine structure (hfs) of¹⁸¹Ta has been investigated using laser radio-frequency double resonance and high resolution laser spectroscopy on collimated atomic beams. The magnetic dipole and electric quadrupole hyperfine structure coupling constants of the 5d ^{4 6} s 6D _{3/2, 5/2, 7/2, 9/2} metastable states have been determined using radio-frequency spectroscopy. In the 5d ⁴ 6s ⁶ D _1/2 metastable state and the excited 5d ³ 6s 6p ⁴ D _3/2,⁶ D _{5/2, 9/2} as well as the unidentified 28 182.6 cm^–1 and 30 021.2 cm^–1 states, hfs constants have been obtained from high resolution laser spectroscopy. A radio-frequency converter has been developed in order to reach the frequency region 2.7–10 GHz.     

Hyperfine structure of atoms in combined external fields

In order to interpret experimental hyperfine spectra of the resonance lines of the alkali atoms in presence of external electric and magnetic fields in arbitrary direction relative to each other a computer programme has been developed which computes the splitting of hyperfine components of spectral lines and their expected relative transition probabilities. The computed data can be directly compared with experimental spectra taken by laser-atomic-beam spectroscopy. Splitting parameters, like hyperfine structure constants or polarizabilities, can be evaluated with the help of a fitting procedure. The theoretical approach used in the programme has rather general validity, therefore the programme can be utilized, within the validity of the applied theoretical assumptions, for any kind of atom.     

Static aspects of the fission and fusion of3He drops

Using an effective³He-³He interaction, we have investigated the fission and fusion of³He drops from a static point of view. Our calculations show that a fission barrier develops for these neutral systems, and that their saddle configurations are rather elongate. The transition from oblate to prolate shapes as a function of the angular momentumL, as well as critical values for fission and fusion are discussed for some selected cases. We show that a kind of proximity potential can be extracted from the drop-drop interaction potentials.     

Tensor polarizability of cadmium atoms in the excited state (5s5p)3 P 1

The tensor polarizability of the (5s5p)³ P ₁ level of cadmium atoms in a vapour cell were measured using level crossing technique and opto-magnetic double resonance in parallel electric and magnetic fields. The value of the tensor polarizability obtained from the level crossings is: ₂=1.33±0.04 kHz/(kV/cm)² and from the double resonance is: ₂=1.27±0.06 kHz/(kV/cm)². These results were compared with previous theoretical and experimental data of other authors.This work was supported in part by the Committee for Scientific Research under grant No. 2 0226 91 01     

On the hyperfine structure in the configuration 5f 3 6d7s 2 of neutral uranium

A Laser Induced Fluorescence experiment in an atomic beam has yielded experimental values of hyperfine structure (hfs) constants A and B for 28 low odd levels and 22 even levels, with an accuracy around 10^–5 cm^–1 for A and 10^–3 cm^–1 for B. A Condon Slater Racah parametric interpretation of the hfs data concerning 22 of these levels, on the basis of the configuration 5f ³ 6d 7s ², has provided values of monoelectronic parametersa _5f ⁰¹ ,a _5f ¹² ,a _6d ⁰¹ ,b _5f ⁰² ,b _6d ⁰² ,b _6d ¹³ . A least square fit calculation has been compared to the values deduced from Dirac-Fock monoelectronic radial integrals. The fit represents 18 A (16 B) values ranging from –0.42 to –2.96 mK (from –41 to 156 mK) with discrepancies less than 0.2 mK (8 mK).     

Doppler free “dark resonances” for hyperfine measurements and isotope shifts in Ca+ isotopes in a Paul trap

We have observed dark resonances in theA-type level structure, formed by the 4S_1/2 ground state, the 4P_1/2 excited state and the low lying metastable 3D_3/2 state in the Calcium ion, confined in a Paul radio-frequency trap. These Doppler-free and potentially very narrow resonances were used to determine the magnetic dipole hyperfine interaction constant A for the 4P_1/2 and 3D_3/2 state of⁴³Ca⁺, giving –142(8) MHz and –48.3(1.6) MHz, respectively. From measurements of the P-D (E1) and S-D (E2) transition wavelength in a mixture of⁴³Ca⁺ and⁴⁰Ca⁺ we determined the isotope shifts of these lines.     

Discrete-spectrum contribution to the Lamb-shift of the 2S and 2P hydrogenic states

A general formula due to Moses [Phys. Rev. A8, 1710 (1973)] for exact electric and magnetic multipole transition matrix elements in nonrelativistic hydrogenic atoms is reduced by carrying out additional integrations. By using the obtained reduced formula unrenormalized (finite) and renormalized Lamb-shift contributions stemming from individual discrete states as well as from the whole discrete spectrum are calculated in the case of the states 2S and 2P.     

Radiative lifetimes of the 6p 2 P 1 2/0 and 6p 2 P 3 2/0 levels in Yb II

Radiative lifetimes have been determined for the 6² P ₁ ^2/0 and 6² P ₃ ^2/0 levels in Yb II using the method of laser-induced fluorescence from sputtered metal vapour. The results, 8.0(2)ns (6² P ₁ ^2/0 ) and 6.3(3)ns (6² P ₃ ^2/0 ), are compared with lifetimes obtained from ab initio manybody perturbation calculations.     

Formation of negative ions by electron impact on SiF4 and CF4

First measurements of cross sections for the formation of negative ions by electron attachment to SiF₄ and CF₄ are reported for an electron impact energy range of 0 to 50 eV. The energies at which the various ions appear and the positions at which the ionization efficiency curves peak have been obtained and compared with previous measurements. Thermochemical data have been used to predict and identify the various channels of dissociation. Cross sections for the production of ion pairs through the process of polar dissociation have also been measured.Visiting fellow, on leave of absence from Universidade Federal de Sao Carlos, Departamento de Quimica, 13560, Sao Carlos, SP, Brazil     

Radiative lifetime determination for the 3s4p-1P1 state of magnesium using pulsed level-crossing spectroscopy

The natural radiative lifetime of the 3s4p ¹ P ₁ level of neutral magnesium was measured by pulsed level-crossing spectroscopy at the short excitation wavelength of 202.6 nm. We obtained =13.4(5) ns for this state, strongly deviating from a previous beam-foil result, but in good agreement with a multi-configuration Hartree-Fock calculation. A discussion of the applicability of the pulsed Hanle effect method is given.     

Lifetimes of the 4s4p 3 P 1 and 4s3d 1 D 2 states of Ca I

The lifetimes of the 4s4p ³ P ₁ and 4s3d ¹ D ₂ metastable states of Ca have been studied using the time-of-flight technique. Two kinds of observations were performed. First, the exponential decay of the fluorescence, using a (continuous) dc discharge for excitation and then the velocity distribution of the radiating atoms, using a pulsed discharge, were measured. From the combined results of these measurements the lifetimes were derived. The lifetimes of the 4s4p ³ P ₁ and 4s3d ¹ D ₂ states of Ca are determined to be 0.57±0.03 ms and 1.5±0.4 ms, respectively.     

Steps toward a high precision evaluation of the hyperfine interactions in neutral muonic helium

The solution of the Schrödinger equation of the neutral muonic helium is sketched by an eigenfunction expansion method: the eigenfunctions of the two Coulombic centres problem (of chargesZ ₁=2,Z ₂=–1) are used to expand the wave function. Our Born expansion method is a generalization of the Born-Oppenheimer approximation to a system in which the two centres (He, ^–) do not have a stable equilibrium distance. The adiabatic approximation is solved, upper-lower bounds on the eigenvalue are given for a number of states. The hyperfine energy corrections are calculated in general terms and are given numerically for the ground state and for the first muonically and electronically excited states in the frames of the adiabatic approximation. Our best value fails to give the observed hyperfine splitting of the ground state by some 5 × 10^–4 (2 MHz).