The sodium D2-line in electric and magnetic fields

The influence of perpendicularly crossed electric and magnetic fields of comparable strength on the hyperfine components of the sodium D₂-line was studied by means of laser-atomic-beam spectroscopy. The observed spectra show changes in the polarization type (, ) when one of the fields becomes dominant relative to the other. Theoretical calculations confirm the experimental observations.     

The sodium D2-line in electric and magnetic fields

The splitting of the hyperfine structure of the D₂ line of the sodium atom was investigated under the influence of simultaneously acting parallel magnetic and electric fields of comparable strength. The experimental spectra were taken by laser-atomic-beam spectroscopy. Theoretical spectra obtained by quantum mechanical calculations agree very well with the experimentally observed spectra, therefore allowing their clear interpretation, especially at anticrossing regions.     

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).     

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.     

Measurement of the polarizabilities ofn 2 D Rydberg states of cesium

The tensor polarizabilities of thenD states of cesium withn=22–55 were determined by Doppler-free two-photon absorption spectroscopy. In general the results are in agreement with theoretical predictions. The large discrepancy between them forn>45 is discussed.Sponsored by NSFC     

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     

Experimental ground stateg J-factor of Ba+ in a Penning ion trap

We observed the Zeeman-splitting of the 6S _1/2 – 6P _1/2 resonance transition of Ba⁺-ions (493.4 nm) in a 6T magnetic field. The ions were stored in a Penning quadrupole trap. We polarized the ground state by optical pumping and in a microwave-optical double resonance experiment we measured the ground state Zeeman-splitting. From the resonance frequency and the cyclotron frequency of electrons stored in the same trap we derived theg-factor of the 6S _1/2 state. The result isg _J(6S _1/2)=2.002 490 6(11), in reasonable agreement with recent calculations.     

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.     

Stark widths and shifts of SnI,HgII, HgIII and PbII spectral lines

Stark widths and shifts of neutral and ionized heavy atom spectral lines have been measured and calculated. The Stark parameters of three SnI (284.0, 286.3 and 303.4 nm), five HgII (226.2, 398.4, 222.5, 615.0 and 326.4 nm), two PbII (220.4 and 438.6 nm) and one HgIII (235.4 nm) spectral lines were measured for the first time except the Stark widths of one HgII (398.4 nm) and one PbII (438.6 nm) line. Stark width values for a number of corresponding transitions were calculated on the bases of semiclassical and semiempirical formulae.     

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.     

Regularity and chaos in the center of mass motion of the hydrogen atom in a magnetic field

What does the center of mass motion of the hydrogen atom in a magnetic field look like? Is it similar to the uniform straight-lined motion of the field-free case or does is perform only tiny vibrations? We show that there is a great variety in the center of mass motion. For regular electronic motion only a bounded range of phase space is available for the center of mass coordinate. There exist many different types of regular center of mass behavior according to the values of the magnetic field strength, energy and angular momentum. At the onset of chaos in the electronic motion a prominent transition to chaos in the center of mass motion is observed. In the fully chaotic regime the trajectories of the center of mass exhibit many properties of a random motion and fill up the unbounded coordinate space. In particular, we obtain a linear diffusion law for the spreading of an ensemble of center of mass trajectories.     

Collisional excitation transfer between lithium isotopes

Excitation transfer between the 3S _1/2 states of the lithium isotopes⁶Li and⁷Li is measured in a thermionic diode. The 3S level is excited by off-resonant two-photon transitions with a single mode ew laser. The relative densities of the directly excited and collisionally populated levels are probed by further laser excitation to the 12P levels. An energy transfer cross section of 585 Ų±160 Ų is found at the experimental temperature of about 850 K. A simple semiclassical calculation yields a cross section of 450 Ų.     

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     

Tensor polarizabilities of the 4f 7(8 S)5d6s 2 9 D 2,3,4,5,6 levels in Gd I

The optical pumping method with rf detection and the nonlinear level crossing technique were used in parallel electric and magnetic fields to investigate the Stark splitting of all the fine structure levels of the ground multiplet 4f ⁷ (⁸ S) 5d6s ^{2 9} D in Gd I. The tensor polarizabilities were deduced from the level crossing and the rf signals. The variation of the tensor polarizabilities is well reproduced by the LS coupling approximation, except for the small value of the⁹ D ₅ level. A value of the tensor polarizability of the 5d electron is evaluated from the experimental results, ₂(5d)=2.00(6) kHz(kV/cm)². It is shown that the ratio between the electric quadrupole constant and the tensor polarizability is constant, except for the⁹ D ₅ ratio, which is caused by a breakdown of the central field model.     

Radiative lifetimes of the Rb(n 2 F)(n=6, 7, 8) states measured with the stepwise dipole-quadrupole excitation scheme

We report measurements of lifetimes of the Rb(n ² F)(n=6, 7, 8) states performed in a vapour cell. TheF-states were excited in a two-step sequence of an electric-dipole transition followed by an electric-quadrupole transition. Single photon counting was used for detection. The results are: (6² F)=171(4), (7² F)=262(15), (8² F)=387(12) (in ns). These lifetimes, have been compared with theoretical values given by different authors. An estimate of the cross sections for quenching due to collisions with ground-state Rb atoms is also given.This work was supported by the Polish Committee for Scientific Research under grant No. 2 2341 92 03     

Hyperfine structure of the 33 P state of3He and isotope shift for the 23 S-33 P 0 transition

The hyperfine structure of the³He 1s 3p ³ P state and the³He-⁴He isotope shift is determined by high precision measurements of the 1s2s ³ S ₁-1s 3p ³ p ³ P _J transition frequencies near 389 nm. A direct frequency measurement is made without the need for wavelength calibration by tuning a single laser to the atomic frequency, and using a novel heterodyne method to observe beat frequencies with a stable reference laser. A fit to a theoretical model of hyperfine structure is used to determine the hyperfine shifts. Additional off-diagonal mixing effects are investigated to resolve a possible systematic discrepancy in the hyperfine intervals. The final isotope shift without hyperfine structure of 42184308±165 kHz is used to deduce an rms nuclear charge radius for³He of 1.956±0.042 fm. This is in good agreement with other values obtained from atomic isotope shift measurements, and a recent theoretical value of 1.958±0.006 fm. The present result helps to resolve substantial differences in the³He nuclear radius derived from electron-nuclear scattering measurements, and it provides a significant test of the nuclear three-body problem.     

Collisional broadening of Rydberg atoms perturbed by ground-state sodium atoms

Collisional broadening ofnS Rydberg states of alkali-metal atoms by sodium atoms is calculated using the adiabatic approach for the³ quasimolecular state, and impulse approximation for all other contributions to the collisional width. We obtain oscillatory dependence of the collisional width on the principal quantum number which was observed earlier for heavy alkalies as perturbers. However, the width and the amplitude of the oscillation are much lower than in the case of heavy alkalies. We present a comparison between the results for broadening of heavy alkalies by sodium and for broadening of sodium atoms by heavy alkalies.     

Isomerisation and phase transitions in small sodium clusters

Using a distance-dependent tight-binding hamiltonian, we have studied the influence of the temperature on the geometries of small alkali clusters (Na₄, Na₈, and Na₂₀). We have applied a Monte-Carlo thermodynamical method which consists in performing canonical samplings for various temperatures, these samplings being reexpressed in the microcanonical ensemble. This method provides thermodynamical values such as the entropy and the specific heat. Their behaviour shows one phase transition in the case of Na₄ and Na₈, and two phase transitions for Na₂₀. As concerns Na₄ and Na₈, the transition occurs at 200 K, between a solid-like phase and a phase for which the geometry of these clusters oscillates between numerous shapes. In the case of Na₂₀, the two observed phase transitions can be described as a melting of the surface atoms (at 200 K) preliminarily to the fluctuation of an inner icosahedron seed (at 300 K).     

Ionization potential measurements of hydrogenated lithium clusters

Ionization Potentials of Li_nH_m clusters have been measured by photoionization. As in Li_n, odd-even alternations and shell closing effects are observed. In a first approximation, we find that Li_nH clusters behave like Li_n–1 and Li_nH₂ like Li_n–2. The results may be interpreted by assuming that the bonding of one hydrogen localizes one electron and that the other electrons remain delocalized.     

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.