Isotope shifts and hyperfine structures investigation of doubly excited levels in SrI

We measured isotope shifts and hyperfine structure of visible transitions of stable strontium isotopes by means of Doppler-free saturated absorption spectroscopy. In particular, we investigated transitions between excited states where the upper level involves two excited electrons. We report hyperfine coupling constants for the levels 5p4d¹D₂, 5p4d³F₂, 5s4d³D₁, 5s6s³S₁, 5s5p³P₁ and, for some of the studied transitions, we separate the specific mass and volume contribution to the isotope shifts.     

Hyperfine structure measurements of the metastable (3d 6 4s 2)3 H 4, 5, 6 states of57Fe: Configuration interaction in the hyperfine structure of the iron atom

We report the hyperfine structure (hfs) measurement of the metastable (3d ⁶ 4s ²)a ³ H _{4, 5, 6} states of⁵⁷Fe. The kHz-precision of these experimental results together with the hyperfine structure values of (3d ⁶ 4s ²)a ⁵ D _{1, 2, 3, 4}, (3d ⁷ 4s)a ⁵ F _{2, 3, 4, 5}, and (3d ⁷ 4s)a ³ F _{2, 3, 4}, which were measured earlier, allowed to determine a very detailed set of effective radial parameters describing the hfs of these states, using a new parametrization method. This method treats one- and two-body contributions to the hfs separately. In this way configuration interaction effects in the hfs of the⁵⁷Fe atom can be studied in detail and compared with configuration interaction effects in the fine structure of the same atom.     

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.     

Collisional de-excitation of the metastableD-states of Ba+ by He,Ne, N2 and H2

The rate constants 〈σ · υ〉 for collisional de-excitation of the metastable 5D states of Ba⁺ ions have been determined in an ion trap experiment. TheD-states are selectively populated by pulsed laser excitation of the 6P _1/2 or 6P _3/2 state and the decay at different background pressures is monitored by the change in fluorescence intensity of the excited ions. From the pressure dependence of the decay constants we calculate the de-excitation rate constants for different collision partners, averaged over the velocity distribution of the trapped ion cloud. For He, Ne, H₂ and N₂ we obtain in the c.m. energy range of 0.1–0.5 eV: 〈σ·υ〉 (He)=3.0±0.2·10^?13cm³/s, 〈σ·υ〉 (Ne)=5.1±0.4·10^?13cm³/s, 〈σ·υ〉 (H₂)=3.7±0.3·10^?11cm³/s, 〈σ·υ〉 (N₂)=4.4±0.3·10^?11cm³/s. The results can be understood qualitatively by a consideration of the ion-atom and ion-molecules interaction potential.     

Hyperfine structure and isotope shift of some even parity levels in the YbI spectrum

Using laser induced fluorescence spectroscopy the hyperfine structure of the even parity levels 4f ¹⁴6s6d ³ D ₁, 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 as well as of the odd parity level 4f ¹⁴ 6s6p ³ P ₂ in neutral ytterbium has been investigated. The isotope shift of the transitions 4f ¹⁴6s6p ³ P ₀ → 4f ¹⁴ 6s6p ³ D ₁ and 4f ¹⁴ 6s6p ³ P ₂ → 4f ¹⁴ 6s8s ³ S ₁, 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 could be measured with high accuracy. The results for the 4f ¹⁴ 6s6p ³ D ₁ level show a considerable influence of second order effects of the hyperfine interaction. The isotope shifts of the 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1 levels indicate a possible configuration mixing for these levels.     

Natural radiative lifetimes in the2 S 1/2 and2 D 3/2, 5/2 sequences of neutral copper

Natural radiative lifetimes have been measured of the 3d ¹⁰ ns ² S _1/2 (n=6?10) and of the 3d ¹⁰ nd ² D _{3/2, 5/2} (n=5?9) sequences by using two step excitation of copper atoms in an atomic beam. The states investigated were populated by the light from two pulsed dye lasers pumped by the same Nd:YAG laser. The lifetimes of the² D sequence increase regularly with increasing principal quantum number. This is not the case for the² S series, because of configuration interaction in the² P series. In addition the lifetime of the 3d ¹⁰5p ² P _3/2 state has been measured together with its branching ratio.     

J and term dependences in the isotope shift of Eu I

High-resolution laser atomic beam spectroscopy has been applied to studyJ and term dependences in the isotope shift of the levels 4f ⁷5d6s a ¹⁰ D _J ,a ⁸ D _J of Eu I. A parametric analysis of the isotope shift has been performed. TheJ dependence is interpreted through two term-dependent parametersz _5d , and the term dependence through one parameterΔT:z _5d (a ¹⁰ D)=44.1 (2.6) MHz,z _5d (a ⁸ D)=55.9 (2.3) MHz,ΔT=408.5 (3.2) MHz. Ab initio Hartree-Fock and Dirac-Fock calculations have been made to interpret these parameters. Within the accuracy of the calculations the parameters can be attributed to field shift effects.     

Lifetime measurements and stark mixing of autoionizing Cu I-states

Using a combination of collisional and laser excitation the lifetimes of 17 autoionizing Cu I states in the configurations 3d ⁹ 4s 6s and 3d ⁹ 4s4d were measured. The lifetimes are in the range of 1–50 ps and depend strongly on the coupling properties, the mixing with different configurations, and the radial integrals of the discrete with the continuum states. For the level 3d ⁹ 4s 4d ⁴ S _3/2 the influence of an electric field via Stark mixing of 3d ⁹ 4s 5p ⁴ P _1/2 on the autoionizing rate was investigated. The experimental values are compared with theoretical results which follow from ab initio calculations for the transition probabilities and least square fit values deduced from the experimental positions. Good agreement is found only for theJ=3/2 levels of both configurations 3d ⁹ 4s 4d and 3d ⁹ 4s 6s.     

Photoelectron spectra and angular distribution in reson three-photon ionization of atomic iron: J dependence

Kenetic energies and angular distributions of photoelectrons emitted by three-photon ionization fo atomic iron through two-photon resonant state e⁷D_J and e⁵ D_J, were measured, by using visible lasers. J-resolved photoelectron bands attributab to the a⁶D_J and a⁴F_j ionic states are reported.     

Hyperfine structure in the configurations 4f 13 6s6p and 4f 125d6s 2 of TmI

The laser-atomic-beam spectroscopy has been used to make precise measurements of the hyperfine structure in transitions starting from metastable states of the configuration 4f ¹²5d6s ² in¹⁶⁹TmI. With the resulting experimental magnetic dipole hyperfine constantsA _J andA _J values from former investigations a parametric analysis of the hyperfine structure in the configurations 4f ¹³6s6p and 4f ¹²5d6s ² has been performed using wavefunctions from fine structure calculations. A comparison of theoretical and experimental hyperfine constants allowed a test of the reliability of the wave-functions used. The hyperfine parameters respectively hyperfine radial integrals determined from the analysis were compared with corresponding data from ab initio calculations for the ground configuration in TmI.     

Electronic structure and magnetic properties of TMRh12 clusters

We report an experimental study of energy pooling collisions involving Cs atoms in the 6P and 5D states. The 5D state was populated by a cw dye-laser tuned to the cesium dipole-forbidden transition 6S → 5D at 685.0 nm. The 6P state was populated by subsequent radiative relaxation of the 5D state. The 6P population density was determined from the absorption of a cw diode-laser probe beam. The population densities of the 5D state and the higher, by energy pooling excited states were determined by measuring the corresponding fluorescence intensities relative to the fluorescence intensity from the optically thin quasi-static wings of the cesium D ₂ line. The rate coefficient for the process Cs*(6P)+Cs*(6P)→Cs**(6D)+Cs(6S) is found to be (4.2±0.13)×10^?10 cm³ s^?1 at T=570 K. In addition, estimates of the rate coefficients for the processes Cs*(6P)+Cs*(5D)→Cs**(7D)+Cs(6S) and Cs*(5D)+ Cs*(5D)→Cs**(7F)+Cs(6S) are given.     

Isotope Shifts of Nitrogen around 800 nm

The Doppler-limited absorption spectra of ¹⁴N and ¹⁵N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets (3s⁴P_J→3p⁴D_J^o, 3s⁴P_J→3p⁴P_J^o, 3s²D_J→5s²P_J^o, and 3p²P_J^o→5s²D_J^o) were measured and their J-dependent specific mass shifts were observed and discussed.     

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.     

The collisional quenching of electronically excited arsenic atoms As(42DJ) and As(42PJ), studied by time-resolved attenuation of atomic resonance radiation

A kinetic investigation of electronically excited arsenic atoms in the low-lying states, As(4p^{3 2}D_J) and As(4p^{3 2}P_J), ca. 1.33 and 2.28 eV, respectively, above the 4⁴S_3/2 ground state, has been carried out by atomic absorption spectroscopy. Atoms in these optically metastable states were generated by the pulsed irradiation of suitable arsenic compounds (AsMe₃ for ²D and AsCl₃ for ²P) in different spectral regions and monitored photoelectrically by time-resolved attenuation of atomic resonance radiation. Rate constants for the deactivation of these two states are reported for a range of collision partners. The data are compared with those of the analogous states of lighter atoms in group V, namely, P(3²D_J, 3²P_J) and N(2²D_J, 2²P_J), and discussed in terms of spin and orbital symmetry considerations.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Hyperfine structure in 5s 4d 3 D —5snf transitions of87Sr

The hyperfine spectra of the 5s4d ³ D ₁-5s20f, 5s4d ³ D ₂-5s23f, and 5s 4d ³ D ₃-5s32f transitions of⁸⁷Sr (I=9/2) have been measured by collinear fast beam laser spectroscopy. The structure in the upper configurations is highly perturbed by fine structure splitting that is of comparable size to the hyperfine interaction energy. These perturbations can be adequately treated with conventional matrix diagonalization methods, using the 5s-electron magnetic dipole interaction terma _5s and the unperturbed fine structure splittings as input parameters. Additionally, hyperfine constants for the lower 5s4d ³ D configurations, including theA- andB-factors and a separation of the individuals- andd-electron contributions to these factors, are derived.     

Population and deactivation of lowest lying barium levels by collisions with He,Ar, Xe and Ba ground state atoms

Excitation transfer between the barium low lying excited states 6s6p ³ P ₁ ⁰ , 6s5d ¹ D ₂ and 6s5d ³ D _J by collisions with He,Ar,Xe and Ba has been investigated. The population densities in all levels involved were probed by absorption or by fluorescence usingcw lasers. The depopulation cross sections of the Ba³ P ₁ ⁰ state by collisions with noble gases were found to be σ_He(³ P ₁ ⁰ )=5.5·10^?16 cm², σ_Ar(³ P ₁ ⁰ )=4.6·10^?16 cm², and σ_Xe(³ P ₁ ⁰ )=1.7·10^?16 cm². For Ar, the collisional depopulation of the³ P ₁ ⁰ level is exclusively due to the transition to the¹ D ₂ state. Under the assumption that the³ D _J metastable states are populated collisionally by¹ D ₂ →³ D _J transfer only, we have deduced the upper limit for the corresponding cross section σ ₁₃ ^Ar =1.5·10^?18 cm². From the Ba¹ D ₂ and Ba³ D _J steady-state diffusion distributions, collisional relaxation rates of the¹ D ₂ and³ D _J levels were evaluated. The collisional relaxation rates by Ar and Ba yielded total cross sections for the depopulation of metastable levels: σ_Ar(¹ D ₂)=1.5·10^?17 cm², σ_Ba(¹ D ₂)?1·10^?13 cm², σ_Ar(³ D _J)=7·10^?21 cm², and σ_Ba(³ D _J)=1·10^?15 cm². Furthermore, it was found that the main contribution of the collisional depopulation of the¹ D ₂ state by Ar is related to back transfer to the³ P _J ⁰ state, whereas the deactivation of the³ D _J metastable state is due to back transfer to the¹ D ₂ state. Taking into account other cross sections reported in literature we can conclude that collisional deactivation of both metastable levels by Ba ground state atoms can be attributed to their mutual collisional mixing.     

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.     

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.     

Observation of the electric-field-inducedE1 transition between 5s4d 1 D 2 and 5s 2 1 S 0 levels in Sr I

The angular distribution of the electric-field-inducedE1 radiation is asymmetric with respect to the external electric field direction. Measurement of this asymmetry for the 5s4d ¹ D ₂ → 5s ^{2 1} S ₀ transition in strontium permits the experimental determination of the 5s5p ¹ P ₁ → 5s4d¹ D ₂ decay rate. The result is:A(¹ P ₁ →¹ D ₂)=(4.37±0.93±0.66) × 10³ s ^?1.