Hyperfine structure investigations of the tantalumI blend λ=6356.14 Å

The TaI line 6356.14 Å, up to now classified as the transition 5d ³6s ² a ⁴ P _5/2?5d ³6s(a ⁵ F)6p z ⁴ F ₇ ^2/0 , is a blend with a second transition, which is related to the additional levels 5d ⁴(b ³ G)6s a ⁴ G _9/2?39641.24 cm^?1 J=7/2°. Using laser excitation with optogalvanic and laser-induced fluorescence detection, the hyperfine constants of the four levels involved and the distance of the center wavelengths of the two fine structure transitions could be determined.     

Two-step laser optogalvanic spectroscopy of highJ momentum 4dnd and 4dng autoionizing states of strontium

We have measured the energies of about two hundred even parityJ=3–5 autoionizing 4dnd and 4dng Rydberg states of strontium (Sr) using an optogalvanic method. These states are reached by a two-step dye laser excitation from the 4d5s metastables through the 4d5p ³ P ₂,¹ F ₃,³ F ₄ intermediates. The 4d5s are populated in a d.c. glow discharge through a Sr heated cell. The electronic configuration of the observedJ=3, 4 states is deduced from the Lu-Fano plots of their quantum defect values and the spectral characteristics of the corresponding transitions.     

Lifetime measurements of the 3d 94s(1 D) 4p configuration of Cu I

The radiative lifetimes of the levels in the 3d ⁹4s(¹ D)4p configuration of Cu I are measured. The levels are excited from the metastable 3d ⁹4s ^{2 2} D _3/2,5/2 levels. The metastable Cu atoms are generated in a pulsed hollow cathode discharge. The levels investigated are populated with a 35-ps laser pulse at wavelengths around 220 nm. The laser induced fluorescence signal is detected. The lifetime of the 3d ⁹4s(³ D)4p ⁴ D _1/2 level is also determined by direct excitation from the ground state. A comparison with calculated literature values is given.     

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.     

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.     

Determination of radiative lifetimes in neutral nitrogen using short laser pulses from a distributed feedback dye laser

Radiative lifetimes were determined for two short-lived states in neutral nitrogen. Following photo-dissociation and two-photon excitation employing the same UV source, excitation to higher states was performed with a distributed feedback dye laser (DFDL). The lifetimes were found to be τ(2p ²4d ⁴ D _7/2)=17(3) ns and τ(2p ²5s ⁴ P _5/2)=22(3) ns.     

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.     

Two-photon absorption of dissociating TLI in strong laser fields

In a strong laser field (I=2 GW/cm²) TlI is dissociated by a two-photon process and the Tl fragment is detected state specifically. The yield of Tl 6p ² P _3/2 (Tl*) is measured as a function of the dissociation wavelength (480 nm–540 nm). If the dissociation wavelength is close to two-photon transitions of the Tl atom from 6p ² P _3/2 to np² P _1/2,3/2 or mf² F _5/2,7/2,n=10 ... 15,m=7 ... 12 dips in the yield are observed. These dips show a significant asymmetric broadening, compared to a free atomic transition and the observation is interpreted as an absorption process of the transient state of dissociating TlI during the laser pulse. By applying the Landau-Zener approximation for the potential crossing of dressed molecular states, we are able to describe the broadening and the power density dependence of the observations. Simulations show that the asymmetry is determined by the difference potential of the electronic states which are coupled by the laser field.     

Heterodyne laser spectroscopy of lithium ions: 23 P fine and hyperfine structure of7Li+

The fine structure (fs) splittings in the 1s2p ³ P _J=1,2,0 multiplet of the helium-like⁷Li⁺ ion were measured with a laser spectrometer. The results with 3σ errors are: Δv ₀₁ (³ P ₀,F=3/2?³ P ₁,F=5/2)=152081.6(2.0) MHz and Δv ₀₂ (³ P ₀,F=3/2?³ P ₂,F=7/2)=82704.3(1.9) MHz. Combining the new precise fs measurements with earlier hyperfine structure (hfs) results from laser-microwave spectroscopy provided improved fs constants:D ₁=?155709.0(2.1) MHz,D ₂=?93049.2(2.0) MHz, and hfs constants:A _c =3679.0(6) MHz,A ₀=51.0(4) MHz, andA _d =?11.3(1) MHz, thus allowing for a stringent test of available theoretical data. The spectroscopic method used in this work opens up the possibility of determining Li⁺, 2³ S?2³ P absolute transition frequencies with a precision of ～2·10^?9.     

Experimental and theoretical investigation of radiative lifetimes in neutral gallium

Using laser spectroscopic techniques the natural radiative lifetimes of 4s ² n ₁ s ² S and 4s ² n ₂ d ² D states of neutral gallium have been measured forn ₁ = 6 to 11 andn ₂ = 4 to 9. These states, as well as previously measured4s ² np ² P states, have been investigated theoretically using multi-configuration Hartree-Fock calculations. Oscillator strengths to all lower-lying states have been calculated and theoretical lifetimes of the investigated states evaluated. The² D sequence is strongly influenced by the 4s4p ^{2 2} D perturber, and strong cancellation effects in the radiative decay are observed both theoretically and experimentally.     

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.     

3dnl J=3e autoionizing levels of calcium: observation by laser optogalvanic spectroscopy and theoretical analysis

The even parityJ=3 autoionizing spectra of calcium were investigated below the 3d threshold by a two-step laser excitation from the 3d4s metastables through the 3d4p ³ P ₂,¹ F ₃ intermediate states. The 3d4s were populated by electronic collisions in a d.c. glow dis-charge through a Ca heat-pipe. More than a hundred resonance transitions have been measured with an accuracy of ～0.2 cm^?1 for the narrow ones using standard laser calibration techniques. Their upper levels are assigned to all expected nine autoionizing 3dns, 3dnd and 3dng Rydberg series and the 4p 5p ³ D ₃ perturber. The theoretical interpretation is achieved by a combination of the eigenchannelR-matrix and mulitchannel quantum defect (MQDT) methods. Ten closed and two openJ=3 interacting channesl are used. Theoretical energy level positions and excitation profiles are compared with the experimental data confirming the identification of the observed structures. Strong mixing between the 3d _3/2 nd _5/2 and 3d _5/2 nd _3/2 series is found, while the 3d _3/2 nd _3/2 and 3d _5/2 nd _5/2 series are almost purejj-coupled. The calculations were particularly successful in reproducing the spectrum in the region of the 4p 5p ³ D ₃ perturber, where strong chancel mixing appears leading to interference effects in the excitation cross sections.     

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.     

High resolution spectroscopy of iridium in a hollow cathode discharge

We demonstrate the possibility of performing high resolution laser spectroscopy of iridium atoms produced by sputtering in a hollow cathode discharge. By resolving the hyperfine structure of ultraviolet transitions from the ground state, we measure the magnetic dipole and electric quadrupole constants of the 5d ⁷ 6s 6p ⁶ G _11/2 and 5d ⁷ 6s 6p ⁶ F _7/2 excited levels and we obtain accurate values for the isotope shifts. Iridium is also discussed as possibly providing reference spectra in the 243 nm region, close to the wavelength of the 1s–2s two-photon transition of hydrogen.     

Laser and radio-frequency spectroscopy of the 5d 36s 2 4 P 3/2,5/2 states in Ta I

The hyperfine structure of the metastable atomic states 5d ³6s ^{2 4} P _3/2 and⁴ P _5/2 in¹⁸¹Ta has been studied using high resolution laser spectroscopy and laser radio-frequency double-resonance methods.     

On the line intensity ratios of prominent Si II,Si III,and Si IV multiplets

Line intensities of singly, doubly and triply ionized silicon (Si II, Si III, and Si IV, respectively) belonging to the prominent higher multiplets, are of interest in laboratory and astrophysical plasma diagnostics. We measured these line intensities in the emission spectra of pulsed helium discharge. The Si II line intensity ratios in the 3s3p²²D–3s²4p²P^o, 3s²3d²D–3s²4f²F^o, and 3s²4p²P^o–3s²4d²D transitions, the Si III line intensity ratios in the 3s3d³D–3s4p³P^o, 3s4p³P^o–3s4d³D, 3s4p³P^o–3s5s³S, 3s4s³S–3s4p³P^o, and 3s4f³F^o–3s5g³G transitions, and the Si IV line intensity ratios in the 4p²P^o–4d²D and 4p²P^o–5s²S transitions were obtained in a helium plasma at an electron temperature of about 17,000 ± 2000 K. Line shapes were recorded using a spectrograph and an ICCD camera as a highly-sensitive detection system. The silicon atoms were evaporated from a Pyrex discharge tube designed for the purpose. They represent impurities in the optically thin helium plasma at the silicon ionic wavelengths investigated. The line intensity ratios obtained were compared with those available in the literature, and with values calculated on the basis of available transition probabilities. The experimental data corresponded well with line intensity ratios calculated using the transition probabilities obtained from a Multi Configuration Hartree–Fock approximation for Si III and Si IV spectra. We recommend corrections of some Si II transition probabilities.     

Stark manifolds of barium Rydberg states

In a CW laser-atomic beam experiment Stark manifolds in barium originating from the Rydberg states 6s40f ¹ F ₃, 6s40g ^1,3 G ₄,³ G ₅ and 6s40h ^1,3 H ₅ have been studied. Accurate quantum defect values for higher orbital angular momentum states (l=6, 7) have been determined. The Stark manifolds are also calculated by diagonalization of the energy matrix in the presence of an external electric field. Good agreement between experiment and calculations is obtained.     

Lifetimes and perturbations of the 3d9 4s(3D) 4p structure in the spectrum of copper I

Natural radiative lifetimes have been measured of the²P,²D,²F and⁴D_5/2 terms in the 3 d⁹ 4s(³D) 4p structure of copper I. A pulsed hollow cathode was used to generate 3d⁹ 4s^{2 2}D metastable atoms. From these metastable levels the states investigated were populated by a pulsed dye laser pumped by a Nd:YAG laser. A comparison with theoretical and experimental literature values is given.     

Accurate time-resolved laser spectroscopy on sputtered metal atoms

The delayed coincidence photon counting technique, employing a picosecond tunable dye laser as an excitation source, has been used for accurate determinations of radiative lifetimes of excited states. Excitation from meta-stable states of sputtered atoms was employed. We obtained for Cu: τ(3d ¹⁰ 4p ² P _1/2 = 7.27(0.06) ns, τ(3d ¹⁰ 4p ² P _3/2) = 7.17(0.06) ns and for Fe: τ(3d ⁷ 4p y ³ F ₂)= 9.06(0.16) ns, τ(3d ⁷ 4p y ³ F ₃) = 9.06(0.13) ns and τ(3d ⁷ 4p y ³ F ₄) = 9.11 (0.16) ns. Also, the ability of this technique to record quantum beats at frequencies up to 1 GHz is demonstrated.