Multi-step laser excitation of the highly excited states of zinc

We report experimental data on the highly excited states of zinc in the energy range 74,625-75,740 cm⁻¹ using two-step laser excitation scheme in conjunction with a thermionic diode ion detector. The 4s4p ³P₁ inter-combination level at 32501.399 cm⁻¹ was populated using a frequency doubled dye laser. The 4s5s ³S₁ level at 53672.28 cm⁻¹ gets populated from the ASE (amplified spontaneous emission) of the second step dye laser. The Rydberg series 4snp ³P₂ (12 ? n ? 60), 4snp ¹P₁ (16 ? n ? 30) and parity forbidden transitions 4sns ³S₁ (19 ? n ? 44) have been observed. A two parameter fit to excitation energies of the observed series yields the binding energy of the 4s5s ³S₁ level as 22097.03 ± 0.03 cm⁻¹ and consequently, the first ionization potential of zinc is determined as 75769.31 ± 0.05 cm⁻¹, that is in excellent agreement with the earlier work.     

Impact broadening and shifts for 6sns 1S0 and 6snd 1D2 series of barium

Impact broadening and shifts of Ba transitions to parity forbidden Rydberg states have been measured using two-photon laser spectroscopy techniques. Broadening and shift rates for the 6sns ¹S₀ (10 < n < 19) and 6snd ¹D₂ (8 < n < 26) levels due to thermal collisional interactions with Xe, Kr and Ar as perturber gases are plotted. Perturbations due to configuration interactions are discussed.     

Two-photon spectroscopy of ytterbium

Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f¹⁴ 6sns¹S₀ and 4f¹⁴ 6snd ¹D₂ states are seen in direct two-photon excitation. Hybrid resonances involving 4f¹⁴ 6s6p ¹P⁰₁ and 4f¹⁴ 5d6s ³D₂ intermediate states lead to transitions to 4f¹⁴ 6sns¹S₀, 4f¹⁴ 6snp ³P⁰_2,1 and 4f¹⁴ 6snd ¹D₂ levels.     

High resolution photoelectron spectrometry of negative ions: Fine-structure transitions in O− and S− photodetachment

The energy spectra of electrons detached from O^? and S^? ions by 488.0 nm and 514.5 nm photons have been measured with high electron energy resolution (5 meV) in order to determine the branching ratios for the various² P _{3/2, 1/2} →³P_{2, 1, 0} fine-structure transitions together with their respective angular distributions. Detailed information on the relative importance of thes- andd-wave continuum is obtained.     

The role of the configuration interaction in excitation of the Cd(II) principal series at electron-atom collisions

The excitation functions of Cd(II) spectral lines, namely, the lines of the 4d ¹⁰5s ² S _1/2?4d ¹⁰ np ² P ₃ ^2/0 (n≤10) principal series and the line corresponding to a transition from the Beitler level 4d ⁹(5s5p ¹ P ⁰)² P ₃ ^2/0 , are analyzed under the conditions of electron-cadmium atom collisions in the electron energy range from excitation thresholds to 400 eV. It is found that the excitation functions of the spectral lines attributed to transitions from the Beitler level are similar to those of the principal series lines corresponding to transitions from the 4d ¹⁰ np ² P ₃ ^2/0 (n=9, 10) levels nearest to the Beitler level. This similarity is explained by the significant admixing of the Beitler level to the initial levels of the principal series lines. It is shown that the admixing substantially affects the excitation functions of this series for the states more distant from the Beitler level (up to n=6).     

Measurement of the lifetime of the3 P 2 and4 P 5/2 states in Ar16+ and Ar15+

Promptly decaying levels in Li- and Be-like Ar could be identified in the delayed x-ray and electron spectrum in addition to the four known metastable (1s2s)¹ S ₀, (1s2s)³ S ₁, (1s2p)³ P ₂, and (1s2s2p)⁴ P _5/2 states in He- and Li-like systems. The states having lifetimes of about 10^?14s still contribute to the spectrum observed 10^?9s after the ions have passed a foil. This observation is explained by cascading processes from states of high principal quantum numbern≧14. The measured lifetime of the⁴ P _5/2 state subtracting the contribution of cascades is (0.594±0.016) ns and slightly larger than the theoretically predicted value of 0.563 ns. The³ P ₂ state is depopulated at short distances behind the foil by cascading processes. Its measured lifetime of (1.44±0.08) ns compares to a theoretical value of 1.48 ns.     

Three-photon resonance enhanced excitation spectrum of atomic thallium

We present first measurements on the resonance enhanced three-photon excitation in thallium, using a Nd:YAG laser pumped dye laser in conjunction with a thermionic diode ion detector. The even-parity 6s²ns²S_1/2 (15 ? n ? 31) and nd ²D_5/2 (13 ? n ? 42) Rydberg states have been observed. The measured level energies reveal a dynamic shift from the photoabsorption values, which is decreasing with increasing n, while the asymmetry in the line profile is observed to be increasing with increasing n. In addition, an autoionising level (sp²⁴P_3/2) adjacent to the ionization threshold has been observed and quantitatively analyzed using the Fano’s photoionization cross-section relation for an isolated autoionising resonance.     

Infrared laser-emission study in a resonantly excited sodium vapor

We report on a study of time dependence of ir laser emission at 3.41 μm in a dense Na vapor that is resonantly excited to the 3² P levels by a flashlamp, pumped dye laser. Energy-pooling collisions (excitation transfer) between excited atoms create a large population inversion among the 5² S _1/2 and 4² P _3/2 states which is destroyed by electron collisions as a result of subsequent plasma formation. The ir laser emission may serve as a new diagnostic tool to follow the time evolution of such media.     

Observation of dielectronic satellites in the K-spectrum of argon ions in plasma produced by femtosecond laser pulses

The satellite structure of 1s2p ^1,3 P ₁-1s ²¹ S ₀ lines of the He-like argon ion in plasma produced by a 45-fs laser pulse in a gas-jet cluster target is measured with a high spectral resolution. Radiation transitions 2p → 1s from autoionizing states (AISs) are detected for ions ranging from Li-like to F-like. The spectrum observed is theoretically simulated with the use of the spectroscopic data for the AISs of multicharged ions obtained within the multiconfiguration relativistic Hartree-Fock method. Good agreement with experimental data is obtained when the main population channels of these states are taken into account for typical values of cluster-target plasma parameters.     

The controlled excitation of forbidden transitions in the two-photon spectrum of strontium by using collisions and electric fields

We present experimental results involving controlled configuration mixing in two-photon spectroscopy of highly-excited states by exploiting a weak external electric field and collisions. The method has allowed new extensions to high members of the two-photon forbidden J = 3 odd-parity 5snf ¹F₃ and the J = 0, even-parity 5sns ¹S₀ Rydberg series of neutral strontium to be observed. We achieve resonant two-photon transverse excitation of a high density atomic jet by using a narrow bandwidth tunable dye laser in a heat pipe setup with sensitive ionization detection. Experimental term values are extended for the 5sns ¹S₀ series up to n = 46. By suitable exploitation of the composition and pressure of the buffer gases in conjunction with the electric field strength in the excitation region and the exciting laser beam intensity we have also extended observations up to n = 44 for the 5snf ¹F₃ series and up to n = 46 for the 5snp ¹P₁ series. Our results demonstrate a novel and remarkably simple experimental method to access high Rydberg states to which transitions are forbidden from the ground state by parity and other selection rules.     

Fluorescence resolue dans le temps des niveax de singulet et d du zinc

The time resolved spectroscopy technique is applied to investigate the (4s, nd) ¹D₂ series of Zn I using a selective stepwise excitation via the resonant 4¹P₁ state. Radiative lifetimes of n¹S₀ (n = 6?8) and n¹D₂ (n = 4,5) levels are measured. Upper limits for transition probabilities 4¹P₁?n¹S₀ (n = 9?12) and 4¹P₁?n¹ (n = 6?10 ) are obtained. Strong configuration interaction effects are observed in the ¹D₂ series and compared with those in Mg I and Cd I.     

Intensity distribution of a capillary-discharge 46.9 nm soft X-ray laser

We realize a Ne-like Ar 46.9 nm soft X-ray laser pumped by a capillary discharge. The study of the laserpulse-intensity distribution is important for applications of soft X-ray lasers. The intensity distribution demonstrates the gain distribution, plasma radius, and axial plasma density that contribute to the study of the laser-pulse formation. To measure the intensity in different positions of the X-ray laser spot, we moved transversally an X-ray diode (XRD) assembled with a slit. We obtain the onedimensional intensity distribution. We find a laser divergence (FWHM) of 4.0 mrad. According to the gain-guided model, we calculate the intensity distribution. The measured divergence of 4.0 mrad roughly corresponds to a plasma radius a approximately equal to 230–250 μm and on-axis electron density n _e ≈ 8.0?10¹⁸ ?9.0?10¹⁸ cm ^?3. The results of calculations indicate that the divergence of the intensity distribution increases when the plasma radius decreases and the on-axis electron density increases.     

Mössbauer study of the hyperfine and magnetic properties of organo-di-iron electron reservoirs containing a polyaromatic bridging ligand

Organo di-iron electron reservoirs Fe(CP^*)₂(Ar) ⁿ⁺ withn=2, 1, 0, where Cp^* is C₅(CH₃)₅ and where Ar are the following bridges: biphenyl, dihydrophenanthrene, triphenylene, have been studied by Mössbauer spectroscopy in the solid state. Complexes withn=2, with 36e^? in the coordination spheres of the metals, exhibit the usual diamagnetic behaviour of 18e^?, Fe^II mono-iron systems. Complexes withn=1, 37e^?, are delocalized mixed valence (Fe^IIFe^I) with a spin 1/2; the magnetic hyperfine interaction, measured under an external field, shows equal delocalization of the 37^th e^? on the two iron centers and the two bridging carbon atoms of the biphenylene. Complexes withn=0, formally with 38e^?, have a practically temperature-independent quadrupole splitting, and isomer shift values which constrast with the expected behaviour of independent Fe^I, 19e^? centers. This indicates that the 37^th and 38^th electrons are mostly located on the polyaromatic bridge. Spectra obtained in an external field show a negligible magnetic hyperfine interaction and support this conclusion. In the case of biphenyl and dihydrophenanthrene bridges, this electron localization can be related to a strong intramolecular chemical coupling, evidenced by other spectroscopic and X-ray data [1].     

Formation of N2 C3Πu and B3Πg by dissociative recombination of Ar 2 + in Ar+N2 early afterglow

The hf pulse excited Ar + N₂ mixtures and early afterglow are investigated at total pressures from 266 to 1995 Pa using nitrogen of 0·05–0·5% concentration. The time-resolved intensity of Ar I atomic lines and N₂ (2nd pos., 1st pos. and 1st neg.) band systems exhibit an intense early afterglow (0·3 ms). Both the decay of electron densityn _e and that of molecular Ar ₂ ⁺ ions and enhancement of coefficient of dissociative recombination due to electron temperature decrease after the pulse lead to the formation of characteristic secondary maximum of Ar I spectral line and N₂ molecular band intensities in the momentt _m after cut-off the pulse. The values oft _m(B³_g)>t _m(C³_u)>t _m(Ar I) decrease with increasing total pressure and increase with growing concentration of N₂ in Ar. In the afterglow period the Ar ₂ ⁺ dissociatively recombine in 5p and 4p Ar states. As a result of radiative transitions the metastable Ar (³P_2,0) atoms are formed which consequently due to collisions with N₂ molecules create electronically excited N₂. With increasing nitrogen concentration this effect becomes less pronounced and at concentration of N₂ greater than 0·5% it is negligible.     

Spectral and luminescent properties of jet-cooled dinaphthofuran

The fluorescence and fluorescence excitation spectra of jet-cooled dinaphtho[2,1-b:1′,2′-d]furan (dinaphthofuran) molecules, as well as their complexation with inert gases Ar, Kr, and Xe, are studied. The indicatrices of the degree of polarization of fluorescence of dinaphthofuran molecules upon excitation of the electronic transitions S ₀?S ₁ and S ₀?S ₂ are calculated as functions of the intramolecular orientation of the transition dipole moments. The fluorescence polarization spectrum is measured under excitation within the rotational contour of the line of the purely electronic transition v ₀ ⁰ = 29 294 cm^?1. In contrast to complex planar molecules, the S ₀?S ₂ fluorescence excitation spectrum of dinaphthofuran is found to be continuous, with the Q branch of the rotational contour being absent. The fluorescence excitation spectra of van der Waals complexes of dinaphthofuran with inert gases exhibit multiplet lines, which is associated with the helical structure of the molecules studied.     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

The kinetics of helium atom level excitation

An analysis is performed of the mechanism responsible for excitation of the levels 2³S₁, 2¹S₀, 2³P₀₁₂, 2¹P₁ of He in a gas discharge with a tubular cathode of special construction. Using the experimentally determined electron kinetic characteristics, the populations of these levels are calculated with consideration of transitions between the levels. The calculated data are then compared with the results of optical measurements.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 46–54, May, 1973.     

An investigation of the energy exchange mechanisms involving the 23S metastable level in an RF helium plasma

The energy exchange mechanisms present in a pure helium and a helium-neon plasma were investigated using spectroscopic diagnostic techniques. The plasma was spatially resolved and only the volume element at the plasma centerline was considered in the energy- exchange analysis. The experiment was conducted with a constant total pressure of 0·7 torr, a fixed oscillator frequency of 4 MHz, and a constant input power of 1·8 kW. Emission line spectroscopy was used to determine the population densities of 16 levels in the n³S, n³P, and n³D series. Spatially resolved, self-absorption measurements of the 2³P-2³S transition were used to determine the 2³S metastable level number density. The electron number density of 3·3 × 10¹³ cm^-3 was determined from the spatially resolved H_β blue wing profile, and a lower bound excitation temperature of 8800 °K was determined from a Boltzmann plot of the spatially resolved lower bound levels of the excited helium. The addition of 10% and 20% by volume of neon gas caused a measurable decrease in the population densities of the lower bound levels of helium, while the electron number density and lower bound excitation temperature remained unchanged. Three energy exchange models (local thermal equilibrium, corona, and collisional- radiative) were examined, and the collisional-radiative model was found to best describe the excitation processes for the 2³S level. This model was also appropriate for describing the helium-neon plasma at this level.     

Measurement of Ar(I) and Ar(II) transition probabilities in LTE ARC plasmas

The transition probabilities of two Ar(I) lines and one Ar(II) line have been measured in emission on wall-stabilized argon arc plasmas (0·5×10⁵?p, Nm^-2?3×10⁵; 10,000?T, K?20,000; 10²²?N_e, m^-3?5×10²³) using the “method of best fit (MBF)”. The results (without line-wing correction) are for Ar(I) at 714·7 nm, A_nm=5·66×10⁵ s^-1±5%; for Ar(I) at 430·0 nm, A_nm=3·40×10⁵ s^-1±5%; for Ar(II) at 480·6 nm, A_nm=8·82×10⁷ s^-1±7%. These values were not influenced by deviations from LTE, which have been observed at electron number densities n_e?10²³ m^-3. The small uncertainties were achieved after careful corrections of different sources of error.     

Probabilities of radiative dipole transitions of parahelium in an electric field

Quadratic Stark corrections to the wave functions, matrix elements, and probabilities of transitions between the singlet states ¹ S ₀ and ¹ P ₁ of helium atoms are calculated. The coefficients of the polynomials that depend on the effective principal quantum number of the upper level v _f and that approximate the numerical values of the polarizabilities, the quadratic corrections to the wave functions, and the probabilities of transitions to highly excited Rydberg states with large v _f are determined. The results of calculations testify that the probabilities of all σ transitions n _i ¹ S ₀ → n _f ¹ P ₁ and π transitions to the states with n _f > n _i /2 are decreased with increasing electric field strength, except for the transition 2¹ S ₀ → 2¹ P ₁, whose probability increases both for σ and for π transitions.