Resonances at collisions of slow electrons with cadmium atoms and ions

Using the crossed-beam method and a hypocycloidal electron spectrometer, the energy dependence of the ionization cross section for the cadmium atom has been studied in the near-threshold region and the elastic scattering of slow electrons at an angle close to 180° by Cd⁺ ions was studied for the first time. Within the region under study (0–7 eV above the first atomic ionization potential), a resonance structure determined by the contribution of atomic autoionization states is revealed in both the ionization curve and differential cross section of elastic scattering. The structure in the measured curves has been analyzed with the use of data on the ejected-electron spectra obtained under the excitation of autoionization states of Cd atoms, as well as the data on the optical excitation functions for the atomic spectral lines at λ=430.7 nm (5¹ P ₁-8¹ S ₀), 515.5 nm (5¹ P ₁-7¹ S ₀), 298.0 nm (5³ P ₂-6³ D _j ), and 361.0 nm (5³ P ₂-5³ D _j ).     

Precision measurements of optical excitation functions for zinc atom

The excitation of zinc atoms by ultramonoenergetic electrons is experimentally studied. The optical excitation functions for 19 atomic spectral lines that originate from the n ¹ S ₀, 4¹ P ₁, n ¹ D ₂, n ³ S ₁, 4³ P ₁, 6³ P ₂, and n ³ D _j levels are studied in detail. In the excitation functions measured from the excitation threshold to 19 eV for the spectral lines originating from the n ¹ S ₀, n ³ S ₁, n ¹ D ², and n ³ D _j levels, specific features caused by postcollision interactions of emitted and scattered electrons are observed for the first time in the energy region of 10.9–17.0 eV near the thresholds of autoionization states.     

Precision measurements of optical excitation functions for the cadmium atom

An experimental setup and a technique for the investigation of excitation of atoms by ultramonoenergetic electrons are described. The optical excitation functions are given for 14 spectral lines of the cadmium atom originating from the n ¹ S ₀, 5¹ P ₁, n ³ S ₁, 5³ P ₁, and n ³ D _j levels. More than 150 specific features are found in the energy dependences of the effective excitation cross sections measured from the excitation threshold to 16 eV. The most pronounced of these features are in good agreement with the fine structure observed previously. The main mechanisms of the initial-level population, namely, the direct transition of an electron from the ground atomic state to the initial level of a spectral line, the population of the initial levels due to the decay of short-lived states of a negative ion, and the cascade population, are separated. In the excitation functions of the lines originating from the n ¹ S ₀ levels, in the energy range from 10.9 to 12.4 eV, we observed for the first time an effect of postcollision interactions of emitted and scattered electrons in the vicinity of the thresholds of four autoionization states of the cadmium atom.     

Precision measurements of optical excitation functions for the mercury atom

We describe a computer-based facility for studying the excitation of atoms by ultramonochromatic electrons and give optical excitation functions for the 12 mercury spectral lines that originate from the n ¹ S ₀, n ¹ P ₁, n ¹ D ₂, n ³ S ₁, n ³ P _j , and n ³ D _j levels. We detected about 100 features in the energy dependences measured from the excitation threshold to 15.5 eV. The previously found positions of the features on the energy scale are in good agreement with our results. Most of the resonant features are shown to be mainly attributable to the decay of short-lived states of the negative mercury ion. We detected a postcollision interaction effect in the optical excitation functions of the lines that originate from the n ¹ S ₀ levels at energies of about 11 eV.     

Postcollision interaction upon electron excitation of the 5sns 1 S 0 and 5snd 3 D j levels of the cadmium atom

The optical excitation functions (OEFs) for two series of spectral lines of the Cd atom originating from the 5sns ¹ S ₀ (n = 6?11) and 5snd ³ D _{1, 2, 3} (n = 5 and 6) levels excited by an ultramonoenergetic (ΔE _1/2 < 0.05 eV) electron beam with energies exceeding the single ionization threshold are presented. In the energy range from 10.8 to 12.9 eV, the energy dependences of the excitation cross sections of the studied spectral transitions exhibit the effect of postcollision interaction of slow scattered and fast emitted electrons. This process leads to an additional population of the initial levels of the spectral transitions due to the capture of a scattered electron into an excited atomic level. The energies and widths of the electronic decay of autoionizing states are estimated in the classical approach by two methods, namely, by the least squares method and by direct calculation. Calculations are performed using approximate formulas valid for different relations between the postcollision shifts of the OEF maxima and the binding energies of the atomic levels. The terms of the autoionizing atomic states responsible for the maxima observed in the OEFs of the spectral transitions are determined.     

Lifetimes and oscillator strengths in the triplet system of ZnI

Selective laser excitation was used to measure the radiative lifetimes of the ZnI triplet states 4sns ³ S ₁(n=5–7) and 4snd ³ D ₃,³ D ₂ and³ D ₁(n=4–6). These states were excited from the metastable 4s4p ³ P states, which were collisionally populated in an atomic beam. The values are compared with the results of other experimental methods (beam-foil, pulsed electron excitation, Hanle effect) and with theoretical calculations. The corresponding oscillator strengths are discussed with respect to the astrophysical determination of the Zn photospheric abundance.     

The effect of the electric field on the spectral line shape

The effect of the external electric field on the spectral line shape under conditions of a uniform population of magnetic sublevels is studied in the density matrix formalism. The line shapes of spontaneous radiation for the atomic 4¹P₁-2¹S₀, 4³D₁-2³P₀, 4³S₁-2³P₀, 4³P₁-2³S₁, 4³D₁-2³P₁, and 4³S₁-2³P₁ transitions ofHe are calculated. The electric field is shown to be responsible for the spectral line shape asymmetry. Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 23–28, November, 1999.     

Slow-electron excitation of 3 S, 3 P, and 3 P 0 levels of the strontium atom

The electron impact excitation of ³ S, ³ P, and ³ P ⁰ levels of atomic strontium was investigated by the methods of extended crossed beams and optical spectroscopy. The results obtained are compared with the data of the previous experiment and the theoretical results. The behavior of excitation cross sections in spectral series of SrI is discussed.     

Stark interaction for excited states in alkali atoms,investigated by laser spectroscopy

The scalar polarizability constantα ₀ for excitedS- andD-states in rubidium and cesium was measured utilizing a two-step excitation scheme. An rf lamp and a single-mode dye laser were used to excite the atoms in a collimated atomic beam. Values ofα ₀ were determined for the 9–10² S _1/2 and 7–8² D _3/2 states of rubidium and for the 10–13² S _1/2, 9–10² D _3/2 and 9–11² D _5/2 states of cesium. Further, the isotope shift was evaluated in the 5579 Å rubidium line. A review of experimental polarizability constants for rubidium and cesium is given, and the results are compared with theoretical values.     

Approximation of the electron excitation cross sections for triplet states excited from the 23 S 1 metastable state in helium

The method of approximated four-parameter representation of the electron-impact cross sections for a helium atom excited from the 2³ S ₁ metastable state into higher triplet states is applied and discussed. The approximation consists in interpolation over the whole set of the cross section values for each helium atomic level measured in our experiments and reported by other researchers. The approximation parameters and the cross sections calculated using these parameters for the maxima of the corresponding excitation functions are presented for 19 triplet levels of the S, P, and D HeI series with n=2–10. The interpolated values are compared to the theoretical cross sections. The serial regularities were investigated for the S, P, and D levels studied and a decrease in the cross sections for excitation from the given metastable state within each series, described by the approximate law Q=Cn ^?5, was revealed. Validity of the similarity relationship and the Bethe approximation for cross sections in the 2³ S?n ³ P series was verified. It is shown that the cross sections for a triplet level excitation from the 2³ S ₁ metastable state exceed the corresponding values for excitation from the ground state of helium by a factor of approximately 10³ for n=2 and 3 and 10 2 for the higher levels. It is concluded that the proposed method of representation of the cross sections for the electron-impact excitation of triplet levels from the metastable state increases accuracy and more importantly, reliability of the final results.     

Effect of annealing and Mn doping on the photoluminescence of strontium tartrate crystals

Strontium tartrate crystals (STC) were grown in gel using the single tube diffusion method. Powder XRD and FTIR spectroscopy were used for the characterization of the crystal. The optical band-gap (Eg) of STC is found to be 5.46 eV. Photoluminescence (PL) spectra of STC are recorded at different annealing temperature and concentration of dopant Mn. The spectral peaks (λ_em) of strontium tartrate photoluminor lie around 417, 440, 513 and 620 nm with excitation wavelength (λ_exc)=379 nm. The peaks at 417, 513 and 620 nm correspond to transitions ²P_1/2⁰→²S_1/2, ¹D⁰→³P⁰ and ¹S→³P⁰, respectively of Sr. The PL peak observed around 440 nm corresponds to the a⁴D_7/2→a⁶S_5/2 transition of Mn.     

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).     

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.     

Excitation of doublet <Emphasis Type="Italic">D</Emphasis>-levels of a lutetium atom by electron impact

The electron-impact excitation of doublet D-levels of the lutetium atom is studied by the method of extended crossing beams. At the exciting electron energy of 50 eV, 64 excitation cross sections are measured. In the electron energy range of 0–250 eV, nine excitation optical functions are recorded. The occurrence of perturbations in the spectral series 6s ²(¹ S)6p ² P ₁^2/○ − 6s ²(¹ S)nd ² D _3/2 is discussed.     

Three-nucleon calculations without the explicit use of two-body potentials

Using as two-nucleon interaction input the ³S₁-³D₁ and ¹S₀ partial waves, the Faddeev equations are solved for the three-nucleon bound state. The ³S₁³D₁T-matrix is calculated from the Reid potential. Avoiding the usual potential fit, the ¹S₀T-matrix is directly continued off-shell and is constructed consistent with the ¹S₀ phase shift of elastic two-nucleon scattering. The off-shell part of the ¹S₀T-matrix is parametrized and with this parametrization the dependence of the three-nucleon bound-state properties is studied. As a result it is found that the binding energy varies only between 6.2 MeV and 6.8 MeV, while the minimum in the charge form factor for electron scattering from ³He lies between 12.9 fm^?2 and 18.7 fm^?2. The larger (smaller) ³He binding energy is accompanied by a ³He charge form factor whose minimum is at larger (smaller) momentum transfers.     

Investigation of highly excited states of calcium by three-photon ionization

The three-photon ionization in Ca from S₀ ground state is studied. The two-photon process is a near -- resonance process with one of the following bound states: 4s4d ¹D₂, 4p P₂, 4s6s ¹S₀, 4 D₂ and 4 S₀ while the third photon reach either directly the continuum or one of the autoionizing states. The succession of bound states as well as the transitions above the ionization limit are discussed. The dynamics of the multiphoton excitation processes is also discussed and radiative decay of 4 S₀ Ca state with two-photon excitation as well as (the measured) decay times of the Ca autoionizing states using the proper line profiles for different quantum numbers has been determined.Received: 29 September 2003, Published online: 18 May 2004PACS: 32.70.-n Intensities and shapes of atomic spectral lines - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Fb Photoionization of atoms and ions - 32.80.Rm Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)     

Second-order quadrupole splittings of the95Mo NMR signal in Mo(CO)6 and their reduction by sample spinning

The lifetimes of higher lying¹S_0?,¹D_2?, and¹F ₃ ⁰ -levels and of the 5s 7s³S₁- and 5p^{2 3}P₁-state in the Sr I-spectrum have been measured by a time resolved registration of the fluorescent intensity. The¹S_0? and¹D₂-levels were populated selectively by a two step optical excitation using two pulsed dye lasers. In the case of the¹F ₃ ⁰ -levels and of the³S_1?,³P₁-states the first excitation step was performed by a discharge, for the second, selective step a pulsed dye laser was used. The agreement of the experimental results with theoretically obtained lifetimes is satisfactory only in some cases.     

Neutron proton interaction potentials from experimental phase shifts

As an application of the inverse scattering technique of Marchenko, the single channelnp potentials¹ P ₁,³ P ₁,³ D ₂,³ P ₀ and¹ D ₂ are generated. Phase shift analyses below 1 GeV of Virginia serve as input. In these analyses, the³P₀ and the¹D₂ channels contain inelasticities above pion threshold. This work makes the first application of Marchenko's technique to higher partial waves and to nonunitary scattering functions.     

Two-photon excitation of Na atoms in a flame by broad-band laser irradiation

With a flashlamp-pumped tunable dye laser the 3S→3D, 3S→4D and 3S→5S two-photon transitions of sodium are excited and the resulting fluorescence radiation at various atomic transitions is detected. The sodium is nebulized into a stoichiometric H₂-O₂-Ar flame at atmospheric pressure and at a temperature of 1800 K. Collisional population exchange between several of the higher Na-levels is found to occur. Saturation and saturation broadening of two-photon transitions are observed. Formulas for two- photon excitation rates in the case of broad-band excitation are derived and show substantial agreement with experiment.