Exchange currents in electric transitions and the rôle of siegert's theorem: A case study in deuteron photodisintegration

The hyperfine structure (hfs) splittings of the metastable 1s2s ³ S ₁ state of⁷Li⁺ have been measured with combined laser optical pumping and microwave resonance. A lowenergy Li⁺ ion beam, optically excited by an intersecting laser beam, passed a waveguide where radio frequency transitions were induced. The resulting population transfer among the hfs levels of the³ S ₁ was detected via the change in intensity of the fluorescence light from a second crossing region of laser light and ion beam located past the waveguide. The magnetic hfs constantA(⁷Li⁺, 1s2s ³S₁) was measured and compared with theory. A deviation of the two transition frequenciesν(F=3/2?F=5/2) andν(F=1/2?F=3/2) from the interval rule is due to a depression of theF=3/2 hfs sublevel, caused by mixing of the 2³ S ₁ and 2¹ S ₀ states via hyperfine interaction. This shift was never observed so far in a two-electron spectrum, because of absence ofI>1/2 isotopes in He, the only two-electron atom investigated spectroscopically with high precision. The size of the shift is in fair agreement with a theoretical estimate.     

Twenty-parameter eigenfunctions and energy values of the 23 S States of He and He-like Ions

Twenty-parameter calculations of the energies and wave functions of the first excited states 2³ S of He, Li⁺, Be⁺⁺, B⁺⁺⁺, O⁶⁺, Ne⁸⁺, Mg¹⁰⁺, have been carried out using Hylleraas' method. The energy values have been corrected for mass polarization. The coefficients of the best wave functions are listed. Similar calculations for the 2³ S state of the H^? ion yield an energy value which cannot be distinguished from the energy of a free H atom. For He and Li⁺, in addition, forty-parameter calculations have been carried out. The results compare well with the recent calculations of Pekeris using a somewhat different method. Even after the inclusion of the relativistic correction, the theoretical energy values deviate slightly from the observed. The differences, ?0·10±0·05 cm^?1 for He and ?1·07±0·10 cm^?1 for Li⁺, represent observed values of the Lamb shifts in the 2³ S states. These values agree within their uncertainties with the values predicted from quantum electrodynamics.     

Triplet-singlet interaction in the 1s 2s3S1 hyperfine splitting of he-like Li+

The hyperfine structure (hfs) interaction between the metastable 2³ S ₁ and 2¹ S ₀ states in^{6, 7}Li⁺ causes very small equal and opposite energy level shifts,δ, in the two levels having the same total angular momentum quantum numberF=I. This amounts to 12ppm with respect to the total hfs splitting of 30 GHz for the⁷Li⁺ 2³S₁ state and has been measured for the first time directly for the case of a core-free electronic system by combined laser-microwave spectroscopy. A new calculation ofδ with accurate integral-transform 2¹ S ₀ and 2³S₁ wave functions is reported. Configuration interactions and electron exchange and correlation effects, which differ for parallel (³ S ₁) and antiparallel (¹ S ⁰) spins, are treated in detail in order to obtain very good agreement between measured and theoretical values for this tiny perturbation. A complete understanding ofδ is indispensable for extracting fundamental constants from two-electron spectroscopic data.     

Recent progress of glass and glass-ceramics as solid electrolytes for lithium secondary batteries

In recent years many new glass-based solid electrolytes with high Li⁺ conductivity have been developed. In the present paper, we review the preparation and characterization of Li₂S-based oxysulfide glasses and sulfide glass-ceramics on the basis of two strategies of enhancing Li⁺ conductivity: the utilization of “mixed-anion effect” by combining sulfide and oxide anions, and the precipitation of superionic metastable crystals by careful heat-treatment of glasses. The superior Li⁺ conducting solid electrolytes with the highest conductivity and the lowest activation energy for conduction have been achieved in the Li₂S–P₂S₅ glass-ceramics. The use of these glass-ceramic solid electrolytes leads to the development of a bulk-type all solid-state lithium secondary battery with excellent cycling performance.     

Relative photodissociation cross-section of NaCs molecule,using argon ion laser lines

Laser-induced photodissociation of NaCs molecule has been observed when a mixture of Na and Cs metal vapour in a glass cell was irradiated by most of the lines of an argon ion laser. The photodissociation results in the 3P state of Na atoms which is correlated with theF ¹Σ⁺ and G¹π molecular states of NaCs. Distribution of photofragments over fine structure components 3² P _3/2 and 3² P _1/2 of Na has been studied. The ratio of intensity ofD ₂ line (5890 Å) toD ₁ line (5896 Å) of Na varies from around 2 at 5145 Å to about 3.5 at 4579 Å. The relative photodissociation cross-section increases monotonically as the wave-length of laser light decreases from 5145 Å to 4579 Å. It is seen that the 4579 Å photon is about 200 times more effective than the 5145 Å photon in causing the photoreaction NaCs + (Ar⁺ photon) → Na*(3P) + Cs(6S).     

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.     

Solid solutions Li1+xV3O8 as cathodes for high rate secondary Li batteries

Following a preliminary investigation, Li/Li_1+xV₃O₈ cells have been examined. Using samples of low x content, up to 3 eq Li⁺ could be accepted both chemically and electrochemically by one mole of active material. Li⁺ is accomodated in the tetrahedral sites existing between the (V₃O₈)^(1+x)- layers. Li⁺ jumping from site to site is fast and permits high rate capabilities: at 10 mA/cm², 1.1 eq Li⁺ per mole could still be inserted. The structure does not show irreversible alterations upon extended lithiation, allowing long cycle lives to be achieved. Kinetic constraints limit the recovery of the full capacity of the first discharge at medium-high rates, but the second-discharge capacity declines slowly with cycle number.     

Crystalline-structure-dependent green and red upconversion emissions of Er-Yb-Li codoped TiO2

Crystalline structures and infrared-to-visible upconversion luminescence spectra have been investigated in 1 mol% Er³⁺, 10 mol% Yb³⁺ and 0-20 mol% Li⁺ codoped TiO₂ [1Er10Yb(0-20)Li:TiO₂] nanocrystals. The crystalline structures of 1Er10Yb(0-20)Li:TiO₂ were divided into three parts by the addition of Yb³⁺ and Li⁺. Both green and red upconversion emissions were observed from the ²H_11/2/⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 transitions of Er³⁺ in Er³⁺-Yb³⁺-Li⁺ codoped TiO₂, respectively. The green and red upconversion emissions of 1Er:TiO₂ were enhanced significantly by Yb³⁺ and Li⁺ codoping, in which the intensities of green and red emissions and the intensity ratio of green to red emissions (I_green/I_red) were highly dependent on the crystalline structures. The significant enhanced upconversion emissions resulted from the energy migration between Er³⁺ and Yb³⁺ as well as the distortion of crystal field symmetry of Er³⁺ caused by the dissolving of Li⁺ at lower Li⁺ codoping concentration and the phase transformation at higher Li⁺ concentration. It is concluded that codoping with ions of smaller ionic radius like Li⁺ can efficiently improve the upconversion emissions of Er³⁺ or other rare-earth ions doped luminsecence materials.     

CW ultraviolet saturation spectroscopy of the 6p 3P0-9s 3S1 transition in mercury at 246.5 nm

We have measured the even isotope structure of the 6p ³P₀-9s ³S₁ transition in mercury at 246.5 nm using saturated absorption spectroscopy with radiation produced as the sum frequency of a 363.8 nm argon ion laser and an LD700 ring dye laser in ADP. This is the first use of cw sum-frequency mixing in nonlinear laser spectroscopy in the ultraviolet. No previous cw Doppler-free measurements have been reported at wavelenghts below 294.5 nm     

NMR study of Li+-ion diffusion in the solid solution Li3+x(P1−x,Six)O4> with the γII-Li3PO4 structure

Diffusive motion of a Li⁺ ion in the solid solution of Li₃+x(P₁?x, Si_x)O₄ (0?x?0.4) with the γ_II-Li₃PO₄ structure was studied by the measurement of the ⁷Li spin-lattice relaxation time. The observed motion was a local motion instead of a long-range one. In comparison with the previous study on the solid solution of Li₄?x(P_x, Si₁?x)O₄ with the Li₄SiO₄ structure, it is noticeable that the activation energy is low and almost independent of the composition and that the attempt frequency is smaller in this phase. These characteristics were attributed to the availability of a large interstitial void in the γ_II-Li₃PO₄ structure. The low values of activation energy for the Li⁺ ionic conduction may be explained on the same basis.     

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.     

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.     

Hyperfine structure splitting of the positron-helium ions e +[3He(23 S)] and e +[4He(23 S)]

The hyperfine structure splittings are determined for the lowest bound state in the positron-helium ion e ⁺[³He(2³ S)] and e ⁺[⁴He(2³ S)]. In particular, it has been found that the three hyperfine structure splittings—5824.3986, 76 466.5308, and 5824.4019 MHz—can be observed for the e ⁺[³He(2³ S)] ion. In the e ⁺[⁴He(2³ S)] ion, only one hyperfine structure splitting 82963.0427 MHz can be observed. All these values can be measured in modern experiments.     

Two-photon intracavity dye laser spectroscopy of the 4S and 3D term in6, 7Li

Doppler-free two-photon spectroscopy of several states of^{6, 7}Li has been achieved by placing an atomic beam inside the dye laser cavity. The hyperfine structure splitting of the 4S state, the fine structure splitting of the 3D level as well as the isotope shifts of the 2S–4S and 2S-3D transition have been measured, by scanning the single-mode laser frequency and detecting the fluorescence light. In addition, signal detection by three-photon ionization via the resonant 3D state was accomplished.     

Isotope shift and hyperfine structure of43Ca by laser spectroscopy

The isotope shift⁴⁰Ca-⁴³Ca in the 4s ^{2 1} S ₀-4s4p ³ P ₁ intercombination line as well as the hyperfine structure splitting of the 4s4p ³ P ₁ state of⁴³Ca have been remeasured by saturation spectroscopy with a tunable stabilizedcw dye laser and an atomic beam of natural Ca as absorber. The nuclear charge radius of⁴³Ca obtained here reconciles our result with the radius obtained from measurements in muonic Ca-atoms and in the Ca resonance line. It reconfirms the fact that the charge radius of⁴³Ca is considerably smaller than the ones of both neighbouring even isotopes. The discrepancy of our previous measurement for this charge radius was due to a wrong assignment of so far unobserved absorption lines of probably molecular origin occuring in the neighbourhood of the atomic resonances under study.     

Laser transitions among the C1Πu, 31Σg+, A1Σu+, and X1Σg+ states of Na2

Intense infrared stimulated lines at wavelengths around 2.5 μm have been observed upon excitation of Na₂ by uv radiation from a frequency-doubled narrow-band dye laser. Frequencies of these IR lines have been measured when the pump laser was tuned to C¹Π_u ← X¹Σ_g⁺ assigned transitions in the wavelength range 331–334 nm. High-resolution spectroscopy measurements of the involved rovibrational levels of both C¹Π_u and 3¹Σ_g⁺ electronic states allow the unambiguous assignment of these IR laser lines to C¹Π_u → 3¹Σ_g⁺ transitions.     

Optical thermometry through green and red upconversion emissions in Er/Yb/Li:ZrO2 nanocrystals

Variations of fluorescence intensity ratio of green (generated from Er^{3+ 2}H_11/2 and ⁴S_3/2 levels) and red (generated from the sublevels of Er^{3+ 4}F_9/2 level) upconversion emissions in Er³⁺/Yb³⁺/Li⁺:ZrO₂ nanocrystals have been studied as a function of temperature under 976 nm laser diode excitation. In the temperature range of 323-673 K, the maximum sensitivities of about 0.0134 K^− 1 and 0.0104 K^− 1 are obtained by using green and red emission, respectively. Er³⁺/Yb³⁺/Li⁺:ZrO₂ nanocrystals show potential application value in nanoscale thermal sensor.     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Effect of Li-substitution on piezoelectric and ferroelectric properties of (Bi0.92Na0.92−xLix)0.5Ba0.06Sr0.02TiO3 lead-free ceramics

New lead-free ceramics (Bi_0.92Na_0.92−xLi_x)_0.5Ba_0.06Sr_0.02TiO₃ have been fabricated by a conventional ceramic technique and their electrical properties have been studied. X-ray diffraction studies reveal that Li⁺, Ba²⁺ and Sr²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ lattices to form a new solid solution with a pure perovskite structure. The partial substitution of Li⁺ for Na⁺ increases the remanent polarization P_r of the ceramics. Because of the large P_r and low coercive field E_c, the ceramics with x = 0.075–0.125 exhibit excellent piezoelectric properties: d₃₃ = 189–235 pC/N, k_p = 33.6–36.3% and k_t = 51.6–54.3%. The ceramics exhibit relaxor behaviors after the substitution of Li⁺ for Na⁺. Our results also suggest that polar and non-polar phases may coexist in the ceramics at temperatures above the depolarization temperature T_d.     

Determination of the lifetime of the mercury 63P1 state

A pulsed tunable dye laser was used for a high resolution experimental study of mercury fluorescence from the 6³P₁ state. The output of the dye laser was frequency doubled into the 253.7 nm region using a potassium penta-borate crystal. Exponential decays were observed for each of the five individual components of the hyperfine structure separately and the effects of the trapping of resonance radiation on the observed lifetime of the 6³P₁ state of mercury were investigated for each resolvable component. Within experimental error, the natural radiative lifetime of the 6³P₁ state was found to be independent of the hyperfine component irradiated and a value of 122±2 nsec was obtained, consistent with results found by other methods.