Laser cooling of a potassium�Cargon gas mixture using collisional redistribution of radiation

We study laser cooling of atomic gases by collisional redistribution, a technique applicable to ultradense atomic ensembles at a pressure of a few hundred bars. Frequent collisions of an optically active atom with a buffer gas shift atoms into resonance with a far red detuned laser beam, while spontaneous decay occurs close to the unperturbed resonance frequency. In such an excitation cycle, a kinetic energy of the order of the thermal energy k _B T is extracted from the sample. Here we report of recent experiments investigating the cooling of a potassium?Cargon gas mixture, which compared to a rubidium?Cargon mixture investigated in earlier experiments has a smaller fine structure of the optically active alkali atoms. We observe a relative cooling of the potassium?Cargon gas mixture by 120?K.     

An appraisal of the molecular model for the vk centre

The V_k centre in halide crystals is often described in terms of an X₂^? molecule ion. Recent molecular calculations for the halogen molecule negative ions have enabled a detailed comparison to be made between the theoretical anion and the results from optical and spin resonance studies on the crystals. The optical absorption line widths are naturally dependant on the host lattice, but the excitation energies and spin resonance constants may be readily interpreted in terms of the molecule. Certain anomalies in the spin resonance data for the heteronuclear defects, in particular ClI^? and BrI^?, show that the simple wavefunction constructed from “s” and “p” atomic orbitals does not adequately describe the polarisation of the large halogen atoms, and a more flexible wavefunction will be needed to calculate the spin resonance constants for these ions.     

Evaluating emission widths of giant dipole resonances in a Fermi liquid model

It is shown in the theory of finite Fermi systems that giant resonances can be considered as zero-sound excitations in concrete nuclei. Solutions to the zero-sound dispersion equation in symmetric nuclear matter, ωs(k), are obtained. Hydrodynamic models determine the wave vector k _A corresponding to giant resonance in a nucleus with atomic number A. The real and imaginary parts of ωs(k _A ) compare to the energy and escape width of giant resonance. Calculations are performed for giant dipole resonances.     

Heavy atom effect on photophysical deactivation of molecular triplet states

The decrease in the spin-orbit (SO) interaction with increasing number of chlorine atoms in molecules of dibenzo-p-dioxine derivatives is found and explained. The heavy atom effect on components of the rate constant of phosphorescence k _ph=_{k SO}+_{k VSO} related to SO and vibronic-spin-orbit (VSO) interactions is quantitatively estimated.     

Role of metastable atoms and molecules of helium in excitation transfer to hydrogen atoms

The afterglow of a discharge in helium with a small admixture of hydrogen is studied spectroscopically (p=40 Torr, [e]≤10¹¹ cm^?3). The time-resolved measurements of intensities of the first four lines of the Balmer series are performed. The concentrations of metastable helium atoms and molecules are evaluated from the relative intensity of the absorption lines. The ratios of excitation transfer rates from atoms He(2 ³ S ₁) k ₁(n) and molecules of helium He₂(a 2sσ ³Σ _u ⁺ ) k ₂(n) to atomic hydrogen H*(n) are measured to be k ₁(n=3)/k ₂(n=3)=0.04±0.02 and k ₁(n=4)/k ₂(n=4)=0.01±0.02. The ratios of excitation rate constants k ₂(n) corresponding to different states H(n) are measured to be k ₁(n=4)/k ₂(n=3)=0.023±0.01; k ₁(n=5)/k ₂(n=3)≤0.013; and k ₁(n=6)/k ₂(n=3)≤0.007.     

The gamma decay of high spin states of39K

First will be exhibited, for the stationary case, a connection between the probability, to find a particle in the region of interaction, and the derivative of the scattering phase shift for the momentum. From the idea, that in stationary scattering a resonance is linked with an appreciable increase of this probability, one obtains new and quantitative criteria for the behavior ofδ _l(k). For instance, the nonresonant behavior can be characterised by the condition 2k dδ _l(k)/dk<1. The maximum of probability for the particle to be in the region of interaction, is considered in accordance with the criterium of maximal change of the phase shift, as a function ofk. This characterises the location of the resonance. Wigner's lower limit fordδ _l (k)/dk allows to formulate a resonance condition directly for the cross section. Furthermore will be discussed some connections with the pole approximations of theS-matrix and the “collision lifetime” of Smith.     

X-ray absorption and emission spectroscopy at the Hf L1 edge of hafnium-(silicon)-oxide ultra-thin films

X-ray absorption and emission spectroscopic study at the Hf L₁ edge was applied to investigate the local structure around hafnium atoms in Hf(Si)O_x ultra-thin films, which are the most promising candidates for the high-k gate dielectric material of next generation CMOS devices. HfSiO_x showed an extra absorption above the Hf-L₁ threshold, which is not seen in HfO_x. HfSiO_x also had stronger Compton scattering peak in Hf-Lγ emission region, and smaller Hf-Lγ₂/Lγ₃ ratio, compared with those of HfO_x. These differences should be caused by partial replacements of hafnium atoms by silicon atoms as the second nearest neighbors of a hafnium atom.     

Calculation of the wave functions of the ground and weakly excited states of helium II

The wave functions of the ground (Ψ₀) and the first excited (Ψ_k) states of He II in the second-order approximation, i.e., up to the first two corrections to the corresponding solutions for a weakly nonideal Bose gas, are determined by the collective variable method, which was proposed by Bogolyubov and Zubarev and developed in the studies by Yukhnovskii and Vakarchuk. The functions Ψ₀ and Ψ_k = ψ_kΨ₀ are determined as the eigenfunctions of the N-particle Schrödinger equation from a system of coupled equations for Ψ₀, Ψ_k, and the quasiparticle spectrum E(k) of helium II. The results consist in the following: (1) these equations are solved numerically for a higher order approximation compared with those investigated earlier (the first-order approximation), and (2) Ψ₀ and ψ_k are derived from a model potential of interaction between He⁴ atoms (rather than from the structure factor as earlier) in which the potential barrier is joined with the attractive potential found from experiment. The height V ₀ of the potential barrier is a free parameter. Except for V ₀, the model does not have any free parameters or functions. The calculated values of the structure factor, the ground-state energy E ₀, and the quasiparticle spectrum E(k) of He II are in agreement with the experimental values for V ₀ ≈ 100 K. The second-order correction to the logarithm of Ψ₀ significantly affects the value of E ₀ and provides the asymptotics E(k → 0) = ck, while the second-order correction to ψ_k slightly affects the E(k). The second-order corrections to Ψ₀ and ψ_k have a smaller effect on the results compared with the first-order corrections, whereby the theory is in agreement with experiment; therefore, one may assume that the truncated Ψ₀ and ψ_k well describe the microstructure of He II. Thus, the series for Ψ₀ and Ψ_k can be truncated in spite of the fact that the expansion parameter is not very small (～1/2).     

On the determination of the unperturbed energy levels and the interaction matrix elements leading to a complex vibronic analogue of the Fermi resonance

A noniterative solution to the problem of determination of the unperturbed energy levels a _i and interaction matrix elements b _i describing a complex vibronic analogue of the Fermi resonance (the number of interacting states n > 2) is found. It is assumed that a _i and b _i can be determined on the basis of experimental data known for the resonance region, namely, the transition energies e _k and intensities I _k . The source of the intensity of observed transitions is assumed to be only one perturbed transition (the S ₀ → S ₂ transition of the 0-0 type or its vibronic sideband). The algorithm uses algebraic methods based on finding eigenvectors of real matrices of a particular form, whose elements are constructed from combinations of e _k and I _k .     

Anomalous dependence of the magnetic resonance signal of cesium atoms in the afterglow in an N<Subscript>2</Subscript>-Ar mixture

The investigation of spin-exchange collisions between optically oriented cesium atoms in the ground ² S _1/2 state and nitrogen atoms in the ground ⁴ S _3/2 state reveals an anomalous behavior of the magnetic resonance signal of cesium atoms in the afterglow in an N₂-Ar mixture, namely, the magnetic resonance signal is slowly enhanced during the time interval between the high-frequency pulses exciting a discharge in the absorption cell. It is found that such a behavior of the magnetic resonance signal is explained by a slow change in the concentration of nitrogen atoms in the absorption cell, which affects the magnetic resonance of cesium atoms via efficient spin exchange.     

An ESCA investigation of some dithiooxalato complexes

A series of dithiooxalato complex ions have been investigated as their tetraphenyl-phosphonium and potassium salts. Core-electron binding energies (E_b) of S, C, and O were determined, as well as those of the metals. From the first-mentioned data, effective charge values (q) were estimated for the atoms of the ligands. For this purpose linear relations (E_b = k · q + E_bO) were used that had been previously derived within a scheme using C ls (phenyl) as the internal standard. From the data thus obtained the effective charge on the metal atoms could be estimated. The data is used to test if analogous linear relations also hold for the heavy elements; for example, we have found E_b(Pt) = 3.17 · q_pt + 71.1 eV.     

The determination of theK-shell fluorescence yield of xenon by use of the proportional counter method

The wall-less proportional counter filled with propane with a small admixture of xenon was used as a spectrometer of electrons emitted by xenon atoms when photoelectrically excited by americium-241γ-rays and erbiumKα rays. TheK-shell fluorescence yield of xenon as extracted from spectra ammounts toω _k=0.889(1±0.01).     

Multidimensional elastic waves excited by oscillating domain walls

Magnetoelastic excitations with a fine structure in the 50kHz range have been observed in the study of the domain wall resonance (DWR) in magnetic garnet thin films. DWR excites standing transverse elastic waves which have a resonance frequency given by $\text{f=}\text{nv}\text{2d}$, where f is the frequency, n is an integer, v=3.5×10⁵ cm/sec is the transversal velocity of the elastic wave, and d=0.05 cm is thickness of the film/substrate system. A fine structure associated with each of these modes has been identified as due to two dimensional bulk elastic waves by using a set of parallel microstrip lines. The dispersion relation of these elastic waves is ω²=v²(k²₁+k²₂), where ω is the radial frequency, k₁ and k₂ are the wave vectors in the orientation perpendicular and parallel to the sample surface respectively. In the case of k₁?k₂, $\text{f=}\text{f}{}_0\text{+v}{}^2\text{k}{}^2{}_2\text{f}{}_0$, where f₀ is the resonance when k₂=0. The experimental results are in excellent agreement with this model. A linear dispersion, observed when using a shorted slot-line structure, is understood as the excitation of three dimensional modes due to the complex structure of the slot-line and the sample geometry.     

Soft X-ray photoemission study of nitrogen diffusion in TiN/HfO:N gate stacks

The impact of HfO:N post nitridation anneal (PNA) and gate fabrication on the physico-chemical properties of the TiN/HfO:N/SiO₂/Si stack are investigated using Soft X-ray Photoelectron Spectroscopy (S-XPS) and Vacuum UltraViolet Spectroscopic Ellipsometry (VUV-SE). Defects created in the high-k during plasma nitridation are passivated by PNA under O₂. Both oxygen and nitrogen diffusion is observed towards the bottom SiO₂/Si interface together with a regrowth of the SiO₂. These defects play a major role regarding nitrogen diffusion during gate fabrication. Without PNA, no diffusion is observed because O and N atoms are trapped inside the high-k. With PNA and simultaneous defects passivation, nitrogen from both metal gate and high-k diffuses towards the bottom SiO₂/Si interface.     

An X-ray photoelectron spectroscopy study of volatile tin compounds

Core-level X-ray photoelectron spectra of fifteen compounds of tin have been measured in the gas phase. The compounds include various organo and halo compounds as well as tin(IV) nitrate and Sn{N[Si(CH₃)₃]₂}₂. The tin binding energies span a range of 4.4 eV and are well correlated by the “transition-state” point-charge potential model equation using atomic charges calculated by the CHELEQ electro-negativity equalization method. As expected, the empirically determined parameter k for tin is smaller than the k values obtained in previous work for carbon, silicon, and germanium. For Sn(NO₃)₄, and Sn{N[Si(CH₃)₃]₂}₂, the bonding can be described as a weighted average of several resonance structures. In these cases the binding energy data were used in conjunction with the CHELEQ method to determine the resonance structure weightings.     

Mössbauer study of Nd2Fe14B and Nd2(Fe1−xCox)14B compounds

The Mössbauer spectra of Nd₂Fe₁₄B and Nd₂(Fe_1?xCo_x)₁₄B compounds (x=0.0.05, 0.10 and 0.16) have been investigated at room temperature and at 77 K. Taking advantage of combined ME and NMR investigations of the Nd₂Fe₁₄B compund, the hyperfine field values and their assignment to the six Fe sites have been determined to be the following sequence: 378(j₂), 346(k₂), 334(j₁), 325(k₁), 322(c), 306(e) kOe. The substitution of Co for Fe decreases the hyperfine fields at all Fe sites. The intensity variations of the subspectra with Co content show that Co atoms have a strong preference to occupy the k₂ site, but have a rather less tendency to enter the j₂ site, which is preferred by Fe atoms.     

Spin-wave resonance in three-layer NiFe/DyxCo1−x /NiFe films as a method for detecting structural inhomogeneities in amorphous DyxCo1−x Layers

The standing spin-wave spectrum was studied by spin-wave resonance in three-layer Ni₈₀Fe₂₀/Dy_xCo_1?x /Ni₈₀Fe₂₀ films with an amorphous interlayer of DyCo alloy in the region of compensation compositions. It is shown that the spin-wave resonance (SWR) spectrum in the geometry k‖M is observed only for a planar system with a DyCo layer of precompensation composition. In the k⊥M geometry, the SWR spectrum was observed for the DyCo systems with both pre-and postcompensation compositions. The exchange stiffness was analyzed as a function of the DyCo layer thickness to formulate a model of microheterophase structure for amorphous DyCo alloys in the compensation region, where the magnetic microstructure accounts for the dynamic and static magnetic characteristics of these materials.     

Scattering of acoustic phonons by rare earth substitutional atoms in yttrium aluminum garnets

The diffusive maxima of phonon signals, and in particular their arrival timest _m are examined for a number of solid solutions of rare earth atoms in yttrium aluminum garnets. The phonon pulses are generated by metallic films of the characteristic lengthl _h heated by current pulses to the temperatureT _h slightly higher than the ambient temperatureT. The injected phonons travel in wafers of the thicknessL _z. They are scattered by substitutional atoms of rare earth occupying the yttrium dodecahedral sites, rare earth and yttrium atoms occupying the aluminum octahedral sites and by another lattice imperfections generated in the process of sample growing. The qualitative analysis based on our exact formula for the diffusion coefficientD allows us to extract the contribution of rare earth atoms substituting the Y atoms toD. Considering the dependence oft _m/L _z ² on the temperature and the ratiol _h/L_z we conclude thatD～T _h ^?4 and that the energy of phonons forming the diffusive maxima ranges from 3.2k _BT_H to 4.2k _BT_H, which is in reasonable agreement with the existing estimates.     

Electronic spectroscopy of N- and C-substituted chlorocarbazoles in homogeneous media and in solid matrix

Electronic spectra (absorption, fluorescence and phosphorescence emission spectra) of chlorocarbazoles 1a-e, 2a-b, 3a, 4a-b, 5a, 6a, 7a, 8a-c, 9a and 9b in acetonitrile and in solid matrix have been recorded at 298 and 77 K. The dynamic properties of the lowest excited singlet and triplet states in term of fluorescence and phosphorescence lifetime, τ_f and τ_p, fluorescence and phosphorescence quantum yield, φ_f and φ_p have been measured in the same experimental conditions and from these data the radiative and the radiationless rate constants (k_f⁰, k_isc, k_f⁰(77), k_isc(77), k_p⁰ and k_nr⁰) and the intersystem crossing quantum yield, φ_isc, were derived.The intramolecular heavy atom effect (HAE) on the spectroscopic data and photophysical rate constant was analyzed and the incorporation of chlorine atoms to the carbazole moiety proved their ability to quench the fluorescence emission by spin-orbital coupling.The values of the HOMO and LUMO energy, the oscillator strength (f) and the λ_max(abs) associated to the electronic transitions, the heat of formation of the chlorocarbazoles and the corresponding radical cation (ΔH_f and ΔH_f(RC)) and the adiabatic ionization potential (I_a) were also calculated by using the semiempirical PM3 method after HF/3-21G geometrical optimization, and were compared with the spectroscopic and photophysical data as well as with the one electron oxidation potential data (E_p/2).     

Magnetization of optically polarized gas atoms by an optical pulse train

The properties of the density matrix and the multipole moments arising in oriented and aligned atoms with zero nuclear spin through the interaction with strong resonant ultrashort pulses with wave vector k ₀ and circular or linear polarization have been found. Calculations have been made for the time-dependent light-induced magnetization μ(t′) of a gas of pre-oriented and prealigned atoms following the passage of a weak resonant elliptically polarized pulse with frequency ω and wave vector k collinear with k ₀. It is shown that for oriented atoms, μ(t′) is an even function of the detuning from resonance, ω-ω _ba, and can be split into two terms whose directions are a consequence of symmetry and are determined by the vectors k ₀ and k as well as by the direction of rotation of the electric fields corresponding to the pulses. For aligned atoms the vector μ(t′) is collinear with k, and the first term is an even function of ω-ω _ba. However, the second term is an odd function of ω-ω _ba and reverses direction when the sign of ω-ω _ba changes, as well as when the orientation of the axes of the polarization ellipse is changed. It is shown that if a series of weak linearly polarized pulses pass through the gas, the light-induced magnetization of the oriented and aligned gas atoms can be decomposed into three factors: the first determines the direction and is a consequence of the symmetry; the second (with the dimensions of magnetic moment) depends on the characteristics of the resonant transitions; and the third is a universal function of t′ and ω-ω _ba that does not depend on the underlying characteristics of the resonant transition. These vector factors and the universal functions are in principle different for oriented and aligned atoms. Zh. éksp. Teor. Fiz. 111, 63–92 (January 1997)