Control of dissipation of energy via reservoirs of coherent states

Dynamic profiles of various chemical reactivity indices like chemical potential, chemical hardness, electrophilicity, susceptibility, etc., within a confined environment during the interaction of atoms with strong oscillating time dependent magnetic fields have been studied. In the present study hydrogen and helium atoms in ground state (n = 1), as well as in excited state (n = 20) are considered. Time-dependent Schrödinger equations are solved for the ground and excited states of hydrogen atom and the Rydberg state of the helium atom while a generalized nonlinear Schrödinger equation is solved for the ground state of the helium atom. Dirichlet type boundary condition has been used to implement confinement to the systems. With an increase in the degree of confinement the system gets harder and hence becomes more stable. Keeping the confinement radius fixed, systems get more stabilized in strong field compared to weak field.     

Ab initio study of formation, migration and binding properties of helium-vacancy clusters in aluminum

Ab initio calculations based on density functional theory have been performed to study the dissolution and migration of helium, and the stability of small helium-vacancy clusters He_nV_m (n, m=0-4) in aluminum. The results indicate that the octahedral configuration is more stable than the tetrahedral. Interstitial helium atoms are predicted to have attractive interactions and jump between two octahedral sites via an intermediate tetrahedral site with low migration energy. The binding energies of an interstitial He atom and an isolated vacancy to a He_nV_m cluster are also obtained from the calculated formation energies of the clusters. We find that the di- and tri-vacancy clusters are not stable, but He atoms can increase the stability of vacancy clusters.     

Doppler-free optogalvanic spectroscopy using an infrared color center laser

We have used a cw color center laser near 2.6 μm to study highly excited states in helium and neon atoms by Doppler- free intermodulated optogalvanic spectroscopy in a hollow cathode discharge tube. For helium n = 4 to 6 transitions, the resolution was limited to about 320 MHz (FWHM) by Holtzmark broadening due to the presence of charged particles in the discharge. Lines as narrow as 60 MHz were observed for neon 3s₅-5p₁₀.     

Mechanochemical penetration of helium atoms into Pd84.5-Si15.5 and Ni78-Si8-B14 eutectic amorphous films extended in liquid 3He and 4He

The penetration of helium atoms into amorphous films extended to fracture in liquid helium has been investigated. It is found that helium atoms penetrate into the eutectic alloy films Pd_84.5-Si_15.5 in ³He (T=0.5 K) and Ni₇₈-Si₈-B₁₄ in ⁴He (T=4.2 K). The spectra of helium liberation from these materials after deformation are obtained upon dynamic (4–5 K/min) annealing at T=293–1323 K. The maximum amount of helium is observed in the regions of local plastic microshears running across the whole width of films and also in the sample regions containing fracture macrocracks and isolated groups of slip bands. The spectra of helium liberation from different regions of destroyed samples show several peaks that correlate with the temperatures of crystallization and melting of the studied films. The data obtained are interpreted within the model of mechanochemical penetration of helium atoms through the dynamically excited dislocation-like defects, which are typical of the amorphous films under consideration.     

On the mechanisms of formation of excited hydrogen atoms in a decaying helium-hydrogen plasma

We spectroscopically studied the population of the excited hydrogen atomic states with the principal quantum numbers n=3 and 4 in a decaying plasma produced by a pulsed discharge in a mixture of helium (p=40.4 Torr) with a small amount of hydrogen ([H₂]≈10¹² cm^?3). Experiments on recording the response of the spectral line intensities to a short-duration electron temperature perturbation revealed the contribution of electron-ion recombination to the population of the H*(n=3) states in the early afterglow. The ions produced by collisions of hydrogen molecules with metastable He(2³ S ₁) atoms, whose density decreases relatively rapidly with time in the decaying plasma, were assumed to be involved in this process. No population of the H*(n=4) atomic levels due to electron-ion recombination was found. Our experimental results are consistent with the conclusions of previous studies that excitation transfer during collisions of metastable helium molecules with hydrogen molecules plays a major role in the population of the excited hydrogen atomic states both with n=3 and with n=4 during most of the afterglow.     

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.     

Velocity dependence of the chemi-ionization of H2O and D2O on impact of 21S and 23S helium atoms

The velocity dependence for the ionization of H₂O and D₂O to form H₂O⁺ and D₂O⁺ in collisions with both 2³S and 2¹S metastable helium atoms has been measured in a crossed molecular beam apparatus using a mechanical velocity-selector on the metastable beam. The cross-sections are found to be proportional to the —n power of the relative collision energy, with n ? 0.4 for both metastable atoms in both gases. The branching ratios H₂O⁺/OH⁺ and D₂O⁺/OD⁺ were both found to be 4.3 for both metastable helium atoms, and to be independent of the relative collision energy.     

The collisional-radiative model and laser-induced excitation transfer in helium plasmas: Role of associative ionization

The effect of associative ionization processes on temporal enhancement and decay of fluorescence from helium levels following laser-induced selective excitation is investigated through a collisional-radiative model. In low-temperature moderate-pressure helium plasmas the associative ionization processes significantly affect the population densities; the effect is more pronounced in n = 3 than in n = 4 levels.     

First-principles study of the crystal structures and electronic properties of LaNi5TxHey tritide

The micro-arrangement of helium atoms and electronic properties of tritides LaNi₅T_xHe_y (x=5, 5.5, 6, 6.5; y=0.5, 1.0) have been systematically investigated by means of the full-potential linearized augmented plane wave (FLAPW) method with the generalized gradient approximation (GGA). Those optimized results indicate that helium atoms prefer to occupy the tetrahedral interstitial sites (6c₁) in LaNi₅ tritides. From the analysis of the electronic structure, a strong and narrow peak appears in the low energy region (about −4.0 eV), which is due to the contribution of the He-s band. With increasing in the helium content, the empty band in the low energy region gradually moves to the right. Compared with H atoms, the interactions between He atom and La, Ni atoms are quite weaker, which can easily cause the pulverization of the host alloy.     

Dynamic diffusion of helium into various types of solids during their deformation and dispersion

Quantitative relations governing the penetration of helium atoms into various types of solids in the course of their plastic deformation in liquid ³He (T = 0.6–1.8 K) and ⁴He (T = 4.2 K) and dispersion in gaseous helium at 300 K were obtained and analyzed. Experiments were carried out on metals with different lattice types, ionic single crystals, amorphous alloys, and barite and titanium dioxide powders dispersed in helium. Curves illustrating helium extraction from deformed specimens under dynamic annealing were obtained. The temperature range of helium extraction was found to correlate with the melting temperature and the initial and deformed structures of a material, which determine the number and character of helium traps present in the material. The dependence of helium penetration intensity on the type of defects forming under plastic deformation for various materials, as well as the formation of chemical bonds of helium atoms to the defected structure of these materials, is discussed.     

Effect of the optical orientation of spin angular momenta of sodium atoms in the 32 S 1/2 state and metastable helium atoms in the 23 S 1 state on the Na-He gas-discharge plasma conduction

The observation of the effect of mutual orientation of spin angular momenta of sodium atoms in the 3² S _1/2 state and helium atoms in the 2³ S ₁ state on the electrical conduction of a Na-He gas-discharge plasma is reported. In the experiments, a simultaneous optical orientation of atoms by the optical emission of sodium and helium lamps was carried out. The influence of the mutual orientation on the conduction was observed as a change in the high-frequency voltage across electrodes of a gas-discharge camera caused by the destruction of orientation of sodium atoms. The effect is explained by the dependence of Penning ionization in the interaction of sodium and helium atoms on the mutual orientation of spin angular momenta of partners.     

Perturbation theory in terms of electron density

When an inhomogeneous electron gas is subjected to a perturbation, its energy and density both change by small amounts. We calculate the changes in the energy explicitly in terms of the density changes within the density-functional theory of many-electron systems. We also derive the equations for the induced densities, and using these show that a density correct up to order n in terms of the perturbation parameter is sufficient to give energy changes up to order (2n + 1). As a corollary, the even-order energy changes E⁽²ⁿ⁾ are variational with respect to the density changes ?⁽ⁿ⁾. The equations for the induced densities also follow from this corollary. The even-order corollary also gives a variational method of calculating the induced densities. The theory is demonstrated by applying it to calculate the polarizability and hyperpolarizability of the hydrogen, helium and neon atoms.     

氦原子1sns组态能量及其相对论修正

利用Mathemtica语言开发了一套计算氦原子1sns组态能量的程序.提出了构造氦原子1sns组态波函数的新方法,利用Rayleigh-Ritz变分法对氦原子1sns(n=2—5)组态的非相对论能量进行了计算,并计算了其相对论修正值(包括质量修正、单体达尔文修正、双体达尔文修正、自旋-自旋接触相互作用修正、轨道-轨道相互作用修正),计算结果与实验值相当接近. 关键词： 氦原子 能量 变分法 Mathemtica程序     

Role of atomic inelastic collisions in a Cs-He steady state discharge

The population of various excited states and the electron temperature in a mixture of cesium vapor and helium have been measured spectroscopically in a stationary electrical discharge where helium atoms remain in their ground state. An equilibrium between the populations of highly excited cesium levels was observed to be characterized by a Boltzmann temperature equal to the gas temperature. It is concluded that the populations of these high levels are more influenced by Cs¹+He inelastic collisions than by Cs¹+e collisions when [He]/[e]?10⁶. The influence of the helium atoms has also been observed on the relation between electron temperature and electron density.     

The Debye-Waller factor in helium scattering by a crystalline surface

On the dense face of a metallic crystal or the (001) face of lithium fluoride, the distance between nearest neighbours is of the same order of magnitude as the helium diameter. The hypothesis of simultaneous interaction between incident helium atoms of thermal kinetic energy and surface atoms belonging to a surface unit cell is therefore introduced. Then the exponent of the Debye-Waller factor contains mean square and mean correlated displacement between atoms of the cell. This gives for the (00) peak an apparent surface Debye temperature Θ_sa higher than the corresponding value usually deduced for instance from LEED measurements. For the (001) face of copper the calculated value is: 323 < Θ_sa < 354 K according to the value ascribed to bulk Debye temperature. On this face, recent experimental results show that helium atoms are coherently scattered in the specular (00) peak. From its intensity analysis is deduced an attractive well depth of 0.009 ± 0.002 eV and Θ_s = 370 ± 10 K, very close to the calculated result. The simultaneous interaction implies that the one phonon exchange can only take place with phonons of long wavelength. This theoretical expectation seems to be in qualitative agreement with experimental data.     

Detection par photoionisation des niveaux de rydberg nF dans le sodium

By three-step optical excitation levels nF, up to n = 32, of sodium atoms of an atomic beam, are populated. The excited atoms are simultaneously photoionized and detected by ion counting. The energies of the observed levels have been roughly measured.     

Infrared optogalvanic spectroscopy in the helium positive column using an F-center laser

Using optogalvanic spectroscopy with a tunable cw F-center laser, we have detected helium transitions from the n=4 to the n=6 states between 2.61 μm and 2.7 μm. The observed sensitivity is in agreement with the predictions of a steady state model of the positive column discharge.     

Electron momentum distribution in multiply-ionized neon atoms

We present momentum-space properties of multiply ionized neon atoms as a function of the degree of ionization of the atom. In particular, we have calculated the Compton profiles of all possible ionized states of neon atoms with electronic configurations 1s^m2sⁿ2p^q, m=1-2, n=0-2, q=0-6. The radial single-electron radial wave functions, obtained from the Hartree-Fock atomic model, were converted into momentum space wave functions by applying appropriate Fourier transformation. The values of the Compton profiles from the present calculation can be used to interpret experimental cross sections of variously ionized neon atoms colliding with other atoms. Compton profiles of neutral neon atoms, available in the literature, are in excellent agreement with the present calculation.