Manifestation of nonuniformity in the electron charge distribution in H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> molecular ions colliding with each other

The anomalous character of threshold properties in the ion-molecule reactions H ₂ ⁺ + H ₂ ⁺ → H ₃ ⁺ + p and H ₂ ⁺ + H ₂ ⁺ → H + p + H + p has been theoretically analyzed. It has been shown that these reactions proceed through the formation of the intermediate H ₄ ⁺⁺ complex. Molecules H ₂ ⁺ in the collision process are described by a chemical model, where the positive charge is concentrated in one of the nuclei. The calculations of the reaction cross sections are in good agreement with the experimental data. It has been shown that the chemical model of the H ₂ ⁺ molecule can be consistently explained only in terms of dynamic interactions, i.e., polarization forces and van der Waals forces.     

Metastable helium cluster He<Stack><Subscript>4</Subscript><Superscript>*</Superscript></Stack>

The existence of a metastable cluster He ₄ ^* with total spin S = 2 is predicted. The cluster consists of two covalently bound excited spin-polarized triplet He ₂ ^* molecules and is rectangular in shape. The electron wavefunctions, the dependence of the energy He ₄ ^* system on the distance between the He ₂ ^* triplet molecules, the atomic spacing, the frequency spectrum of natural oscillations of the cluster, and other characteristics are calculated from first principles. It is shown that the metastable state is formed if one of the excited He ₂ ^* molecules is in the ³Σ _u ⁺ state, while the other is in the ³Π_g state. The radiation lifetime τ of the metastable cluster He ₄ ^* is calculated; it is found to range from 100 to 200 s, which is much longer than the lifetime τ ≈ 20 s of the triplet molecule He ₂ ^* (³Σ _u ⁺ ). The height U ≈ 0.5 eV of the potential barrier preventing the departure from the local energy minimum is determined. The energy E_acc ≈ 9 eV/atom accumulated in the He ₄ ^* cluster is calculated; this energy considerably exceeds the energy of known chemical energy carriers. It is shown that the accumulated energy is released virtually completely during decomposition of the He ₄ ^* cluster into individual helium atoms. This means that helium clusters are a promising material with a high accumulated energy density (HEDM).     

High-frequency EPR of Cr<Superscript>2+</Superscript> ions in CdGa<Subscript>2</Subscript>S<Subscript>4</Subscript>

High-frequency broad-band (65–240 GHz) EPR is used to study impurity centers of bivalent chromium in a CdGa₂S₄ crystal. It is found that the EPR spectra correspond to tetragonal symmetry. The spin Hamiltonian H = βB · g · S + B ₂ ⁰ O ₂ ⁰ + B ₄ ⁰ O ₄ ⁰ + B ₄ ⁴ O ₄ ⁴ with the parameters B ₂ ⁰ =23659±2 MHz, B ₄ ⁰ =1.9±1 MHz, |B ₄ ⁴ |=54.2±2 MHz, g_‖=1.93±0.02, and g_⊥=1.99±0.02 is used to describe the observed spectra. It is concluded that chromium ions occupy one of the tetrahedrally coordinated cation positions.     

Exotic molecular states in a strong magnetic field: H<Stack><Subscript>3</Subscript><Superscript>(2+)</Superscript></Stack> ion

The existence of the molecular ion H ₃ ⁽²⁺⁾ in a magnetic field in a triangular and a linear configuration is discussed. A variational method (with an optimization of the form of the vector potential) is used. It is shown that, in the range of magnetic fields 10⁸<B<10¹¹ G, the system (pppe), with the protons forming an equilateral triangle perpendicular to the magnetic line, has a well-pronounced minimum in the total energy. Also, for B?10¹⁰ G, if the protons are situated along a magnetic line (linear configuration), a well-pronounced minimum in the total energy appears. Both configurations are unstable under the decays H(atom) + p + p and H ₂ ⁽⁺⁾ + p. A possible connection between the H ₃ ⁽²⁺⁾ molecular ion and a recently discovered absorption feature in a neutron-star atmosphere is discussed.     

Optical characteristics of radiation from N<Stack><Subscript>2</Subscript><Superscript>*</Superscript></Stack> dimers in a barrier discharge

The spectral and power characteristics of radiation of the second positive system of nitrogen (C ³Π _u → B ³Π _g ) in Ar-N₂ and Ar-N₂-Cl₂ mixtures excited by barrier discharge have been studied experimentally. Addition of argon to N₂ increased the radiation power by sixfold. In the triple mixture Ar-N₂-Cl₂ = 210/0.5/0.005, minor chlorine additions increased the intensity of the C ³Π _u → _B ³Π _g transition by 26% compared to Ar-N₂ mixtures. Radiation power density of 2.7 mW/cm² has been achieved. In both binary and triple mixtures, the second positive system of nitrogen was the major contributor to radiation, while the contributions of the fourth positive system of N ₂ ^* (D ³Σ _u ⁺ → B ³Π _g ), the Vegard-Kaplan transition of N ₂ ^* (A ³Σ _u ⁺ → X ¹Σ _g ⁺ ), and the D′ → A′ band of Cl ₂ ^* were negligibly small.     

Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections have been measured for electron-impact dissociativeexcitation and ionization of CD ₂ ⁺ leading toformation of CD ₂ ²⁺ , CD⁺, C⁺,D ₂ ⁺ and D⁺. The animated crossed-beams methodis applied in the energy range from the reaction threshold up to 2.5 keV.The maximum total cross-sections are found to be (1.2±0.1)×10^-17 cm², (6.1±0.7)×10^-17 cm², (6.4±0.7)×10^-17 cm², (26.3±3.8)×10^-19 cm² and (14.9±1.4)×10^-17 cm² forCD ₂ ²⁺ , CD⁺, C⁺,D ₂ ⁺ and D⁺ respectively. Individualcontributions for dissociative excitation and dissociative ionization aredetermined for each singly-charged product, which are of significantinterest in fusion plasma edge modelling and diagnostics. Conforming to thescheme recently applied in the CD ₄ ⁺ and in theCD ₃ ⁺ articles, the cross-sections are presented inclosed analytic forms convenient for implementation in plasma simulationcodes. Kinetic-energy-release distributions are determined for each ionicfragment at selected electron energies.     

Secondary ion emission from a GaAs single crystal upon bombardment with Bi<Stack> <Subscript> <Emphasis Type="Italic">m</Emphasis> </Subscript> <Superscript>+</Superscript> </Stack> cluster ions

Secondary-ion mass spectra and energy distributions upon bombarding a gallium arsenide single crystal using Bi_m⁺(m = 1–5) cluster ions with energies of 2–12 keV are investigated. The gallium cluster ion yield grew nonadditively with the number of atoms in the cluster projectiles. A quasi-thermal component found in the energy spectra of secondary Ga⁺ and Ga₂⁺ ions is indicative of the occurrence of the thermal spike mode upon cluster ion bombardment. The quasi-thermal component in the yield of atomic Ga⁺ ions upon bombardment with Bi₂⁺–Bi₅⁺–ions is 35–75%.     

Specific features of the three-electron <Emphasis Type="Italic">KL</Emphasis><Stack><Subscript>2, 3</Subscript><Superscript>2</Superscript></Stack> ionization of silicon atoms upon near-threshold photoabsorption

The shape and relative intensity of the group of the Kα_5–8 satellites (radiative transitions KL _{2, 3} ² )-L _{2, 3} ³ of Si atoms are experimentally studied upon photoabsorption near and far from the KL _{2, 3} ² ionization threshold. The satellites were excited near the ionization threshold by lines of the characteristic L spectrum and bremsstrahlung radiation from Nb and Mo anodes and far from the threshold by the L spectrum and bremsstrahlung radiation from an Ag anode and by monochromatized Kα_{1, 2} radiation from a Ti anode. It is established that the probability P(L _{2, 3} ² ) of formation of two additional 2p vacancies during KL _{2, 3} ² photoabsorption of Si atoms near the energy threshold is by a factor of 1.5 lower than that during photoionization in a more distant energy region beyond the threshold. At the same time, the P(L _{2, 3} ² )/P(L _{2, 3}) ratio remains invariable for the absorbed photons throughout the energy range studied. It is demonstrated that, as the KL _{2, 3} ² ionization threshold is approached, an intensity redistribution occurs among the components of the group of the Kα_5–8 lines, which reflects a decrease in the excitation cross section ratio σ(⁴ P)/σ(² P) of the ⁴ P and ² P terms of the KL _{2, 3} ² configuration. A conclusion is drawn that the effects of suppression of the generation of P terms of higher multiplicity during the KL _{2, 3} and KL _{2, 3} ² near-threshold photoionizations are of a common nature.     

Nonradiative relaxation of photoexcited O<Stack><Subscript>1</Subscript><Superscript>0</Superscript></Stack> centers in glassy SiO<Subscript>2</Subscript>

The processes involved in the excited-state relaxation of hole O ₁ ⁰ centers at nonbridging oxygen atoms in glassy SiO₂ were studied using luminescence, optical absorption, and photoelectron emission spectroscopy. An additional nonradiative relaxation channel, in addition to the intracenter quenching of the 1.9-eV luminescence band, was established to become operative at temperatures above 370 K. This effect manifests itself in experiments as a negative deviation of the temperature-dependent luminescence intensity from the well-known Mott law and is identified as thermally activated external quenching with an energy barrier of 0.46 eV. Nonradiative transitions initiate, within the external quenching temperature interval, the migration of excitation energy, followed by the creation of free electrons. In the final stages, this relaxation process becomes manifest in the form of spectral sensitization of electron photoemission, which is excited in the hole O ₁ ⁰ -center absorption band.     

Study of the formation and unimolecular fragmentation of Si<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>O<Stack><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript><Superscript>+</Superscript></Stack> clusters under ion bombardment

The dependences of the emission and fragmentation of clusters sputtered by Xe⁺ ions from the surface of Si _n O _m ⁺ on the oxygen pressure near the bombarded surface are studied using secondary ion mass spectrometry. It is shown that the process of Si _n O _m ⁺ cluster formation under ion bombardment can be described within the framework of the mechanism of combinatorial synthesis by taking into account the mutual reversibility of the reactions of formation and unimolecular decay.     

Synthesis and electrical properties of new perovskite-like <Emphasis Type="Italic">A</Emphasis>Mn<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript> (A = Ca,Ce, and Sm) compounds

AMn₃V₄O₁₂ (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group \(Im\bar 3\)Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca²⁺–Sm³⁺–Ce³⁺, the valence is redistributed from Ca²⁺Mn₃²⁺V₄⁴⁺O₁₂ to Sm³⁺Mn₃²⁺V₄^3.75+O₁₂, and to Ce³⁺Mn₃²⁺V₄^3.75+O₁₂. The temperature dependences of the electrical resistivity are studied.     

Geometry of the internal dynamics of C<Subscript>2</Subscript>H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> carbocation

Using the symmetry group chain methods, the internal dynamics of the simplest carbocation, C₂H ₃ ⁺ , is analyzed under the traditional assumptions that the equilibrium structures of the carbocation are planar and that the nonrigid motion between them is in-plane. This geometry of the internal dynamics is shown to agree with the data of the microwave spectroscopy on the splittings of rotational energy levels caused by the nonrigid motion. Previously, this statement was based on the model that violated the requirement of self-adjointness of operators of physical quantities.     

On double magicity of the <Stack><Subscript>28</Subscript><Superscript>68</Superscript></Stack>Ni<Subscript>40</Subscript> nucleus

Single-particle energies E _nlj of neutron states in the ₂₈ ⁶⁸ Ni₄₀ nucleus are estimated on the basis of extrapolation of the experimental values of E _nlj in the ^58,60,62,64Ni isotopes. The data obtained are compared with the results of calculation within the dispersion optical model.     

Critical behavior of La<Subscript>0.825</Subscript>Sr<Subscript>0.175</Subscript>MnO<Subscript>2.912</Subscript> anion-deficient manganite in the magnetic phase transition region

For La _0.825 ³⁺ Sr _0.175 ² +Mn³⁺O _2.912 ^2? anion-deficient manganite, the specific magnetization, the dynamic magnetic susceptibility, and the heat capacity are investigated. This material is found to be an inhomogeneous ferromagnet below the Curie point T _C ≈ 122 K, which is much lower than the Curie point determined for the stoichiometric composition (T _C ≈ 268 K). An increase in magnetic field by two orders of magnitude leads to an increase in the Curie temperature by ΔT ≈ 12 K. The presence of oxygen vacancies leads to the frustration of a part, namely, V _fr ≈ 22%, of the indirect Mn³⁺-O-Mn³⁺ exchange interactions, but the spin glass state is not realized. The ferromagnetic matrix of the material under study is characterized by a scatter in the exchange interaction intensities. The heat capacity is found to exhibit an anomalous behavior. Based on the Banerjee magnetic criterion, it is established that the ferromagnet-paramagnet transition observed for La _0.825 ³⁺ Sr _0.175 ²⁺ Mn³⁺O _2.912 ^2? anion-deficient manganite is a second-order thermodynamic phase transition. The mechanism and origin of the critical behavior of the system under investigation are discussed.     

Investigation of low-lying levels of the <Stack><Subscript>4</Subscript><Superscript>8</Superscript></Stack>Be nucleus in the multiquantum approximation of the orthogonal scheme

In the multiquantum approximation of the orthogonal scheme, specific calculations for the energies and radii of the ₄ ⁸ Be nucleus are performed with allowance for all states characterized by the λ=[44] Young diagram, the quantum numbers K_min and K_min+2 of the O(3(A?1)) group, and the quantum numbers E=K+2N (N≤9) of the U(3(A?1)) group. The convergence of the results with respect to the extension of the basis is studied, and the structure of relevant wave functions is revealed. The results of these calculations are compared with the results obtained in the analogous approximation of the unitary scheme.     

Band interaction in <Superscript>162</Superscript>Dy, <Superscript>168</Superscript>Er,and <Superscript>172</Superscript>Yb

Coriolis interaction between levels of two rotational bands in ¹⁷²Yb with K ^π = 2⁺ and 3⁺ and in ¹⁶⁸Er between levels with K ^π = 0^?, 1^?, and 2^? is studied. The values of the interaction parameters are obtained. The mutual influence of two bands in ¹⁶²Dy with ΔK = 2, K _i ^π = 0 ₂ ⁺ and 2 ₁ ⁺ due to Coriolis interaction is demonstrated.     

Mass splitting of neutral <Emphasis Type="Italic">B</Emphasis><Stack><Subscript><Emphasis Type="Italic">d,s</Emphasis></Subscript><Superscript>0</Superscript></Stack> mesons in the framework of the minimal supersymmetric model

The effects of a minimal supersymmetric model with the Yukawa sector of the second type and explicit violation of CP invariance in the Higgs potential occurring during the mixing of physical states in systems of neutral B _d,s ⁰ mesons are considered. The mixing parameter Δm _LS is calculated in the limit of four-fermion approximation with the exchange of charged Higgs bosons (H ^±). This study specifies data presented in [1] and establishes new constraints on \(m_{H^ \pm } \) in this model.     

Search for the double-beta decay of <Superscript>130</Superscript>Te to excited states in <Superscript>130</Superscript>Xe

Experimental limits on the half-lives with respect to the (0ν+2ν) double-beta decay of ¹³⁰Te to excited states in ¹³⁰Xe are obtained by using low-background HPGe detectors. At a 90% C.L., they are 1.6×10²¹, 2.7×10²¹, and 2.3×10²¹ yr for transitions to the 2 ₁ ⁺ , 2 ₂ ⁺ , and 0 ₁ ⁺ levels, respectively.     

Optical and x-ray diffraction studies of the symmetry of distorted phases of the (NH<Subscript>4</Subscript>)<Subscript>3</Subscript>ZrF<Subscript>7</Subscript> crystal

(NH₄)₃ZrF₇ single crystals were grown, and polarization-optical and x-ray diffraction studies were performed on powders and crystalline plates of various cuts over a wide temperature range. Phase transitions are revealed at temperatures T _1↑ = 280 K, T _2↑ = 279.6 K, T _3↑ = 260–265 K, and T _4↑ = 238 K on heating and at T _1↓ = 280 K, T _2↓ = 269–270 K, T _3↓ = 246 K, and T _4↓ = 235 K on cooling. The sequence of changes in symmetry is established to be as follows: O _h ⁵ (Z = 4) ? D _2h ²⁵ (Z = 2) ? C _2h ³ (Z = 2) ? C _i ¹ (Z = 108) ? monoclinic²(Z = 216).     

Dynamics of the magnetic flux component normal to the layers of Bi<Subscript>2</Subscript>Sr<Subscript>2</Subscript>CaCu<Subscript>2</Subscript>O<Subscript>8</Subscript> in a tilted field

High-frequency losses in the strongly anisotropic layered superconductor Bi₂Sr₂CaCu₂O₈ are measured at 600 MHz under a magnetic field rocking about the ab plane. Anomalies in losses and hysteretic phenomena are found while performing periodic rocking, i.e., cycling the magnetic field component normal to the sample surface. Based on these observations, conclusions are drawn about the nature of magnetic-flux penetration into the superconductor. It is found that, in the range between 60 K and T _c , the dynamics of magnetic-flux vortex lines normal to the ab plane in the presence of a constant magnetic field applied parallel to this plane is governed by the critical penetration field H _c ^⊥* and the surface barrier in the presence of thermally activated vortex motion (giant flux creep). The dependences of H _c1 ^⊥* and the characteristic field of the surface barrier on the magnitude of the parallel magnetic field are measured.