Absolute cross-sections and kinetic-energy-release distributions for electron-impact ionization and dissociation of CD<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections have been measured for electron-impact dissociative excitation and ionization of CD₂⁺ leading to formation of CD₂²⁺, CD⁺, C⁺, D₂⁺ and D⁺. The animated crossed-beams method is 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 for CD₂²⁺, CD⁺, C⁺, D₂⁺ and D⁺ respectively. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product, which are of significant interest in fusion plasma edge modelling and diagnostics. Conforming to the scheme recently applied in the CD₄⁺ and in the CD₃⁺ articles, the cross-sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic-energy-release distributions are determined for each ionic fragment at selected electron energies.     

I. Electron-impact ionization and dissociation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact ionization and dissociation of C₂H₂⁺ and C₂D₂⁺ have been measured for electron energies ranging from the corresponding thresholds up to 2.5 keV. The animated crossed beams experiment has been used. Light as well as heavy fragment ions that are produced from the ionization and the dissociation of the target have been detected for the first time. The maximum of the cross-section for single ionization is found to be (5.56 ± 0.03)× 10^-17 cm² around 140 eV. Cross-sections for dissociation of C₂ H₂⁺ (C₂D₂⁺) to ionic products are seen to decrease for two orders of magnitude, from C₂D⁺ (12.6 ± 0.3) × 10^-17 cm² over CH⁺(9.55 ± 0.06) × 10^-17 cm², C⁺ (6.66 ± 0.05) × 10^-17 cm², C₂⁺ (5.36 ± 0.27) × 10^-17 cm², H⁺ (4.73 ± 0.29) × 10^-17 cm² and CH₂⁺ (4.56 ± 0.27) × 10^-18 cm² to H₂⁺ (5.68 ± 0.49) × 10^-19 cm². Absolute cross-sections and threshold energies have been compared with the scarce data available in the literature.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

Absolute cross sections and kinetic energy release distributions for electron-impact ionization and dissociation of CD<Superscript>+</Superscript><Subscript>4</Subscript>

Absolute cross sections for electron-impact dissociative excitation and ionization of CD⁺ ₄ leading to formation of ionic products (CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺, C⁺, D⁺ ₃, D⁺ ₂, and D⁺) have been measured. The animated crossed-beams method is applied in the energy range from the reaction threshold up to 2.5 keV. Around 100 eV, the maximum cross sections are found to be (3.8±0.2) ×10^-19 cm²,  cm², (7.1±0.8) ×10^-17 cm², (9.0±0.8) × 10^-17 cm² and (3.7±0.4) ×10^-17 cm² for the heavy carbonaceous ions CD²⁺ ₄, CD⁺ ₃, CD⁺ ₂, CD⁺ and C⁺ respectively. For the light fragments, D⁺ ₃, D⁺ ₂, and D⁺, the cross sections around the maximum are found to be (5.0±0.6) ×10^-19 cm², (1.7± 0.2) ×10^-17 cm² and (10.6±1.0) ×10^-17 cm², respectively. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. The analysis of ionic product velocity distributions allows determination of the kinetic energy release distributions which are seen to extend from 0 to 9 eV for heavy fragments, and up to 14 eV for light ones. The comparison of present energy thresholds and kinetic energy release with available published data gives information about states contributing to the observed processes. Individual contributions for dissociative excitation and dissociative ionization are determined for each detected product. A complete database including cross sections and energies is compiled for use in fusion application.     

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).     

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 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.     

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.     

Investigating the Double Beta Decay of <Superscript>58</Superscript>Ni

Double beta decay (β + EC, EC/EC) of ⁵⁸Ni is investigated at France’s Modane Underground Laboratory (4800 m water equivalent) using the OBELIX ultralow-background HPGe detector with a sensitive volume of 600 cm³ and a natural nickel sample of ~68% 58Ni with a mass of ~21.7 kg. After preliminary analysis of the experimental data accumulated over ~144 days, new experimental limits are obtained for the 2νβ⁺EC decay of ⁵⁸Ni to the 0⁺ ground state and the 2 ₁ ⁺ , 811 keV excited state of ⁵⁸Fe, and for the 2νEC/EC decay of ⁵⁸Ni to the 2 ₁ ⁺ , 811 keV and 2 ₂ ⁺ , 1675 keV excited states of ⁵⁸Fe. The limits are T_1/2(β⁺EC,0→0⁺) > 1.7 × 10²² yr, T_1/2(β⁺EC,0→2 ₁ ⁺ ) > 2.3 × 10²² yr, T_1/2(EC/EC,0→2 ₁ ⁺ ) > 3.3 × 10²² yr, and T_1/2(EC/EC,0→2 ₂ ⁺ ) > 3.4 × 10²² yr. Experimental limit T_1/2(0νEC/EC–res, 1918 keV > 4.1 × 10²² yr is obtained for resonant neutrinoless radiative EC/EC decay with an energy of 1918.3 keV. All limits are at 90% CL.     

Electron-impact ionization and dissociation of C<Subscript>2</Subscript>D<Superscript>+</Superscript>

Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C₂D⁺)^+) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C₂D²⁺, C²⁺, C₂⁺_2^+ , CD⁺, C⁺ and D⁺. The maximum of the cross section for single ionization is found to be (2.01 ± 0.02) × 10^-17 cm², at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C⁺, over C₂⁺_2^+ and CD⁺ down to that of D⁺. The maxima of the cross sections are obtained to be (14.5 ± 0.5) × 10^-17 cm² for C₂⁺_2^+, (12.1 ± 0.1) × 10^-17 cm² for CD⁺, (27.7 ± 0.2) × 10^-17 cm² for C⁺ and (11.1 ± 0.8) × 10^-17 cm² for D⁺. The smallest cross section is measured to be (1.50 ± 0.04) × 10^-18 cm² for the production of the doubly charged ion C²⁺. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest fragment C₂⁺_2^+, up to 11.0 eV for CD⁺, 14.2 eV for C⁺ and 11.2 eV for D⁺ products.     

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.     

Specific features of steady-state implantation of crystalline silicon with a molecular oxygen-nitrogen beam: Si <Emphasis Type="Italic">L</Emphasis><Subscript>2, 3</Subscript> x-ray emission spectra

The local electronic structure of 〈111〉 n-silicon single-crystal samples is studied using Si L _{2, 3} x-ray emission spectroscopy. The Si _x O _y N _z system is formed by implanting the samples with an ¹⁶O ₂ ⁺ and ¹⁴N ₂ ⁺ ion molecular beam (the oxygen/nitrogen ratio in the molecular beam is 1:1, the implantation energy is 30 keV, the irradiation fluences vary from 2.0 × 10¹⁷ to 1.5 × 10¹⁸ cm^?2, the samples after the implantation are subjected to rapid thermal annealing in nitrogen at 800°C for 5 min). A comparison of the recorded Si L spectra with the spectra of the reference samples reveals clear correlations between the specific features of the electronic structure of the silicon oxynitride formed upon implantation and the ion fluence. It is shown that the implantation at fluences of 2 × 10¹⁷ and 1 × 10¹⁸ cm^?2 results in the predominant formation of Si₃N₄, whereas the implantation at a fluence of 1.5 × 10¹⁸ cm^?2 leads primarily to the formation of SiO₂ layers in single-crystal silicon. The most probable factors and mechanisms accounting for such implantation of ¹⁶O ₂ ⁺ and ¹⁴N ₂ ⁺ into the samples under study are discussed. The experimental data obtained are compared with ab initio full-potential linearized augmented plane wave calculations of the band structure.     

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%.     

H<Subscript>3</Subscript>O<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack> ions with a strong quasi-symmetrical H-bond and their hydration in aqueous solutions of NaOH and KOH

Ion-molecular interactions in aqueous solutions of NaOH (0–47.8%) and KOH (0–51.95%) are studied by multiple frustrated total internal reflection IR spectroscopy. Interpretation of the spectra and analysis of the spectral data are performed based on the results of DFT calculations (B3LYP/6-31++G(d, p)) of the characteristics of the free and double hydrated H₃O ₂ ^- ion. It is established that the changes in the IR spectra of NaOH and KOH aqueous solutions caused by increasing alkali concentration are due to the formation of H₃O ₂ ^- ions with a strong quasi-symmetrical hydrogen bond and their subsequent hydration by one or two water molecules. The influence of the cation nature on the degree of hydration of H₃O ₂ ^- ions is demonstrated. The equilibrium concentrations of monohydrate (H₃O ₂ ^- ? H₂O) and dihydrate (H₃O ₂ ^- ? 2H₂O) are calculated and their IR continuous absorption spectra are isolated.     

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.     

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.     

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.     

Double beta decay of <Superscript>150</Superscript>Nd to the First 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two neutrino double beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with the 400 cm³ low-background HPGe detector. Data analysis for 11320.5 h shows the excess of events at 333.9 and 406.5 keV. This makes it possible to estimate the half-life of the investigated process as [1.4 _?0.2 ^+.04 (stat)±0.3(syst)]×10²⁰yr.     

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.     

Double-beta decay of <Superscript>150</Superscript>Nd to the first 0<Superscript>+</Superscript> excited state of <Superscript>150</Superscript>Sm

Two-neutrino-double-beta decay of ¹⁵⁰Nd to the first 0⁺ excited state in ¹⁵⁰Sm is investigated with a 400-cm³ low-background HPGe detector. Data analysis for 11320.5 h shows an excess of events at 333.9 and 406.5 keV. This allows us to estimate the half-life of the investigated process as [1.4 _?0.2 ^+0.4 ±0.3(syst.)]×10²⁰ yr.