Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV -Ar collisions

Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of “optimized parameters” of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for to 4.02 eV for Ar¹⁰⁺. These values are compared with the results reported by earlier workers and are shown to follow a q²-behaviour up to a charge state q =8+ of the recoil ions. Received: 5 February 1998 / Revised: 8 June 1998 / Accepted: 11 June 1998     

Metastable states of dust plasma

The free energy of three-component dust plasma has been calculated analytically based on the spherical model of an elementary electroneutral volume. It has been shown that metastable states of dust particles, ions, and simultaneously all plasma particles can exist for finite interparticle distances. These states can be attained due to spatial correlation of electrons, while some states can be attained due to the correlation of ions. A large charge of dust particles, high electron temperature, and a small fraction of the charge of the electrons compared to the total absolute charge of the plasma particles are important conditions for the existence of metastable states. A possible connection between the existence of metastable states of particles in the plasma and their agglomeration has been analyzed.     

Charge density at the nucleus and radial behavior of ground state for lithium-like ions with Z = 21 to 30

By using the full-core plus correlation (FCPC) type wave functions, the accurate charge densities ρ(0) at the nucleus and the radial expectation values of the ground states for the lithium-like systems with Z = 21 to 30 are obtained. The determinantal conditions and the electron-nucleus cusp condition are used to calculate the inequalities of the upper and the lower bounds to ρ(0) with two or more expectation values. These inequalities, derived by Angulo and Dehesa [Phys. Rev. A 44 1516 (1991)], are verified to be also valid for these ions with higher nuclear charge. The present results show that the wave functions used in this paper are satisfactory in the whole configuration space for these ions with higher nuclear charge.     

Isotope shifts and hyperfine structure in the transitions of gadolinium

High-resolution resonance ionization mass spectrometry has been used to measure isotope shifts and hyperfine structure in all (J = 2-6) and the transitions of gadolinium (Gd I). Gadolinium atoms in an atomic beam were excited with a tunable single-frequency laser in the wavelength range of 422-429 nm. Resonant excitation was followed by photoionization with the 363.8 nm line of an argon ion laser and resulting ions were mass separated and detected with a quadrupole mass spectrometer. Isotope shifts for all stable gadolinium isotopes in these transitions have been measured for the first time. Additionally, the hyperfine structure constants of the upper states have been derived for the isotopes ^{155, 157} Gd and are compared with previous work. Using prior experimental values for the mean nuclear charge radii, derived from the combination of muonic atoms and electron scattering data, field shift and specific mass shift coefficients for the investigated transitions have been determined and nuclear charge parameters for the minor isotopes ^{152, 154} Gd have been calculated. Received 18 November 1999     

Intensity and detuning dependence of fine structure changing collisions in a 85 Rb magneto-optical trap

In an experimental study, the multi-ionisation of metallic clusters (Na_n) has been analysed in collisions with light ions in low charge states (H⁺, He⁺, He²⁺, O³⁺) at collision velocities below 1 a.u. Cluster ions are produced in charge states up to 5+. The average charge of the nano-particles is found to increase linearly with the variation of projectile velocity and the square of the effective projectile charge, well in agreement with the electronic stopping power of the bulk material. A fraction of 50% to 30% of the total projectile energy loss (decreasing with velocity) is transferred into vibrational modes in good agreement with recent theoretical predictions. Received 8 November 2000 and Received in final form 26 January 2001     

Effect of the initial charge and charge-state fluctuations on the range parameters of high-energy ions

A model used in calculating the depth distribution of implanted atoms, and the energy released into the electron and nuclear subsystems of the solid is studied. It takes into account the initial charge and the fluctuations of charge states of high-energy ions with energies E⩽1 MeV amu⁻¹. The results of calculations are obtained on the basis of solutions of transport equations. Satisfactory agreement between theoretical predictions and experimental results is observed for a broad class of ion-target systems. Zh. éksp. Teor. Fiz. 113, 489–498 (February 1998)     

Electronic and spectral properties of ametal-organic super container molecule by single point DFT

ABSTRACT

Metal-organic super container (MOSC) molecules are ideal candidates for photocatalysis due to their construction with transition metal centres and tuneable cavity sizes that could house catalytic sites. The basic electronic structure for a model of extremely large size (more than 2000 ions) is explored by single point calculation using unrestricted density functional theory, and Perdue–Burke–Ernzerhof functional in Vienna ab initio simulation package software. The information obtained through these calculations (such as density of states, absorbance spectra, and charge density) will allow for analysis of a MOSC's catalytic ability. Electronic characteristics of the nanostructures (MOSCs and their building blocks) in the ground and photoexcited electronic configurations are examined. We explore if the presence of transition metal ions with open shells in such close proximity to one another may result in high spin configurations and show any arrangement into ferromagnetic ordering. Spin-unrestricted computation was applied to evaluate how optical properties could be affected by d–d transitions. A scan of a spin-polarisation parameter allows one to resolve spin configuration and obtain a connection between theory and experiment. Analysis of Kohn–Sham orbitals of interest provides insight into charge transfer mechanisms, which were found to contribute to multiple low-energy charge transfer states to the electronic structure.     

A simple post-accelerator foil stripper assembly for atomic collision experiments

A multiple foil holder for use in ultra high vacuum (UHV) environment as a post accelerator ion stripper has been designed and fabricated. It is used to produce beams of an ion in different charge states at a given energy from a 14 MV pelletron accelerator. These ions are required in several types of atomic collision experiments. The assembly is tested with³²S ions at various energies.     

Energy loss of light ions with allowance for the presence of metastable particles in the ion beam

The change in the average ion charge due to the presence of particles in metastable states in beams of helium-like ions has been studied. The charge distributions and average charges have been calculated for ions with nuclear charges Z = 3?7 and a velocity of 3.65 au in nitrogen. The previously obtained data on the cross sections of loss and capture of electrons by metastable ions and ions in the ground state were used in the calculations. It is shown that the presence of metastable particles in ion beams leads to an increase in the average charge and energy loss for all considered ions.     

Charge states of cobalt ions in nanostructured lithium cobaltite: X-ray absorption and photoelectron spectra

The charge states of ions in nanostructured lithium cobaltite prepared by severe plastic deformation under pressure have been determined using X-ray absorption spectroscopy and photoelectron spectroscopy, as well as calculations of the atomic multiplets with allowance for the charge transfer. It has been found that small deformations (pressures up to 5 GPa and angles of anvil rotation up to 30°) lead to the generation of lithium vacancies in the bulk of the nanostructured material and the formation of the Li₂O phase on the surface. The charge compensation occurs at the expense of holes in oxygen 2p states; the electronic configuration of cobalt ions is 3d ⁶ L, where L is a hole in oxygen 2p states. It has been shown that nanostructured lithium cobaltite belongs to the class of insulators with a negative charge transfer energy. An increase in the degree of deformation of lithium cobaltite (at a pressure up to 8 GPa) leads to the formation of Co²⁺ ions (with the electronic configuration 3d ⁷).     

Transition and rare-earth elements in the SiC and GaN wide-gap semiconductors: Recent EPR studies

EPR studies of transition-element ions in SiC and GaN and of erbium in 6H-SiC are reported. Data are presented on Sc²⁺ ions and scandium acceptors, and chromium and molybdenum ions in various charge states in SiC. A study was made of nickel and manganese in nominally pure GaN grown by the sandwich sublimation method. The first EPR investigation of Er in 6H-SiC is reported. Erbium was identified from the hfs of the EPR spectra. Various possible models of erbium centers in silicon carbides are discussed. Strong room-temperature erbium-ion luminescence was observed. Fiz. Tverd. Tela (St. Petersburg) 41, 865–867 (May 1999)     

Determination of charge states of single swift heavy projectiles by high-energy delta-electrons

The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.     

Field evaporation of impurity ions from a liquid gallium ion source

The charge states of ions emitted from a gallium liquid metal field ion (LMI) source contaminated with tin and copper have been measured. The results for tin show that the proportion of Sn²⁺ to Sn⁺ is much larger than is found for a LMI source of pure tin. A model in which Sn²⁺ is assumed to be produced by post-ionization of Sn⁺ is used to set an upper limit to the electric field at the point of emission. Its value is approximately equal to that predicted by field evaporation theory for a pure gallium source. Consequently the charge states of emitted impurity ions are determined by field strengths imposed by the main component.     

Features of the pre-equilibrium charge states of light ions passing through thin celluloid films

A semi-empirical method for establishing of the average charge of ions passing through thin celluloid films is proposed. Calculations for helium (He) and nitrogen (N) ions with different initial velocities (12?18.7 × 10⁸ cm/s for He and 4?12 × 10⁸ cm/s for N) are presented. The equilibrium thickness of a celluloid target in dependence on the initial charge states of incident ions is evaluated.     

Peculiarities in the cross sections of electron capture by phosphorus ions

The effect of decreasing the cross sections of electron capture by phosphorus (P⁵⁺) ions penetrating through gaseous media has been revealed experimentally. This effect is a violation of the known uniform dependence between the electron-capture cross section and the ion charge. Such an anomaly was not observed in measurements performed with argon ions under the same conditions. A possible reason of decreasing the cross sections of electron capture by P⁵⁺ ions may be autoionization of excited P⁴⁺ ions. The latter are formed during electron capture into excited states by metastable particles of a beam of P⁵⁺ ions.     

Method for calculating the nonequilibrium characteristics of light ions passing through thin organic films

A method is proposed for calculating the charge fractions, mean charges, and dispersion of the charge distribution in ion beams passing through thin organic films under nonequilibrium conditions. Calculations are performed for N ions travelling at different velocities (from 8 × 10⁸ to 12 × 10⁸ cm/s) in celluloid. The energy loss is estimated depending on the initial charge states and velocities of the incident ions.     

Electron multiplicity in slow collisions of Ar ions with C

Electron capture by Ar⁸⁺ in collisions with C₆₀ fullerene has been investigated using coincident measurements of the number n of ejected electrons, the mass and charge of multicharged Cr+ ₆₀ recoil ions and their fragments Ci+ m and the final charge state of outgoing projectiles Ar(8-s)+ (). The number of captured electrons r is the sum of the numbers of stabilized and emitted electrons: r = n + s. The ratio n / s decreases by a factor three with s increasing from 1 to 7 showing that the multiply excited states populated by capture of a large number of electrons are rather stable against auto-ionisation. Each kinetic energy spectrum of Ar⁺ and Ar²⁺ projectiles is composed of two peaks which we attribute to collisions “inside” and “outside” the C₆₀ cage. The measured energy shift of the projectile keV is consistent with the corresponding energy loss keV in a carbon foil with an equivalent thickness. Inside collisions are characterized by a strong dissociation of recoil ions into light monocharged fragments and by a high multiplicity of ejected electrons. Received: 25 March 1998 / Received in final form and Accepted: 9 June 1998     

Possible ground states of rare-earth nickelates (RNiO3, R = La,Nd, Pr): a mean-field study

The ground states of rare-earth nickelates (RNiO₃) are antiferromagnetic insulators except LaNiO₃, which is a strongly correlated metal. Rare-earth nickelates (R ≠ La) undergo a sharp transition from a high-temperature paramagnetic metal to a low-temperature antiferromagnetic insulator at finite temperature T_MI that increases with the increase in atomic number of the rare-earth ions. The magnetic and resistive transitions are coupled for NdNiO₃ and PrNiO₃, but independent for the other members of the series. Whether the antiferromagnetic and insulating ground states of nickelates are due to charge ordering, or orbital ordering, it is a matter of current dispute. The present paper intends to explain the difference in the observed ground states of RNiO₃ compounds, by calculating their band structure and density of states. The experimentally observed ground states of nickelates have been explained on the basis of mean-field calculation and the correlation effect is incorporated in the dynamical mean-field theory thereof.     

Note on electron impact excitation for transition of Be-like isoelectronic sequence

Relativistic distorted-wave method was used to calculate the electron impact excitation collision strengths for transitions 2 s2 ¹ S0-2 s 2 p ³ P1 of Be-like isoelectronic ions. The target states were described, respectively, by 10-level, 46-level and 133-level MCDF configuration-expansion. The relativistic continuum orbitals were calculated in the potential field of frozen target-ion charge distribution with semi-classical exchange potential. The influence of the target states on this collision process along the isoelectronic sequence was investigated in the above three MCDF configuration-expansion modes. It was found that the configurations in the n =3 and the n =4 complexes have great influence on both the high and the low Z ions but the influence is relatively small for intermediate Z ions. The latter phenomenon was attributed to competition between opposing correlation and relativistic effects on the collision strengths. Received: 25 February 1998 / Received in final form: 18 June 1998