Average Energy Loss Measured in Single and Double Electron Capture Collisions of He^2＋ on Ar at Low Velocities ＊

Employing the recoil ion momentum spectroscopy we investigate the collision between He^2＋ and argon atoms. By measuring the recoil longitudinal momentum the energy losses of projectile are deduced for capture reaction channels. It is found that in most cases for single- and double-electron capture, the inner electron in the target atom is removed, the recoil ion is in singly or multiply excited states （hollow ion is formed）, which indicates that electron correlation plays an important role in the process. The captured electrons prefer the ground states of the projectile. It is experimentally demonstrated that the average energy losses are directly related to charge transfer and electronic configuration     

Experimental investigation on field evaporation of singly and doubly charged rhodium

Field ion mass spectrometry and field ion appearance spectroscopy are used to analyze field evaporation processes of singly and doubly charged rhodium ions. Field strengths were ranged between 17 and 41 V/nm at tip temperatures between 600 and 100 K. The appearance energies of doubly charged species were found to increase with increasing field strengths from 29.5 ± 0.4 to 32.0 ± 0.2 eV, those of the singly charged species from 11.2 ± 0.1 to 12.4 ± 0.1 eV. Activation energies as determined from measured temperature dependences of the ion counting rates are equal for both kinds of ionic species and decrease from 1.5 to 0.05 eV with increasing field strengths. The observed field dependences cannot be predicted from the image hump model of field evaporation. Evaporation of Rh¹⁺is better understood using the charge exchange model. Generation of Rh²⁺ is described by the postionization of Rh¹⁺ within the frame of a simple potential energy model from which the average interaction energy of rhodium surface atoms with their nearest neighbours may be derived.     

Correlated electron effects in low energy Sr(+) ion scattering

Resonant charge transfer during low energy ion scattering reveals correlated-electron behavior at high temperature. The valence electron of a singly charged alkaline-earth ion is a magnetic impurity that interacts with the continuum of many-body excitations in the metal, leading to Kondo and mixed valence resonances near the Fermi energy. The occupation of these resonances is acutely sensitive to the surface temperature, which results in a marked temperature dependence of the ion neutralization. We report such a dependence for low energy Sr(+) scattered from polycrystalline gold.     

Study of the angular and energy distributions of Na+ and K+ ions which have passed through thin copper films

The angular and energy distributions of alkaline Na⁺ and K⁺ ions which have passed through thin Cu films in different crystal states are studied. The ion energy E₀ is varied from 10 to 40 keV, and the incidence angle. ranges from 0° to 60°. The angular aperture of the detector is ～0.5°, which allows the form of the angular distribution of ions which have passed through the solid thin films as a function of the energy, the angle of primary-ion beam incidence, and the layer thickness to be studied in detail. It is shown that, in the range E₀ = 10.40 keV, the energy loss ΔE of those ions that have passed increases linearly as the energy of incident ions increases. The energy loss increases with increasing ion mass in the case of singly charged ions. The surface amorphization of single- and polycrystalline films leads to an increase (by 150–200 eV) in the energy loss caused by the diffuse propagation of ions and to loss-peak broadening. It is probable that surface amorphization is accompanied by an increase in the number of atoms experiencing multiple collisions with atoms of the film, which leads to an increase in the average energy loss by ions that have passed through films.     

Excitation and deexcitation of the Gd II octet states

Excitation of the octet states of a singly charged gadolinium ion in e-Gd collisions is experimentally studied by measuring 48 excitation cross sections at an electron energy of 30 eV. Four optical excitation functions are obtained within the 0-200-eV electron energy range. The validity of experimental data on the radiative transition probabilities is analyzed in terms of the feasibility of their use for determination of the branching ratios.     

Excitation of even triplet levels of YII in the e-Y collisions

The excitation of high-lying triplet levels of a singly charged yttrium ion by electron-atom collisions is studied experimentally. The parity of the levels studied coincides with the parity of the initial state YI. Forty one excitation cross sections with simultaneous single ionization are measured for an exciting electron energy of 50 eV. The optical excitation functions (OEF) are recorded for the majority of transitions in the electron energy range 0–200 eV. The total cross sections are determined for 20 energy levels. Possible channels of a simultaneous excitation-ionization process are discussed.     

Energies,charges, and sizes of clusters under ion sputtering of a metal

A theory of ion sputtering of a metal in the form of neutral and singly charged clusters with a number of atoms of N ⩾ 5 has been developed. This theory is based on simple physical assumptions and agrees well with experiment. The results are presented in the form of expressions convenient for practical use. The energy spectra of clusters, charge distributions, ionization coefficients, and total yields of neutral and singly charged clusters at different target temperatures are calculated in terms of the proposed theory as an example.     

Formation of excited singly charged barium ions in collisions of slow electrons with barium dibromide molecules

The method of extended crossing beams is used to study inelastic collisions of slow electrons with barium dibromide molecules. The resulting optical emission spectrum contains only the spectral lines of the singly charged barium ion. At an exciting electron energy of 100 eV, the cross sections of dissociative excitation for nine spectral lines of BaII are measured; for all these lines, the optical excitation functions over an electron energy range of 0 to 100 eV are recorded. The possible channels of the dissociative excitation of BaII are discussed.     

Formation of the ion fraction of keV-Energy argon ions upon double scattering by al, Ge, and in targets

The charge fraction of Ar⁺ ions singly or doubly scattered by Al, Ge, and In targets is studied by means of low-energy ion scattering spectroscopy. It is shown that the behavior of the ion fraction is not described by the electron tunneling model in the case of forward scattering by an Al target. The characteristic velocities of ions singly and doubly forward and back scattered by Ge and In targets are found.     

Langmuir Probe in Non‐Maxwellian Plasma: Correlation Between the Electron Energy Distribution Function,the Ion Energy at the Sheath Edge and the Floating Voltage

This work is devoted to the study of the Langmuir probe in non‐Maxwellian plasma, assuming mono‐energetic singly charged ions and a collisionless sheath. Using a general analytical equation for the Electron Energy Distribution Function (EEDF), we study the effect of the EEDF profile on: a) The ion energy at the sheath edge of a negatively biased collector, b) the I‐V probe characteristic and c) the floating voltage (V_p‐Vf). Different methods are used and compared to determine these parameters or characteristics. A correlation is given between the floating voltage, the ion energy at the sheath edge and the EEDF profile. The study is also extended to distribution functions with several components. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Excitation of singlet levels of a singly charged scandium ion in e-Sc collisions

The excitation of singlet levels of the singly charged scandium ion is experimentally studied in collisions of slow electrons with scandium atoms. At the exciting electron energy of 30 eV, 59 excitation cross sections are measured. In the electron energy range of 0–200 eV, seven optical excitation functions are recorded. On the basis of these data the total excitation cross sections are calculated for 11 even and 9 odd levels of Sc II, as well as the contribution of cascade population to 8 even and 7 odd levels.     

Mass-selective trapping of pulsed charged particle beams

The phase-space method is used to evaluate the mass-selective ion confinement properties of the radio-frequency (rf) quadrupole ion trap with phase-synchronized switching-on of the driving rf field for pulsed ion injection from an external source. The results are of interest for on-line investigations of both short-lived isotopes and stable highly charged ions. In particular, singly charged ions with an energy of 10 eV and a mass in the neighborhood of 100 amu, injected along the gap or through an aperture on one of the electrodes, are considered. Mass-selective storage of the injected ions is possible for any trap operation point within the stability region by allowing a field-free drift distance before ion injection. It is shown that after appropriate scaling the results apply to the trapping of any pulsed beam of charged particles.     

Dissociative excitation of the singly charged manganese ion in collisions of electrons with manganese diiodide molecules

The dissociative excitation of the singly charged manganese ion in collisions of electrons with MnI₂ molecules is experimentally studied. At exciting electron energy of 100 eV, 16 dissociative excitation cross sections were measured. The studied transitions occur within the quintet and septet term systems in the absence of intercombination transitions. The measured values of the cross sections are compared to similar values obtained previously in studies of e–MnCl₂ and e–MnBr₂ collisions.     

High-intensity femtosecond laser absorption by rare-gas clusters

The energy absorption efficiency of high-intensity (～10^{16}W/cm^2) femtosecond laser pulses in a dense jet of large rare-gas clusters has been measured. Experimental results show that the energy absorption efficiency is strongly dependent on the cluster size and can be higher than 90%. The measurement of the ion energy indicates that the average ion energies of argon and xenon can be as high as 90 and 100keV, respectively. The dependence of the average energy of the ions on the cluster size is also measured. At comparatively low gas backing pressure, the average ion energies of argon and xenon increase with increasing gas backing pressure. The average ion energy of argon becomes saturated gradually with further increase of the gas backing pressure. For xenon, the average ion energy drops a little after the gas backing pressure exceeds 9 bar (3.2×10^5 atoms/cluster). The result showing the existence of a maximum average ion energy has been interpreted within the framework of the microplasma sphere model.     

Statistical dynamics of direct three-body recombination of heavy ions in the presence of argon and xenon atoms

Recombination of singly charged heavy Cs⁺ and Br^– ions with stabilization with neutral Ar or Xe atoms was studied by the classic trajectory method in the range of ion collision energy and third body energy from 1 to 10 eV. The elementary reaction of recombination was studied on the potential energy surface (PES), which quantitatively reproduces the experimental results of collision-induced dissociation of CsBr molecules (the reverse of recombination). An analysis of the statistically reliable number of trajectories revealed a complex multifactor dynamics of recombination, which involves various mechanisms whose realization depends both on the mass and energy ratio of colliding particles and on the PES structure and spatial configurations of collision determined by impact parameters, orientation angles, etc. The molecules that formed as a result of recombination have nonequilibrium vibrational energy distributions and rotational energy distributions comparable to equilibrium.     

The dissociative excitation of singlet levels of the singly charged lanthanum ion in collisions of electrons with lanthanum bromide molecules

The method of extended crossing beams was used to study inelastic collisions of slow electrons with LaBr₃ molecules. Dissociative excitation caused the appearance of spectral lines of the singly charged lanthanum ion. 38 dissociative excitation cross sections of LaII spectral lines (upper singlet levels) were studied at a 100 eV exciting electron energy. Three optical excitation functions were recorded over the electron energy range 0–100 eV. The cross sections obtained are compared with the data on dissociative excitation cross sections of the LaCl₃ molecule.     

Ionisation and fragmentation of tetraphenyl iron (III) porphyrin chloride induced by slow multiply charged ion impact

Ionisation and ion-induced fragmentation of tetraphenyl iron (III) porphyrin chloride (FeTPPCl) molecules have been studied after slow collisions (v∼ 0.2 a.u.) with multiply charged ions (O³⁺, Ar⁸⁺). Intact molecules and large fragments are observed in charge states up to q=4. For q=1, the intact molecule is the most abundant species, in particular, when projectiles in higher charge states are used. When the internal energy of the singly charged ion is increased by the energy transfer during the collision, the singly charged system de-excites by the emission of a neutral Cl-atom, a free electron or possibly a negative Cl anion. The processes are observed as direct as well as delayed processes on a μs-time scale. For q=2 to 4 the loss of the Cl-atom and some phenyl groups becomes more likely due to the lower stability and the larger energy transfer. The charge state distribution of atomic fragments is found to be very different, in particular, when C^q+ and Cl^q+ ions are compared. In the first case mainly singly charged ions are detected, whereas in the second case ions in charge states up to q=6 are observed with high intensities. These phenomena are discussed in terms of the intramolecular charge mobility.     

EICO measurements of inner-core excited mixed rare-gas clusters

The spectra of deep inner-core excited mixed rare-gas clusters were recorded by using electron ion coincidence (EICO) and multi-hit momentum imaging (MHMI) techniques. The EICO spectra for Ar₉₉Kr₁ clusters reveal that singly charged ions are emitted from the inner-core excited clusters in addition to the multiple charged ions. The dependence of the EICO spectra on photon energy and cluster size suggests that the holes created through vacancy cascade on the krypton atoms are transferred to the surrounding atoms, and that the singly charged ions are the primary product of the krypton photoabsorption. Charge localization is suggested for the inner-core excited mixed rare-gas clusters from the analysis of the EICO peak width. The MHMI measurements give us direct evidence for the strong charge migration from X-ray absorbing atoms to surrounding atoms. The photon energy dependence of the PSD image for fragment ions suggests that the momentum of the fragment ions depends on the number of charges generated by the vacancy cascade.     

The energy spectra of secondary ions emitted during ion bombardment

Secondary ion energy spectra have been measured for singly charged ions emitted from targets irradiated with 43 keV A⁺ ions. Targets studied include the 3d transition metals (Sc, Ti, V, Cr, Fe, Ni) Cu and Zn, Zr, Al and Si and the compounds SiO₂, Al₂O₃, NaCl, KCl. Energy spectra were measured in the energy range 1–600 eV. In several cases a peak in the energy spectrum in the region around 200 eV has been found. This is in addition to the usual low energy peaks in the region of 5–10 eV. In many cases the low energy peak was observed to decay steadily with irradiation time or to increase with oxygen pressure. In the case of the cleanest Zn spectrum, only the high energy peak can be detected. The data are discussed in relation to current models of secondary ion emission. We conclude that, in general, elemental metal targets which are clean are characterised by the high energy peak in the secondary ion energy spectrum. The slower ions emitted have been neutralised by electron exchange processes. The low energy peaks in unclean, partially clean, oxide coated or compound targets (NaCl, KCl) arise because the neutralisation of the slower ions is either not as efficient or is not possible. The secondary ion emission model of Blaise and Slodzian could account for the emission of ions from most targets.