Ensemble Of Ions Research Articles

CLASSICAL DYNAMICS OF THREE IONS WITH COLLINEAR CONFIGURATION IN A PAUL TRAP

We have studied the properties of the classical dynamics of three ions with collinear configuration in a Paul trap.We found that no chaotic motion exists,and the motions of the ions are regular at any given energy E.The trajectories of the ion ensemble in phase space are of the anti-symmetric type and symmetric type periodic(or quasi-periodic) orbits,which are constrained in two KAM tori respectively.The simplest trajectories of the ensemble are periodic orbit A and periodic orbit S.When E tends toward the minimum energy Emin=3.0 of the ensemble,the motions of A orbits and S orbits tend towards the anti-symmetric and symmetric harmonic oscillations,respectively.

Covariance Mapping of Ammonia Clusters: Evidence of the Connectiveness of Clusters with Coulombic Explosion

Direct evidence is reported of the connectiveness of charged clusters with highly charged species (N4+, N3+, and N2+) produced upon the interaction of molecular ammonia clusters with an intense femtosecond laser beam (∼1015 W/cm2 at 120 fs). The value of covariance analysis as a general technique for studying dynamical processes in clusters is demonstrated through elucidating the details of various Coulomb explosion events. Positive covariance determinations identify concerted processes such as the concomitant explosion of protonated cluster ions of unsymmetrical size, while anticovariance mapping is exploited to distinguish competitive reaction channels such as the production of highly charged nitrogen atoms formed at the expense of the protonated members of the cluster ion ensemble. The present study demonstrates the great potential which covariance analysis offers in identifying the precursors and products of dynamical events in clusters and in the present case provides further support to the ignition ...

Collision induced dissociation of doubly charged silver clusters Ag n 2+ , n=21,22,23

Doubly charged silver clusters Agn 2+, n=21, 22, 23, are produced by electron bombardment of an Agn + ensemble stored in a Penning trap. After mass selection the clusters are subjected to collision induced dissociation. The fragmentation channels are determined by time-of-flight mass spectrometry after ejection of the resulting ion ensemble from the trap. Monomer evaporation is the only decay path observed.

Multiparticle Simulation of Ion Injection into the Quadrupole Ion Trap Under the Influence of Helium Buffer Gas Using Short Injection Times and DC Pulse Potentials

The motion of an ensemble of ions during their gated injection into the three-dimensional radio-frequency quadrupole ion trap was simulated considering helium buffer gas collisions, injection at certain RF phase angles and using DC impulsive fields to optimize the trapping efficiency. Simulations using a simple model of ion–neutral collisions show that buffer gas alone, even at 1–10 mTorr pressure, is not able to remove sufficient kinetic energy from the injected ions through ion–neutral collisions to prevent their loss and does not solve the problem of low efficiency of ion retention in the trap, even under qz-optimization. Accumulation of ions over long periods is not very effective, in such cases trapping efficiencies are less than 5%. It is shown that under RF phase angles between 110° and 220° the injected ions can be trapped, although only temporarily, with very high efficiencies. The simulations lead to the conclusion that all of the desired injected ions covering a wide mass/charge range can be trapped for indefinite times when short injection pulses are used together with dipolar DC pulses applied during injection. The additional damping achieved through these dipolar DC impulsive fields and the resulting cooling of the ion cloud is shown to give efficient trapping.

Stochastic simulations of the quantum Zeno effect.

We perform stochastic simulations of the quantum Zeno effect experiment of the type realized with trapped cooled ions. The results are carefully examined for the case where the experiment is performed on a single atomic particle. The results of the simulations for a single ion exhibit the probabilistic behavior that is required to satisfy the collapse of the wave-packet hypothesis. When a large ensemble of ions is described by the simulations, the results are the same as those produced using the density-matrix method. In this way the stochastic simulation methods provide a link between these two approaches, as they are compatible with each in the appropriate regime. The results are also discussed in terms of what may be observed experimentally given the practical limitations of performing experiments with individual ions.

High temperature thermodynamics and oxygen permeability of PrBa 2Cu 3O 6 + x

The pressure-composition isotherms for oxygen in PrBa 2Cu 3O 6 + x were measured by means of coulometric titration in the temperature range 550–825 °C and at oxygen pressures between 10 −3 and 1 atm. The composition dependences of thermodynamic potentials reveal substantially non-ideal behavior of the ensemble of the oxygen ions in the basal plane. The oxygen ion conductivity of the PrBa 2Cu 3O 6 + x compound was measured by a permeation technique in the temperature range 600–850 °C and at oxygen pressures between 0.08 and 1.00 atm. The data were employed for calculation of the oxygen chemical diffusion coefficient. The activation energy of the oxygen conductivity and oxygen diffusivity was found to depend linearly on the oxygen content, U = 2.46 − 1.57 x (eV), in the integral 0.35 < x < 0.60 which was explained by interaction of movable oxygen ions.

Evolution of an ion cloud in a Fourier transform ion cyclotron resonance mass spectrometer during signal detection: its influence on spectral line shape and position

The factors responsible for temporal variation of the detected frequency in an FT ion cyclotron resonance (ICR) spectrometer are analysed. The time-dependent frequency behaviour is believed to be caused by a change in ion cloud configuration, the number of detected ions, and the ion cloud position in the electric field of the ICR cell. The spectral peak shape is calculated for an ensemble of non-interacting ions distributed over amplitudes of axial oscillations. The influence of the Coulomb interaction on the signal and the spectral peak shape is studied by a computer simulation using a highly parallel computer.

Electric double layer at a metal/electrolyte interface: A density functional approach

The structure of electric double layer at a metal/electrolyte interface is studied here using a density functional approach for the metallic electrons as well as the ions of the electrolyte. The metal is represented by a jellium and the electrolyte is modeled as an ensemble of charged hard sphere ions. The minimization of the total energy which includes the interaction of metallic electrons with the electrolyte ions yields the electron and the ion density distribution at the interface. The calculated interfacial capacitance compares quite well with the reported experimental results.

Self-excitation of magnetic islands

A mechanism of island self-excitation is discussed in detail, by studying the dynamical interaction, in a tokamak plasma, of a suitably defined ensemble of ions with the electrostatic field of densely packed island chains, assuming that the ion Larmor radius is larger than the island width. It is shown that the loss of particle kinetic energy, consequent to a transverse adiabatically slow drift produced by the interaction, drives an instability through which this energy is pumped directly into the islands. In this way the islands feed themselves through the ion-chain interaction

Die Kristallstruktur des Lithium-Benzamidinats {Li3[C6H5 - C(NSiMe3)2]3 · NC - C6H5} / The Crystal Structure of the Lithium Phenylamidinate {Li3[C6H5 - C(NSiMe3)2]3 · NC - C6H5}

Abstract Single crystals of the title compound have been prepared by the reaction of benzonitrile with LiN-(SiMe3)2 in hexane and subsequent evaporation of the solvent. Space group P21/n, Z = 4, structure solution with 7945 observed unique reflections. R = 0.052. Lattice dimensions at -70 °C: a = 1485.2(9); b = 2486.9(11); c = 1568.9(8) pm; β = 91.06(4)°. The compound forms a trimeric ion ensemble in which two of the lithium cations are coordinated by three nitrogen atoms of two phenylamidinate an ions, the other one by four nitrogen atoms of two chelating phenylaminidate anions and in addition by the nitrogen atom of a benzonitrile molecule.

Effect of a resonant medium on the polarization of a light pulse

The propagation of a 2π pulse in an ensemble of paramagnetic ions in a magnetic field is analyzed. The paramagnetic part of the magnetooptic activity of the medium contributes to the rotation of the polarization of the light pulse. The Faraday-rotation angle for a 2π pulse which has passed through the medium can be controlled by varying the saturation of the magnetic resonance.

Kinetic energy effects in an ion ensemble subjected to mass‐selective isolation and resonance excitation: A simulation study

AbstractA simulation study is described of the behaviour of ions confined in a quadrupole ion trap during each of two separate operations of a tandem mass spectrometric experiment. The two operations are those of mass‐selective ion isolation and mass‐selective resonance excitation to the point of ion ejection from the ion trap. The method of mass‐selective ion isolation simulated is that of consecutive ion isolation. Simulation data indicate that the collisional history of the ions prior to the isolation process can greatly influence the degree to which ions survive this process. Simulation data for mass‐selective resonance ejection are compared with experimental data obtained with a Finnigan‐MAT ion trap mass spectrometer. In each operation, the facility with which ions absorb energy from the field within the ion trap, whether this field is derived from the R.F. drive potential or a supplementary potential, can determine the extent to which ions are retained within the ion trap during the two mass‐selective operations described.

Collisional relaxation of vibrational excitation: Effects of bath gas structure

Infrared multiple photon dissociation has been used to study the relaxation of vibrationally excited trifluoroacetate anion. The internal energy of the ensemble of ions was monitored by measuring the extent of photodissociation in a Fourier-transform, ion cyclotron resonance spectrometer. Bimolecular quenching rate constants are measured in the presence of excess bath gases. Comparison of the experimental collision efficiencies with calculations of purely statistical energy redistribution has been done and indicates that species which can interact chemically with a trifluoroacetate anion exhibit a marked increase in the efficiency of collisional deactivation. Systematic use of the ratio R, defined as the average energy transferred per collision derived from experiment divided by the average energy transferred calculated from a statistical model, is proposed. A correlation of R with the hypothetical, limiting statistical lifetimes of the collision complexes is observed. This suggests that both the number and nature of oscillators of the bath gases as well as the intermolecular well depths with trifluoroacetate are important in determining the extent of energy transfer. It further suggests that energy transfer is limited by the collision duration.

A sensitive method for the detection of stored ions by resonant ejection using a wide-band signal

A new variant of resonance excitation of ions confined in a quadrupole ion trap has been presented. The first results obtained with this method were for N + 2 ions confined in the ion trap at the working point a z ≈ 0, q z 0.25. The ions are subjected to resonance radiation imposed in dipolar mode wherein a relatively wide band of some 50 frequencies, randomly chosen and with Δω 12.5 kHz, is swept slowly across the ion trap. When the properties of the entire ion ensemble are used, as is the case with the wide-band excitation, it is observed that minor frequency components of the spectrum of the ion motion are effectively quenched. Concomitantly, resonance absorption of wide-band excitation in the region of the fundamental axial secular frequency is enhanced by a factor in excess of 10 compared with monochromatic excitation. Absorption peaks obtained with wide-band excitation are quite simple and symmetric about the theoretical frequency in contrast with those obtained with monochromatic excitation which are complex in structure and markedly asymmetric.

Fast resonant nonradiative energy transfer in alexandrite

We measured the R-line fluorescence ( 2E → 4A 2) under site-selective dye laser excitation via pseudo-Stark R-line components in a modulated external electric field, and hence the kinetics of 2E-energy transfer among the Cr 3+ ions in mirror (C s) sites in alexandrite at T = 2 K were studied. Fast (microsecond range) resonant nonradiative 2E-energy transfer was observed. This shows that during the metastable 2E-state lifetime τ R = 2.4 ms the electronic 2E-excitations can perform many jumps over the Cr 3+(C s) ion ensemble. This result correlates directly with the results of four-wave mixing experiments [1,2], indicating the existence of long-range spatial diffusion of 2E excitation among the Cr 3+ (C s) ions.

Laboratory-frame and rotating-frame ion trajectories in ion cyclotron resonance mass spectrometry

The magnitude of the ion cyclotron resonance (ICR) time-domain signal detected from the oscillating differential charge induced on opposed detector electrodes depends on the number, ICR orbital and magnetron radii, and phase coherence of the trapped ions. In this paper, we present analytical solutions for the motion of magnetically confined ions of arbitrary initial position, velocity and phase during and after excitation by a spatially uniform oscillatory electric field. Resonant and non-resonant single-frequency and frequency-sweep (chirp) excitation are treated. Spatial coherence may then be incorporated by analyzing the ion ensemble into ion packets, such that ions in each packet share a common ICR orbit center. We find that resonant (single-frequency or frequency-sweep) electric field excitation not only increases the ICR orbital radius, but also induces an oscillating (for linearly polarized excitation) or rotating (for circularly polarized excitation) shift in the center of the ion cyclotron orbit of the ion packet (i.e. the magnetron radius). The amplitude of the r.f.-induced oscillating or rotating magnetron radius increases directly with ion mass-to-charge ratio and r.f. electric field amplitude. Optimal excitation for high mass ions should therefore be conducted with low magnitude long-duration excitation rather than a short high magnitude “rectangular” (or “burst” or “impulse”) waveform. None of the above excitation waveforms changes the initial spatial distribution of the ion packet: in particular, off-resonance single-frequency excitation results in oscillatory variation in ICR orbital radius, but does not induce any net spatial synchronization in the ion packet. Finally, ion trajectories during on- and off-resonance single-frequency excitation are displayed in the usual fixed laboratory coordinate frame as well as in a coordinate frame rotating about the z-axis at the ICR orbital frequency of that ion. Phase coherence and shifts in the center of the ICR orbit are much more easily visualized in the new rotating-frame representation.

Phase synchronization of an ion ensemble by frequency sweep excitation in Fourier transform ion cyclotron resonance.

The Fourier transform ion cyclotron resonance (FT-ICR) signal is produced by the coherent motion of a population of ions. The ability to produce a well-defined ion packet by excitation of an initially random ion ensemble is a major limiting factor of high mass FT-ICR. Ions must be both resonant and in phase with the applied radio frequency excitation field to be accelerated to radii suitable for detection by FT-ICR. Synchronization of the phase angles of an ensemble of ions occurs by off-resonant acceleration during frequency swept excitation. Results from computer-simulated ion trajectories suggest that phase synchronization of the ion packet prior to resonant excitation results in better spatial definition of the ion ensemble.

Ion detection by Fourier transform ion cyclotron resonance: the effect of initial radial velocity on the coherent ion packet.

Ion detection by Fourier transform ion cyclotron resonance (FT-ICR) is accomplished by observing a coherent ion packet produced from an initially random ensemble of ions. The coherent packet is formed by excitation with a resonant oscillating electric field. Ions that are out of phase with the applied radio frequency (rf) electric field experience a continuous misalignment of the electric field vector. The misalignment creates a net force of the electric field perpendicular to ion motion. The perpendicular component of the rf electric field creates a frequency shift resulting in phase synchronization of the ion ensemble. The phase coherence of the ion packet affects both the sensitivity and the resolution of FT-ICR.

Line shape of three-level ions in Paul traps.

A cloud of three-level ions (${\mathrm{Ba}}^{+}$) confined in a Paul trap was illuminated with two lasers and the resulting fluorescence was observed as a function of the laser detunings from the ionic resonance. The observed spectra show features due to the oscillatory motion of the trapped ions. In order to describe the observed line shapes, calculations are presented in which the ion ensemble is separated in classes of velocity amplitudes of the oscillatory motion rather than velocity classes.

ChemInform Abstract: Recent Advances in the Theory of the Electric Double Layer

Recent progress in the theory of the electric double layer at a metal/solution interface is reviewed. In the absence of specific adsorption the system may be represented as jellium in contact with an ensemble of hard sphere ions and dipoles; results of explicit model calculations are compared with experimental data. When ions are specifically adsorbed, the induced change in the surface dipole potential is of particular interest. Due to the effective screening of the adsorbate charge by the solvent and by the metal electrons, the corresponding dipole moments are relatively small. Finally, isotherms for ionic adsorption are considered in the limit of vanishing bulk concentration.