Multiple Ionization Of Atoms Research Articles

Frustrated double ionization of argon atoms in strong laser fields

This works shows a new approach to study the electron recapture process during double and multiple ionization of atoms. This scheme is applicable to non-dissociative processes in molecules, which are not accessible with existing methods based on the measurement of kinetic energy released from fragmentation processes. The experiments show a transition of frustrated double ionization in argon from a non-sequential scenario to a sequential scenario.

Multiple ionization of atoms by highly charged ions

A method is suggested for quickly and easily estimating multiple ionization (MI) cross sections of heavy atoms colliding with highly charged ions, using the independent-particle model (IPM). One-electron ionization probabilities p(b) are calculated using the geometrical model for values at zero impact parameter b and the relativistic Born approximation for one-electron ionization cross sections. Numerical results of MI cross sections are presented for Ne and Ar atoms colliding with Ar8+, Fe20+, Au24+, Bi67+ and U90+ ions at energies 1 MeV u–10 GeV uand compared with available experimental data and CTMC (classical trajectory Monte Carlo) calculations. The present method of calculation describes experimental dependencies of MI cross sections on the number of ejected electrons m within a factor of two to three. Numerical calculations show that at intermediate ion energies E = 1 − 10 MeV u, the contribution of MI cross sections to the total, i.e. summed over all m values, is quite large ∼35% and decreases with increasing energy.

Multiple ionization of atoms and molecules impacted by very high-q fast projectiles in the strong coupling regime (q/v > 1)

In this paper, we present a simple theoretical approach to calculate the multiple ionization of big atoms and molecules induced by very high-q fast projectiles in a strong coupling regime (q/v > 1). The results obtained from this approach are in excellent agreement with the available experimental data. A probable scenario of molecular multiple ionization by fast and very high-q projectiles is discussed. The very small computational time required here and the good agreement with the existing experimental data make it a good candidate for studying the multiple ionization of complex molecules under high linear energy transfers.

Electron-impact ionization of atomic hydrogen: dynamical variational treatment

A simple and straightforward calculating scheme is proposed for electron-impact single and multiple ionization of atoms. The method is based on the application of the Hulthen-Kohn dynamical variational principle. An effective charge seen by the scattered electron is determined for a certain type of trial wave functions mathematically in a rigorous way excluding any empirical assumptions. Validity of the elaborated approach is assessed by calculating triply differential cross section (TDCS) for electron-impact ionization of hydrogen. It is shown that, inclusion of the effective charge into the calculation reduces height of a “binary peak” in comparison with the first Born approximation result. The height of a “recoil peak” depends on the sign of the effective charge. The calculated TDCS are compared with the available experimental data and with the results of sophisticated theories and agreement is found.

Multiple ionization of atoms with xuv attosecond pulses: Two-photon double ionization of helium with 50 eV photons

We consider two-photon double ionization of helium by two xuv photons in the region around the sequential ionization threshold. We show that, on the attosecond timescale, the mechanism for double ionization is dominated by the absorption of one photon by each electron in the fundamental state He(1s2). We examine the dynamics of two-photon double ionization of helium for an averaged photon energy ω = 50 eV, with a pulse duration of two optical cycles. The double ionization rate, energy and angular distributions are calculated by solving the time-dependent Schrödinger equation. Results are discussed on the basis of a model.

New positron sources using a 1.7 MV tandem and a RDS-112 cyclotron accelerators

In this paper we give a brief overview of the recent results on the single and multiple ionization of atoms by positron impact. In addition, the future plans of new alternative intense positron sources based on using either the 1.7MV tandem accelerator or the cyclotron RDS-111 accelerator are described for atomic and molecular studies.

Multiple fragmentation of atoms in femtosecond laser pulses

Multiple ionization of atoms by an ultrashort intense laser pulse is a process in which the few-body problem is closely interrelated with the highly nonlinear interaction between the electrons and the external field. We review recent advances in unveiling the mechanisms behind the unusually large ion yields for double and multiple ionization observed in a strong laser pulse. Its study requires on one hand the combination of highly differential experimental techniques with laser systems having high repetition rates and on the other the development of new theoretical methods to simultaneously account for the long-ranged Coulomb interaction between the particles and the field nonlinearity. Different mechanisms are analysed diagrammatically and quantitatively in comparison with experimental data for the total ion yields. Distributions for the electron and ion momenta of coincidence measurements are discussed along with predictions of the various theoretical methods.

Measurement of the mean transverse kinetic energy of recoil ions produced inenergetic electron–atom collisions

A realistic approach for determining the mean transverse kinetic energy (MTKE)of recoil ions produced in energetic electron–atom collisions from the knowledge offull width at half maximum of the ion peaks has been described and discussed.The method is independent of any critical assumption and requires only the inputvalues of ‘optimized parameters’ of the time-of-flight mass spectrometer employedfor detecting the recoil ions. The method has been used to calculate the MTKE ofargon recoil ions produced in 24 keV e− – Arcollisions. The results obtained are compared with those determinedfrom a relation given by Olson (Olson R E 1979 J. Phys. B: At.Mol. Phys. 12 1843); the agreement between the two results is foundto be reasonably good within the experimental uncertainty of themeasurements. Further, from dependences of MTKE on charge state fractionsFr of recoil ions andon their charge states q,it is found that Frvaries with qas 1/q4for multiple ionization of atoms by impact of energetic electrons, unlike as1/q2for multiple ionization of atoms by impact of energetic highly charged heavy ions.

Single and Multiple Ionization of Atoms by Electron Impact

AbstractWe report progress achieved during decades on direct single and multiple ionization of simple atoms by electron collsion. In particular we investigate total cross sections from thresh old to high energies. We show that all experimental data compare favorably with Wannier thresh old theory. A better understanding of the ionization process one gets from the analysis of multiply differential cross sections. To this end we discuss (e, 2e) and (e, 3e) events.

Ionization of an atom by photoabsorption at high photon energies: unified view in terms of singularities of the Coulombic potentials

We discuss a unified nonrelativistic approach to single and multiple ionization of atoms by absorption of a photon of high incident energy ω (but still ω⪡ m). The approach is based on asymptotic Fourier transform theory (AFT), modified by Coulombic interactions. The AFT theory connects the high energy behavior of photoabsorption matrix elements with the singularity structures of the inter-particle Coulomb interactions and takes into account initial and final state correlation. The modification of this AFT result by Coulombic interactions leads to a rapid convergence of cross sections with photon energy. We illustrate these ideas for the simple example of photoionization in a potential and then discuss its generalizations.

Signatures of Electron–Electron Interaction in Fast Highly Charged Ion–Atom Collisions

We report on calculations of differential electron spectra for double ionization of helium by fast highly charged ion impact based on a first order Born (shake-off) model. These spectra are shown to be very sensitive to the electron–electron interaction. The potential of recoil ion momentum spectroscopy for investigating the correlated dynamics of electrons in multiple ionization of atoms by fast heavy ion impact is discussed.

Fermion molecular dynamics in atomic, molecular, and optical physics

Classical dynamics, often called 'molecular dynamics' when applied to atoms and molecules, is much easier than solving the many-body Schrodinger equation for a number of reasons. In particular, correlation and rearrangement are simple in classical dynamics. Fermion molecular dynamics (FMD) is a quasi-classical method for treating quantum-mechanical systems using classical equations of motion with momentum-dependent model potentials added to the usual Hamiltonian. These model potentials constrain the motion to satisfy the Heisenberg uncertainty and the Pauli exclusion principles. We discuss the foundations of the FMD model and its applications to atomic and molecular structure, ion-atom collisions, stopping powers, formation of antiprotonic atoms, and multiple ionization of atoms in strong laser fields.

Multiple ionization of atoms and molecules in collisions with fast ions. II. Ion-molecule collisions

An extended version of the statistical energy-deposition model is used for a description of multiple ionization of molecules by energetic ion impact. The energy transferred to the molecule during the collision is calculated as a function of the impact parameter within the local-electron-density approximation for a fixed molecular orientation. The fluctuating character of the deposited energy is taken into account by introducing a straggling of the energy transfer. For a given deposited energy the probability of multiple ionization of the molecule is assumed to be proportional to the volume of phase space available at the considered ionization state. The total ionization cross section is obtained by integrating over impact parameters and averaging over all orientations of the molecule. Sample calculations for collisions of He and F ions with N${}_{2}$ and CO molecules are presented and compared with experimental data. A dependence of the multiple ionization cross section on the molecular orientation is considered. A strong molecule alignment effect has been obtained in agreement with recent experimental findings.

Multiple ionization of atoms and the energy of recoil ions in collisions with fast, multiply charged ions

On the basis of the sudden perturbation approximation and the model of independent electrons, simple analytical expressions are obtained for the cross sections of multiple ionization of atoms and the average energies of recoil ions in collisions between atoms and fast, multiply charged ions in the range of parameters in which the Born approximation is inapplicable. An expression for the energy distribution function of recoil ions is also obtained.

Appearance intensities for multiply charged ions in a strong laser field.

We study multiple ionization of atoms by a strong laser field using a time-dependent approach based on the Thomas-Fermi model. The evolution of the electron density under the influence of a transient, linearly polarized radiation field is determined by numerical solution of hydrodynamic equations on a two-dimensional grid. We find a threshold ``appearance intensity'' for a given charge state, i.e., the laser intensity at which such a charge state first appears, which is in reasonable agreement with experimental results for high charge states.

Multiple-charged secondary-ion emission from silicon and silicon oxide bombarded by heavy ions at energies of 0.4-10 MeV.

Secondary-ion yields have been measured for Si and SiO[sub 2] targets bombarded by C, Si, Ge, and Ag projectiles over an energy range beween 0.4 and 10 MeV, where the atomic-collision process changes from a nuclear to an electronic one. Obtained yields of secondary Si[sup [ital q]+] ([ital q]=1,2,3,4) ions for the C projectiles are generally decreasing functions of incident energy. On the other hand, the yields for Ag increase with increasing energy except for Si[sup +]. The possibility of multiple-charged recoil-ion production through the simultaneous process of ionization and recoil caused by the projectiles is discussed on the basis of an independent-electron model, which describes multiple ionization of atoms by energetic heavy-ion impact.

Multiple ionization of atoms by powerful circularly polarized laser field.

We present a theoretical description of the multiple ionization of atoms by a poweful circularly polarized laser field. Our calculations are based on the statistical model of the atom. The modified Thomas-Fermi equation in the rotating frame has been derived. Appearance intensities versus laser frequency have been plotted and discussed. The instability of the solution for circularly polarized laser light of sufficiently high frequency is expected.

Implications of electron correlations for multiphoton excitation

Doubly excited states of atoms display strong electron correlations, particularly with increasing excitation and in the vicinity of the double-ionization limit. We discuss the nature of these correlations and the attendant implications for multiphoton excitation of such states. Questions discussed include favored and unfavored pathways of excitation and whether multiphoton multiple ionization of atoms proceeds through a sequential ejection of the electrons or through a direct simultaneous ejection into the multielectron continuum.

Defect formation in solids by decay of electronic excitations

We consider a new type of nonradiative transitions in nonmetallic solids. The transitions are not accompanied by heat release but by large (compared with interatomic distances) displacements of individual atoms. These instabilities (electrostatic, vibronic, structural), which lead to formation of defects in solid crystals and glasses, are classified. We describe defect-formation processes both in ionic crystals upon decay of self-trapping excitons, and in semiconductors following multiple ionization of atoms near pre-existing charged impurity centers. The mechanisms whereby complex defects are restructured in semiconductors when nonequilibrium current carriers are introduced and when electrons and holes recombine are discussed. The role of current carriers in thermal production of defects is considered. The mechanism of formation of peculiar defects in glassy semiconductors is discussed.

LVIII.On the absorption of x-rays and multiple ionization of atoms

LVIII.<i>On the absorption of x-rays and multiple ionization of atoms</i>