Calculation by plane wave Born approximations of electron-impact ionization of silver and copper

The plane wave Born approximation is used to calculate total electron impact ionization cross section of silver and copper. Wavefunctions of the target and residual ions were modeled by non orthogonal Hartree-Fock and Dirac-Fock orbitals. The wave functions of the atom and residual ion are calculated with allowance for relaxation effects. The one-electron wavefunction of the continuous spectrum for the ejected electron is obtained using single-configuration Hartree-Fock and Dirac-Fock method. The orthogonalization of the ejected electron wave functions to all occupied orbitals of the target atom is performed. Results of calculations are compared to available experimental measurements and theoretical calculations performed by non relativistic one-electron PWBA, where the ejected electrons is modeled by the hydrogenic Coulomb wave function.     

Electron impact ionization of diatomic molecules

Cross sections for the ionization of N₂, CO and O₂ diatomic molecules by electron impact are calculated. The applied distorted wave model is based on our previous studies for positron impact, the molecular orbitals being described by Gaussian wavefunctions. Our study emphasizes the importance of electron exchange and of using correct distorted waves for the ejected electron.     

L-shell ionization in proton-atom collisions

The cross section of ionization of atoms by protons is calculated in the plane-wave approximation. It is shown that the wave function of the ejected electron must be orthogonal to all wave functions of the atom. A method taking into account a finite number of wave functions in the calculation of the ionization amplitude is proposed. The calculated cross sections of ionization of nitrogen, oxygen, and neon atoms by protons agree well with the experimental data and results of calculations carried out by other authors.     

Laser-assisted positron-impact ionization of atomic hydrogen

We study the ionization of atomic hydrogen by a fast positron in the presence of an external linearly polarized laser field. We concentrate on the limit of a small momentum transfer and describe the fast positron's continuum states by Volkov wave functions. The ejected electron is described by a Coulomb-Volkov wave function. We are limited to small laser intensities such that the dressed state of the target is treatable within the time-dependent perturbation theory, even though the laser intensity is still quite high by laboratory standards. Numerical results for the triply differential cross sections and their dependencies on laser-field parameters are discussed and compared with the results of laser-assisted ionization by electron impact.     

Ionization of diatomic molecules by electron impact

An analytical expression for the amplitude of ionization of the hydrogen molecule by electron impact in the first Born approximation with a one-center Coulomb continuum wave function is derived. The case where the incident electron energy is much greater than the ejected electron energy is considered. The molecular wave functions were constructed in the approximation of linear combination of atomic orbitals with overlapping configurations. The role of the orthogonalization of the initial and final wave functions of the active electron of the target is elucidated. The triple differential ionization cross sections for the different orientations of the molecular axis and that averaged over all orientations are calculated. The secondary electron angular distribution is represented in the form of three-dimensional images. A comparison with the results of other theoretical calculations and experimental data is performed.     

Ultrafast electronuclear dynamics of H(2) double ionization

The ultrafast electronic and nuclear dynamics of H(2) laser-induced double ionization is studied using a time-dependent wave packet approach that goes beyond the fixed nuclei approximation. The double ionization pathways are analyzed by following the evolution of the total wave function during and after the pulse. The rescattering of the first ionized electron produces a coherent superposition of excited molecular states which presents a pronounced transient H(+)H(-) character. This attosecond excitation is followed by field-induced double ionization and by the formation of short-lived autoionizing states which decay via double ionization. These two double ionization mechanisms may be identified by their signatures imprinted in the kinetic-energy distribution of the ejected protons.     

Relative phase measurement of a stark wave packet in the vicinity of the saddle point

A gas of Rb atoms in a static electric field has been photoexcited to just above the classical ionization threshold by a phase-locked sequence of two far infrared pulses. A single laser pulse generates a series of ejected electron packets emerging at the saddle point of the potential; each of the ejected packets is characterized by a phase and a chirp. We calculate and measure these phases and chirps using the time dependent interference of the electronic wave function controlled by the delay between the two light pulses.     

Double photoionization and transfer ionization of he: shakeoff theory revisited

The shakeoff theory of Aberg [Phys. Rev. A 2, 1726 (1970)] is revisited. With the sudden approximation, we calculate the shakeoff probability when one of the electrons in He is ejected with a finite velocity. This theory is used to examine ratios of cross sections for double to single photoionization and transfer ionization to single electron capture. It is also shown that the momentum distribution of the shakeoff electron provides a means to measure the correlation of the ground state wave function directly.     

Quasi-binary incident electron—centre of mass collision in (e, 3e) process on He and He-like ions

We present in this communication the results of our first Born calculation in the three-Coulomb (3C) wave approach for the (e, 3e) process on He and He-like ions at an incident electron energy 5599 eV in the coplanar constant θ12 as well as out-of-plane constant φ12 modes. These two geometrical modes are such that the quasi-binary collision between the incident electron and centre of mass of the ejected electrons is in the scattering plane. The theoretical formalism has been developed using plane waves, Le Sech wave function and approximated BBK-type wave function respectively for the incident and scattered, bound and ejected electrons to calculate five-fold differential crosssection (FDCS) of the (e, 3e) process. We emphasize on the similarities and dissimilarities (asymmetries) in the angular profile of the FDCS in two modes as well as the effects of post-collision interaction (between the ejected electrons) and nuclear chargeZ on the angular profile of the FDCS. We observe that with the increment of nuclear charge the two quasi-binary collisions approach towards identical behaviour at larger mutual angles and thus bringing less asymmetry in FDCS for higherZ target.     

Waves in plasma formed by above-threshold ionization of gas atoms

In the regime of above-threshold ionization of gas atom in the field of laser radiation, plasma with photoelectron distribution consisting of peaks at discrete energy values is formed. It is shown that the number of longitudinal waves in such plasma coincides with the number of peaks in the distribution function. When peaks practically don't overlap, the dispersion law of each wave in the region of short waves is determined by electrons from the corresponding peak. In this case the phase and group velocities of the waves are close to the electron velocity, which corresponds to the peak maximum. It is possible to talk about such waves as an electronic sound, since the perturbations of the electron density mainly arise due to pressure perturbations. When the peaks are narrow, but having a finite width, the Cherenkov damping of waves is exponentially small. Numerical calculations the dispersion laws for of the two and four waves in photoionized xenon plasma, in which the electron distribution function consists of two or four narrow peaks are given.     

A solution of the Pekarek-Krejci equation for ionization waves

The Pekarek-Krejci equation for ionization waves is solved for sinusoidal variations. The different wave types are examined when the phase angle between the electron temperature and electron density is varied.     

Scaling of cross-sections for asymmetric (e, 3e) process on helium-like ions by fast electrons

An approximate simple scaling law is obtained for asymmetric (e, 3e) process on helium-like ions for double ionization by fast electrons. It is based on the equation (Z ^′3π) exp[-Z(r₁ + r₂)],Z′ = Z – (5/16) for ground state wave function of helium-like ions and Z^′2 scaling of energies. The scaling law is found to work very well if the lower energy electron is ejected along the momentum transfer direction and the other one is ejected in the opposite direction. It also works quite well if this electron is ejected within about 90° of the momentum transfer direction with the other electron going in the opposite direction. The scaling law becomes increasingly accurate as the target nuclear charge and the energy increase.     

Magnetically quantized continuum distorted waves

A new derivation of continuum distorted-wave theory is presented. It is generalized to magnetically quantized continuum distorted waves. The context is analytic continuation of hydrogenic-state wave functions from below to above threshold, using parabolic coordinates and quantum numbers including m the magnetic quantum number. This continuation applies to excitation, charge transfer, ionization, and double and hybrid events for both light- and heavy-particle collisions. It is applied to the calculation of double-differential cross sections for the single ionization of the hydrogen atom and for a hydrogen molecule by a proton for electrons ejected in the forward direction at a collision energy of 50 keV and 100 keV respectively.     

(e, 3e) test on e-e correlations in helium

The angular variations of the five-fold differential cross section obtained by using different wave functions of helium are compared with experimental data. It is found that in the coplanar geometry two kinematical arrangements, (i) equal energy sharing between the two ejected electrons with one of them ejected along the momentum transfer direction and the other along varying direction and (ii) the Bethe ridge condition with fixed sum of ejected electron energies and varying angle between them, are very sensitive to e-e correlations contained in the target wave function. This comparison has been used to show that open-shell class of wave functions better incorporate e-e correlations than the closed-shell class.     

氦原子(e,2e)反应中库仑波描述入射电子的理论研究

在前期工作的基础上,当初通道使用具有有效电荷库仑波时,完成了电子入射离化氦原子三重微分截面的理论推导.计算表明:初通道库仑场对较低入射能量情况下,(e,2e)过程的三重微分截面有较大影响.     

Si2+离子与氢原子碰撞电离过程的CTMC计算

应用经典径迹蒙特卡罗方法研究Si²⁺离子与氢原子碰撞电离反应过程.计算了随 入射离子能量变化的总截面、出射电子随角度和能量变化的一阶、二阶微分截面,及出射电子随 入射离子能量变化的平均能量.根据计算结果,讨论展示了软碰撞、电子转移到入射离子连 续态、两体相遇碰撞等电离机理,阐明了它们对碰撞总截面、微分截面、电离电子能量的影 响.通过计算出射电子到入射离子和靶的距离比的电离电子数分布研究了不同入射离子能量 “鞍点”电离机理的可能性. 关键词： 重粒子碰撞过程 经典径迹蒙特卡罗方法 电离机理     

Näherungsformeln für den Ionisierungsquerschnitt derK-Schale durch Elektronenstoß

Burhop's non relativistic result for the ionization cross section of theK-shell was recalculated. The remaining integrations over the change of momentum and the momentum of the ejected electron were done numerically especially for elements of low atomic number. The ionization function of the various elements normalized to unity at the maximum shows very small variation with atomic number. This universal behaviour of the ionization function was used to construct simple approximation formulae.     

Energy spectrum of ejected electrons in ionization of hydrogen atoms by electrons

Energy spectrum of ejected electrons in ionization of hydrogen atoms has been calculated following a multiple scattering theory of Das and Seal [15]. The results show peaks around two to three Rydbergs of energies of the ejected electrons, for incident electron energy of 250 eV and 500 eV, considered here, and for different combinations of the angular variables of the scattered and the ejected electrons, for scattering in a plane. The peaks are very similar to those observed in relativistic K-shell ionization of Ag atoms by electrons at 500 KeV energy [6]. The physical origin of these peaks may be traced to the second order scatterings, scattering first by the atomic nucleus (or the atomic electron) and then a second time by the atomic electron. These peaks are, however, absent in the first Born results. Experimental verification of the present results and theoretical calculation by some other well-known methods will be interesting.     

Photodetachment microscopy of

Photodetachment of ions is performed in the presence of a static electric field. A high spatial resolution electron detector is used to map out the ejected electron's wave function. Propagation over half a metre does not alter the stationary structure the electron wave possesses in the direction orthogonal to the detachment motion. Nodes and antinodes of electron current density are observed, that can be interpreted as direct imaging of the internal atomic wave function. Because detachment of a negative ion can be represented accurately in the free-electron approximation, the obtained images can also be viewed as direct experimental representations of the Green function of the uniform acceleration problem. Agreement of the measured distributions with the exact expression of this wave-function appears quite satisfactory. Received: 5 June 1998 / Accepted: 16 October 1998     

ELECTRON MOMENTUM SPECTRA OF EXCITED He(2~1S) AND He(2~3S)

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