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.     

Semiempirical model description of the low energy electron scattering from helium

The simple model introduced by Schrader to study positron-atom interactions is employed in the case of electron-helium elastic scattering. It is found that when combined with the AAFEGE exchange potential this model can provide quite satisfactory differential and total cross sections for impact energies larger than 3eV.     

Multiple scattering versus superstructures in low energy electron diffraction

LEED patterns indicating a long periodicity of the surface layer are discussed in terms of double scattering between short-period structures occurring in the bulk. It is shown that the geometry of the diffraction pattern does not permit a distinction between a true twodimensional superstructure and superposed two- or three-dimensional structures (“pseudosuperstructure”) giving rise to the same lateral periodicity as the superstructure. Several examples for such pseudosuperstructures are given.     

Intermediate changes in high energy elastic scattering from atoms

Correction of the Glaubner T-matrix to account for target particle motion and energy change in elastic scattering of charged particles from atomic systems is found to vanish to leading order.     

Excitation of adsorbed molecule vibrations in low energy electron scattering

We develop a theory of low energy electron loss spectroscopy of vibrational modes of molecules adsorbed on metal surfaces. Differential and total cross sections are calculated in the Distorted Wave Born Approximation, assuming i) strong elastic scattering on the metal surface, ii) direct electron-molecule interaction via the electric dipole field associated with the molecular vibration. The angular distributions are calculated and discussed for molecules adsorbed at various distances above the metal surface and for several electron energies and impact angles. The influence of electronic screening of dipolar oscillations is discussed and the consequences of the classical induced image dipoles are explored. It is shown that the metal surface selection rule known in IR spectroscopy is only approximately valid in electron scattering. Finally, we give numerical estimates of the inelastic scattering cross sections for the stretching vibrations of CO molecule adsorbed on transition metal surfaces, in reasonable agreement with experiments.     

Low energy positron scattering from atoms in and on solids observed with low energy positron diffraction and reemission microscopy

The present status of low energy positron diffraction (LEPD) and positron reemission microscopy (PRM) is reviewed in the context of unanswered questions regarding the elastic scattering of positrons in the 1–300 eV energy range from atoms in solids and at solid surfaces. Recent LEPD studies yield an agreement between theoretical and experimental diffraction intensities for semiconductors that has never been equalled in electron diffraction studies. This situation is discussed in terms of the repulsive interaction between the positron and the embedded atomic potential and the lack of exchange with the nonspherically distributed valence electrons. The scattering of re-emitted positrons in PRM from atoms chemisorbed or physisorbed on the re-emitting surface has not yet received the same theoretical attention as scattering from embedded atoms in LEPD. Possible ways in which positron scattering from overlying atomic structures manifests itself in PRM as well as positron re-emission holography are discussed, both from the practical viewpoint of observing these structures and in the context of fundamental questions regarding the positron re-emission process itself.     

Elastic electron scattering by mercury atoms

Zeitschrift für Physik A Hadrons and nuclei - The cross section and Mott asymmetry function of elastic electron scattering by mercury atoms have been calculated for energies of 46, 79, 100,...     

Second order density effects in low energy pion scattering

The differences between a full Lorentz-Lorenz potential modification and a ?² approximation are examined for low energy pion-nucleus elastic scattering. It is found that the two methods give comparable results when Coulomb, absorption and kinematic effects are taken into account.     

Comments on Lorentz-Lorenz effects in low energy pion scattering

The differences between a full Lorentz-Lorenz potential modification, and a ?² approximation to this modification are examined for low energy pion-nucleus elastic scattering. The relationship between these approaches and the single-scattering impulse approximation is also investigated.     

Differential cross section surfaces for low energy scattering of electrons and positrons from rare gas atoms

The differential cross sections for scattering of electrons and positrons from He, Ne, Ar, Kr, and Xe at projectile energies below the inelastic thresholds are calculated using a model potential approach in which the interaction between the projectile and the target atom is partitioned into static, exchange (for electrons), and correlation-polarization parts. Two different forms of the parameter-free correlation-polarization potential are suggested; in both cases the correlation-polarization potential is determined by smoothly matching the asymptotic form of the polarization potential (1/r ⁴) to the correlation potential at the outermost orbital radius of the target atom. The results of angular distributions are presented in the form of contours of constant differential cross sections as well as in the form of differential cross section surfaces in three-dimensional plots. Both of these presentations display the locations of the principal maxima and minima of the differential cross sections as well as the critical points in a very useful manner.     

Polarization and exchange effects in elastic scattering of electron with atoms and ions

Laser-induced electron diffraction(LIED), in which elastic scattering of the returning electron with the parent ion takes place, has been used to extract atomic potential and image molecular structures with sub-?A precision and exposure time of a few femtoseconds. So far, the polarization and exchange effects have not been taken into account in the theoretical calculation of differential cross section(DCS) for the laser-induced rescattering processes. However, the validity of this theoretical treatment has never been verified. In this work, we investigate the polarization and exchange effects on electron impact elastic scattering with rare gas atoms and ions. It is found that, while the exchange effect generally plays a more important role than the polarization effect in the elastic scattering process, the exchange effect is less important on electron–ion collisions than on electron–atom collisions, especially for scattering in backward direction. In addition, our calculations show that, for electron–atom collisions at incident energies above 50 e V, both the polarization and exchange effects can be safely neglected, while for electron–ion collisions, both the polarization and exchange potentials do not make substantial contributions to the DCS at incident energies above 20 e V and scattering angles larger than 90?. Our investigation confirms the validity of the current LIED method.     

Relativistic corrections to electron scattering: (II). Inelastic scattering

Relativistic corrections to inelastic electron scattering have been investigated using the results of a previous calculation on elastic scattering. A detailed discussion is made of the kinematics of inelastic scattering. Excitation of discrete states is treated in detail by two different methods, with particular attention paid to kinematical factors. Deuteron breakup is discussed and treated in a very similar manner to the discrete excitations. Comparison is made with analyses using plane wave final states and with previous work.     

Superelastic electron scattering by metastable strontium atoms

Superelastic electron scattering by metastable strontium atoms is experimentally studied using intersecting electron and atomic beams and an electron spectrometer. The energy dependence of the effective cross section of superelastic electron scattering in the energy range 0.15–2.0 eV has been obtained for the first time.     

Analytical independent-particle model for electron scattering by argon at low energy

The analytical independent-particle model of Berg, Purcell, and Green (BPG) is extended to describe low-energy scattering of electrons by the argon atom. The Ramsauer-Townsend minimum and the scattering length are only well reproduced when the BPG model is supplemented with a polarization potential as proposed by Sandhas.Dedicated to Prof. Werner Sandhas on the occasion of his 60th birthday     

低能电子散射诱导荧光研究装置的设计

完成了低能电子散射导致的分子及其解离碎片的荧光研究装置的设计。此装置可用于研究荧光寿命、激发函数、电子能量损失谱和分子解离过程。与其它国外研究装置相比,该装置具有综合性并增加了平行板能量分析器,因而拓宽了该类装置的研究范围。     

Correlation and finite interaction-range effects in high energy electron inclusive scattering

We calculate cross sections of high energy electron inclusive scattering off nuclear matter in a new and consistent formulation based on the Glauber approximation. It allows us to examine the details of the nucleon-nucleon interaction in the final-state interaction and the nuclear wave function. We point out the importance of the finite-range effect and of the nuclear short-range correlations.     

The impact of vibrational wave function on low energy electron vibrational scattering from nitrogen molecule

The vibrational wave function of the target theoretically plays an important role in the calculation of vibrational excitation cross sections. By a careful study of the differential cross sections resulting from different vibrational wave functions we find that cross sections are susceptible to vibrational wave functions. Minor changes in the vibration wave function may cause a significant change in the cross section. Even more surprising is that by selecting a few numbers of potential models(which determine the vibrational wave functions) we can often calculate the differential scattering cross section in much closer agreement with experiment in the framework of body-frame vibrational close-coupling theory, which suggest that an accurate potential energy may play a more important role in scattering than we thought before.     

入射电子被中性原子散射过程中的库仑波描述

在前期工作的基础上,给出了有效电荷Zeff的解析形式.研究发现:有效电荷Zeff与入射电子的能量和散射角有关.我们早期工作的一个重要缺陷是:对于初、末通道,分别使用了解析的平面波和库仑波,而现有的波函数与早期工作之间的一个重要差别在于:在初通道,现有的波函数包含有入射电子与中性原子之间的短程相互作用效应,而早期文章则没有这种效应.这里使用的末态波函数与以前是相同的.当入射电子处在有效电荷库仑场的情形下,我们计算了电子入射离化氦原子的三重微分截面,并发现现有的理论计算与实验结果很好的一致.