Full Second-Order Distorted-Wave Calculation without Approximations for Atomic Excitation by Electron Impact

A new technique has been developed for evaluating second-order distorted-wave amplitudes for atomic excitation without making any approximations. By this technique, second-order amplitudes with arbitrary distorted waves and arbitrary Green\u27s functions in the interaction can be evaluated with comparable difficulty. The utility of the method is demonstrated through a practical calculation of the second-order distorted-wave approximation for electron excitation of the 2p state of hydrogen

Multicenter Distorted-Wave Approach for Electron-Impact Ionization of Molecules

We have previously used the molecular three-body distorted-wave model to examine electron-impact single ionization of molecules. One of the possible weaknesses of this approach lies in the fact that the continuum electron wave functions do not depend on the orientation of the molecule. Here we introduce a model called the multicenter molecular three-body distorted-wave (MCM3DW) approach, for which the continuum electron wave functions depend on the orientation of the molecule at the time of ionization. The MCM3DW results are compared with experimental data taken from work by Dorn and colleagues [Ren, Phys. Rev. A 91, 032707 (2015)10.1103/PhysRevA.91.032707; Phys. Rev. A 93, 062704 (2016)10.1103/PhysRevA.93.062704; Phys. Rev. A 95, 022701 (2017)10.1103/PhysRevA.95.022701; Phys. Rev. Lett. 109, 123202 (2012)10.1103/PhysRevLett.109.123202; Gong, Phys. Rev. A 98, 042710 (2018)10.1103/PhysRevA.98.042710] in which they measured triple differential cross sections for single ionization of molecular hydrogen while simultaneously determining the orientation of the H2+ ion at the time of ionization. Comparisons are also made with previous theoretical calculations. It is found that orientation effects are important for low incident energy electrons. Very nice agreement with experiment and the time-dependent close coupling results is found for an incident electron energy of 26 eV. Orientation effects become relatively unimportant by the time the incident electron energy is 54 eV

Connection between Superelastic and Inelastic Electron-Atom Collisions Involving Polarized Collision Partners

It is shown how the results of a recent experiment by Jiang, Zuo, Vuković, and Bederson [Phys. Rev. Lett. 68, 915 (1992)], who investigated low-energy electron scattering from laser-excited polarized sodium atoms in the initial (3p) 2P°3/2 (F=3, MF=3) state, can be related to the inelastic 3S→3P transition involving initially unpolarized electron and atom beams. Hence, this method can provide an independent check of the traditional electron-scattering experiment with unpolarized beams

Doubly Differential Cross Sections for Proton-Impact Ionization of Argon

Proton-impact-ionization cross sections for argon which are differential in the energy and angle of the ejected electron have been calculated within the framework of the Born approximation using both Hartree-Slater and Hartree-Fock wave functions for the ejected electron. Results of the two types of calculations are compared with each other and with experiment. Differential cross sections for all five sub shells of argon are examined and particular attention is given to some interesting features of the K-shell cross sections. The range of applicability of the theoretical models is discussed

Effect of Polarization and Absorption on Differential Cross Sections and Angular Correlation Parameters for Electron Excitation of Helium

The effects of local polarization and absorption potentials on differential cross sections and angular correlation parameters are studied within the distorted-wave approximation for electron excitation of the 2 1P state of helium. For examining the effect of local polarization, we have compared a recent numerical self-consistent adiabatic polarization potential for helium with the commonly used hydrogenic adiabatic polarization potential. Different radial regions for the polarization potential were studied to determine their contribution to the overall effect of polarization. Calculations are also presented which show the effects of different strengths for a local absorption potential

Spin Polarization and Differential Cross Section for Electron-Impact Excitation of the 6s6p ¹p₁ State of Mercury: Distorted-Wave Treatment

The results of the distorted-wave theory for electron-impact excitation of atoms are applied to the excitation of the 6s6p 1P1 state of mercury. The spin polarization and the differential cross section are given for unpolarized incident electron beams with energies between 25 and 180 eV. The distorted-wave results are compared with experimental data, and good agreement is found for both the spin polarization and differential cross section

Excitation of the Lowest Autoionizing Levels in Lithiumlike Ions by Electron Impact

We present theoretical, differential, and total cross sections for electron impact excitation of the lowest autoionizing levels of various lithiumlike ions (viz., Be+, B2+, C3+, O5+, and Ne7+). For these ions, the autoionizing level of interest results from excitation of an inner-shell electron. A distorted-wave Born approximation (with exchange) is used for the calculation. The present results are compared with previous theoretical calculations and it is concluded that the Coulomb-Born approach is unreliable, particularly near threshold

Effect of the Center-Of-Mass Approximation on the Scaling of Electron-Capture Fully Differential Cross Sections

We present results for p+He single electron capture and transfer with target excitation using the first Born approximation. The effect of approximating the center of mass of the helium atom and outgoing hydrogen atom at the respective nuclei is explored. Semianalytical results are compared for the calculations with and without the approximation, and it is shown that one must properly account for the center of mass of the atoms. It is also shown that this approximation is the result of the apparent v4 scaling that was previously observed with the four-body transfer with target excitation model

Role of the Ground State in Electron-Atom Double Ionization

Recently, absolute measurements have been reported for double ionization of helium by 5.6 keV electron-impact. At this high energy, one would think that the first Born approximation for the interaction of the projectile with the atom would be valid. However, on the basis of a lowest-order implementation of a Faddeev-type approach, Berakdar concluded that the approximation was not valid. Here we argue that (i) it is valid at this energy and (ii) the previous discrepancy between calculations in the first Born approximation and the overall magnitude of the measurements was due to a poor description of the ground state

Slow Convergence of the Born Approximation for Electron-Atom Ionization

It is usually assumed that the first-Born approximation for electron-atom ionization becomes valid for the fully differential cross section at sufficiently high impact energies, at least for asymmetric collisions where the projectile suffers only a small energy loss and is scattered by a small angle. Here we investigate this assumption quantitatively for ionization of hydrogen atoms. We find that convergence of the Born approximation to the correct nonrelativistic result is generally achieved only at energies where relativistic effects start to become important. Consequently, the assumption that the Born approximation becomes valid for high energy is inaccurate, since by the time it converges, nonrelativistic scattering theory is not valid