Hollow Li2+(2s) production in a collision between a fast electron and a neutral lithium target is studied theoretically by a procedure which determines the fully-differential cross section of the corresponding (e, 3e) process. The calculated cross sections are obtained within the framework of the first Born approximation. The two slow emitted electrons in the continuum are described by the fully correlated three Coulomb interactions (3C). The results are compared to those of the double ionization of lithium resulting in a residual Li2+(1s). The comparison between these two channels is essential to get precious indication of the different mechanisms in double ionization of a three-electron target and to observe directly electronic correlation, which is the main cause of the double ionization by fast electron impact.
The double ionization of helium by electron impact for $106\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ incident energy was studied in a kinematically complete experiment by using a reaction microscope. The pattern of the angular correlation of the three emitted electrons was analyzed by selecting different values of the recoil ion longitudinal momentum. The Wannier predicted geometry appears when the recoil ion carries the full initial projectile momentum. It was found that at this low impact energy, the outgoing electrons still remember the initial-state collision information.
A photon-ion merged beam endstation has been set up at the variable polarization XUV-beamline P04 of PETRA III in Hamburg. In a commissioning experiment first results could be obtained for multiple photoionization of Xeq+ ions (q = 1,2,..,5) at photon energies around the 3d ionization threshold.
We present experimental and theoretical fully differential cross sections for single ionization by fast, 1-keV $(v=8.6\phantom{\rule{0.3em}{0ex}}\text{a.u.})$ electron impact. The cross sections were measured using a momentum imaging technique for electrons and ions (reaction microscope), which covers a large fraction of the emission angles for emitted low-energy electrons $(E<15\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ and a wide range of scattering angles. Therefore comprehensive data sets are obtained for ionizing collisions at small relative momentum and energy transfer from the projectile to the target system. The experimental data are compared with predictions from several state-of-the-art theoretical calculations. At this high impact energy the calculated cross section for electron emission out of the scattering plane appears to be particularly sensitive to the treatment of higher orders in the projectile-target interaction within perturbative models.
We report a combined experimental and theoretical study of the ionization dynamics of tetrahydrofuran induced by 250 eV electron impact in which the highest occupied molecular orbital is ionized leading to the stable parent ion. Experimentally a reaction microscope was used, covering nearly the entire $4\ensuremath{\pi}$ solid angle for the ejected slow electron. We present the triple-differential cross sections for the projectile scattering angles of ${\ensuremath{\theta}}_{1}$ = $\ensuremath{-}{10}^{\ensuremath{\circ}}$ as a function of the emission angle of the ejected electrons with energies of ${E}_{2}=10$, 15, and 20 eV, i.e., for asymmetric energy sharing between the scattered and ejected electrons. The measured triple-differential cross sections are internormalized across the three ejected energies. The experimental data are compared with predictions from the molecular three-body distorted-wave (M3DW), the multicenter distorted-wave (MCDW) approaches, and a modified MCDW-WM method which includes the postcollision interaction using the Ward-Macek approximation. Generally, the M3DW cross sections show better agreement with experiment than the MCDW calculations except for the emission angles near the projectile forward direction. The MCDW and MCDW-WM calculations do not reproduce the recoil lobes and show very small intensity for the cross sections outside the scattering plane.
We report a combined experimental and theoretical study on the electron-impact ionization of helium at ${E}_{0}\phantom{\rule{0.28em}{0ex}}=\phantom{\rule{0.28em}{0ex}}70.6\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$ and equal energy sharing of the two outgoing electrons (${E}_{1}={E}_{2}=23\phantom{\rule{0.28em}{0ex}}\mathrm{eV}$), where a double-peak or dip structure in the binary region of the triple differential cross section is observed. The experimental cross sections are compared with results from convergent close-coupling (CCC), $B$-spline R-matrix-with-pseudostates (BSR), and time-dependent close-coupling (TDCC) calculations, as well as predictions from the dynamic screening three-Coulomb (DS3C) theory. Excellent agreement is obtained between experiment and the nonperturbative CCC, BSR, and TDCC theories, and good agreement is also found for the DS3C model. The data are further analyzed regarding contributions in particular coupling schemes for the spins of either the two outgoing electrons or one of the outgoing electrons and the $1s$ electron remaining in the residual ion. While both coupling schemes can be used to explain the observed double-peak structure in the cross section, the second one allows for the isolation of the exchange contribution between the incident projectile and the target. For different observation angles of the two outgoing electrons, we interpret the results as a propensity for distinguishing these two electrons---one being more likely the incident projectile and the other one being more likely ejected from the target.
An experimental method is described to obtain electron spectra with good resolution and high intensity following L-shell excitation or ionization of laser-excited Na atoms. We report on experimental and theoretical electron spectra in the energy range of 25 - 33 eV for laser excitation to , , and and for 1.5 keV electron impact. Due to the good agreement in line positions and intensities essentially all lines can be assigned. Furthermore, experimental relative cross sections for states excited from , and are determined and compared with theoretical values.
The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)].
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