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[en] Single-photon ionization of an atom or molecule can be subdivided into parity-favored and -unfavored transitions, the latter characterized by electron emission, preferentially perpendicular to the electric vector. The nonresonant existence of these transitions is shown experimentally and studied over an extended energy range for a variety of satellite transitions in atomic argon. The spectra exhibit several clearly resolved satellite lines with strongly negative β values close to -1, independent of the photon energy. The results confirm the corresponding predictions of angular-momentum transfer theory

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No abstract available

[en] Helium photoelectron satellites He⁺ nl (n = 2-7) have been studied with monochromatized synchrotron radiation. The angular distributions were determined in the photon energy range from 80 eV to 603 eV showing, for all of the observed satellites, increasing angular distribution parameters β which converge to β 2 at high photon energies. The overall behaviour shows a clear tendency of reduced fractional intensity of s-like orbitals for states with higher principal quantum numbers n. In addition, at lower photon energies the satellites with higher n tend to have lower β-values reflecting the influence of higher angular momenta near threshold. (author)

[en] Angular distributions of C(1s) photoelectrons emitted from oriented CO molecules were measured using a new method: mass and angle-resolved photoelectron-photoion coincidence spectroscopy. Along with the angular momentum composition of the photoelectron wave, the experiment reveals pronounced forward-backward asymmetries in the photoemission intensity with respect to the molecular orientation. This asymmetry, being observed for the first time in molecular photoionization, is interpreted in terms of multiple scattering effects. Calculations using the MS-Xα method show good quantitative agreement with the presented experimental results. copyright 1997 The American Physical Society

[en] Helium double photo-ionization is studied by a novel coincidence technique which employs time-of-flight spectrometers. Using this technique it is possible to collect simultaneously all the electron pairs, with different energy sharing, emitted by the absorption of a single energetic incident photon. The measurements, in a configuration where the two electrons emerge at 180^o relative angle, provide the more complete information on the contribution of the ungerade amplitude to the triple differential cross section and allow the establishment of a relative scale for the full coincidence angular distribution measured by other experiments at the same photon energies, but only for a few selected energy-sharing conditions. (author)

[en] Neutral hydrogen atoms with energies ranging from about 1 to 20 keV are scattered from a clean and flat LiF(0 0 1) surface under grazing angles of incidence. By detection of time-of-flight (TOF) spectra in coincidence with the signal of an electron number detector, we study electron emission and excitation phenomena. We present recent progress in an on-line processing of spectra by means of a double coincidence unit

[en] Full text: Photoion yield measurements in the valence photoionization region of C₆₀ reveal a high fraction of doubly and even triply charged ions above 70 eV. This fractional intensity increases continuously from the threshold to the sudden limit value, which is in close accordance with the adiabatic transition model of T. D. Thomas. The experimental data are shown together with the model curves in. The results point to shake-off as the mechanism for multiple ionization. But which part of the valence photoelectron spectrum corresponds to the multiple ionization events? To find this out, we compared complete valence electron spectra, including all low-energy electrons, with the photoion data. Electron-ion as well as electron-electron coincidence experiments are a tool to obtain more direct information on these processes

No abstract available