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Aufsatz
Theory for the optical properties of small Hg_n clusters
(1991)
The static and dynamical polarizabilities of the Hg-dimer are calculated by using a Hubbard Hamiltonian to describe the electronic structure. The Hamiltonian is diagonalized exactly within a subspace of second-quantized electronic states from which only multiply ionized atomic configurations have been excluded. With this approximation we can describe the most important electronic transitions including the effect of charge fluctuations. We analyze the polarizability as a function of the intraatomic Coulomb interaction ...
Aufsatz
Time-resolved studies of neutral and ionized Na_n clusters with femtosecond light pulses
(1993)
The real-time dynamics of Na_n (n=3-21) cluster multiphoton ionization and fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Three dimensional wave packet motions in the trimer Na_3 ground state X and excited state B have been observed. We report the first study of cluster properties (energy, bandwidth and lifetime of intermediate resonances Na_n^*) with femtosecond laser pulses. The observation of four absorption resonances ...
Aufsatz
Femtosecond dynamics of molecular and cluster ionization and fragmentation
(1993)
The real-time dynamics of molecular (Na_2 . Na_3) and cluster Na_n (n=4-2l) multiphoton ionization and -fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Wave packet motion in the dimer Na_2 reveals two independent multiphoton ionization processes while the higher dimensional motion in the trimer Na_3 reflects the chaotic vibrational motion in this floppy system. The first studies of cluster properties (energy, bandwidth ...
Aufsatz
Theory for the change of bond character in divalent-metal clusters
(1991)
To determine the size dependence of the bonding in divalent-metal clusters we use a many-electron Hamiltonian describing the interplay between van der Waals (vdW) and covalent interactions. Using a saddle-point slave-boson method and taking into account the size-dependent screening of charge fluctuations, we obtain for Hg_n a sharp transition from vdW to covalent bonding for increasing n. We show also, by solving the model Hamiltonian exactly, that for divalent metals vdW and covalent bonding coexist already in the dimers.
Aufsatz
Photoionization of Kr near the 4s threshold: I. Experiment and LS coupling theory
(1993)
Absolute cross sections for the transitions of the Kr atom into the 4s^1 and 4p^4nl states of the Kr^+ ion were measured in the 4s-electron threshold region by photon-induced fluorescence spectroscopy (PIFS). The cross sections for the transitions of the Kr atom into the 4s^1 and 4p^4nl states were also calculated, as well as the 4p^4nln'l' doubly excited states, in the frame of LS-coupling many-body technique. The cross sections of the doubly-excited atomic states were used to illustrate the pronounced contributions ...
Aufsatz
Influence of the interaction potential on simulated sputtering and reflection data
(1992)
The TRIM.SP program which is based on the binary collision approximation was changed to handle not only repulsive interaction potentials, but also potentials with an attractive part. Sputtering yields, average depth and reflection coefficients calculated with four different potentials are compared. Three purely repulsive potentials (Meliere, Kr-C and ZBL) are used and an ab initio pair potential, which is especially calculated for silicon bombardment by silicon. The general trends in the calculated results are similar ...
Aufsatz
Fluorescence studies on the 3d-ionization threshold range in krypton
(1994)
Krypton atoms were excited by photons in the energy range from the threshold for photoionization of the 3d-electrons up to 120 eV. and the fluorescence radiation in the spectral range from 780 to 965 A was observed and analyzed. Cross sections for the population of excited states in KrIII with at least one 4s-hole resulting from an Auger transition as the first decay step and for KrII satellites were determined. The energy dependence of the 3d-ionization cross section in the 3d{_5/2}- and the 3d{_3/2}-threshold range ...
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State-selective study of the direct double photoionization of the Ne valence shell
(1993)
Cross sections for double photoionization of the Ne L shell into the 2s2p{^5 3}P^0} and ^1P^0 and the 2s^02p^6 ^1S^e states were measured for energies from threshold up to 150 eV, using photon induced fluorescence spectroscopy. Both 2s2p^5 channels were observed with comparable magnitude in contradiction to a propensity rule based on the Wannier-Peterkop-Rau theory. A comparison of the summed ^3P^0 and ^1P^0 cross sections with MBPT calculations results in a deviation of 50%.
Aufsatz
Absolute Kr 4s-electron photoionization cross sections between 30 and 90 eV measured by photon-induced fluorescence spectroscopy (PIFS)
(1994)
Absolute Kr 4s-electron photoionization cross sections as a function of the exciting-photon energy between 30 and 90 eV were measured by photon-induced fluorescence spectroscopy (PIFS). The measurements were compared with available experimental data and theoretical calculations.
Aufsatz
Threshold scan of the Ne 2s-electron photoionization cross edition
(1990)
The photoionization of the Ne 2s-electrons was studied from threshold to 1 eV above threshold. The technique of photon-induced fluorescence spectroscopy was applied. Pronounced structures were observed resulting from autoionization of doubly excited atomic states. A threshold cross section of 0.17 Mb was determined.