Georg Prümper

Isotope-induced partial localization of core electrons in the homonuclear molecule N2

Because of inversion symmetry and particle exchange, all constituents of homonuclear diatomic molecules are in a quantum mechanically non-local coherent state; this includes the nuclei and deep-lying core electrons. Hence, the molecular photoemission can be regarded as a natural double-slit experiment: coherent electron emission originates from two identical sites, and should give rise to characteristic interference patterns. However, the quantum coherence is obscured if the two possible symmetry states of the electronic wavefunction (‘gerade’ and ‘ungerade’) are degenerate; the sum of the two exactly resembles the distinguishable, incoherent emission from two localized core sites. Here we observe the coherence of core electrons in N2 through a direct measurement of the interference exhibited in their emission. We also explore the gradual transition to a symmetry-broken system of localized electrons by comparing different isotope-substituted species—a phenomenon analogous to the acquisition of partial ‘which-way’ information in macroscopic double-slit experiments.

The photoionization and fragmentation of C60 in the energy range 26-130 eV

We report on experimental results for the ionization and fragmentation of C60 after excitation with synchrotron radiation in the energy range 26–130 eV. The cross-section energy dependence of the produced Cq+60 ions (q = 1, 2, 3) and charged fragments is analysed. The Cq+60-ion yields (q = 2, 3) are explained within the framework of T D Thomas model for multiple ionization.

Angle-integrated magnetic linear dichroism in valence photoionization of free oxygen atoms

The ion-counting rate was investigated in a photoionization experiment using polarized and aligned oxygen atoms and linearly polarized light. The cross section of the valence photoionization was found to depend on the angle between the polarization axis of the ionizing synchrotron radiation and the axis of atomic alignment. A significant asymmetry in the ion rates corresponding to and was observed close to the resonance. This asymmetry is caused by j-dependent resonant behaviour of the and continuum channels.

Absorption of circularly polarized VUV radiation in polarized iron vapor.

The effect of magnetic dichroism on the total ion yield of iron, i.e. in the absorption of polarized iron vapour, was observed for the first time far away from the threshold or autoionizing states. These observations can be explained by the orientation of orbital angular momentum of the 3d-electrons. This effect has not yet been observed in the absorption measurements of magnetized iron films due to the smallness of the expectation value of the orbital angular momentum in the solid targets. The details of the dynamical behaviour go beyond single-electron approximations.

Upper limits for the circular dichroism for the C 1s and O 1s core excitation of methyl oxirane

The circular dichroism in the total and partial ion yields of methyl-oxirane C3H6O was measured at the C 1s and O 1s edges. The dierence of the response of the chiral molecule to circularly polarized light with opposite handedness was found to be less than 0.2% for the total ion yield and less than 0.5% for the partial ion yield. Additionally we tried to nd a dipole allowed molecular orientation CD eect by analyzing the fragmentation in the forward and backward direction. For this eect we found an upper limit of 1-2% for all abundant ionic fragments.

High-resolution electron-ion coincidence spectroscopy of ethanol in intense laser fields

High-resolution electron-ion coincidence spectroscopy is used to (i) map correlations between electrons and ions from atomlike ionization of ethanol by intense 400 and 800 nm light pulses and (ii) disentangle the effects of dissociative multiphoton (MPI) and tunneling (TI) ionization. Electron spectra correlated with C{sup n+} (n=1,2,3) exhibit a continuum structure with a high-energy tail due to inelastic collisions involving rescattered electrons following TI, while those correlated with C{sub 2}H{sub n}O{sup +} have structure characteristic of MPI and above-threshold ionization.

INFLUENCE OF THE IONIC STATE ON O(2P) PHOTOELECTRON ANGULAR DISTRIBUTIONS

The angular distribution parameter was measured for all final ionic states (4S, 2D and 2P) of the 2p-ionization of atomic oxygen in the photon energy range from 24 to 70 eV. Deviations from the LS-independent model were observed. This effect may be caused by final-state electron-ion interaction and many-electron correlation. It was predicted by calculations.