[en] For spectral diagnosis, a repetitive laser-produced soft-X-ray source was examined in the range 2-40 nm using a spectrometer containing a pinhole transmission grating, an image converter, and a CCD camera. Via digital recording the detection system provides fast on-line data accumulation with spectral and spatial resolution. With this detector the performance of the light source was studied with respect to spectral emission characteristics, long-term stability, and reproducibility by recording spectra for different solid targets and liquid lead. (author)

[en] In experiments described here, xenon atoms are excited to 5p ⁵6p during a collision by two-photon laser excitation. We measure the probability for collision pairs to dissociate to specific product channels following the half-collision on the excited potential curve. Within the quasistatic range of the absorption line, the initial internuclear separation for this half-collision can be controlled by the laser detuning. As we excite pairs with smaller internuclear separation, we observe a large decrease in the probability for formation of the diabatic dissociative channel. A Landau-Zener model for the first half-collision is in agreement with the data

[en] A highly resolving apparatus for molecular photoionization experiments based on resonantly enhanced sum-frequency mixing is discussed. The VUV source, based upon commercially available laser equipment, delivers more than 10¹¹ photons/second at a bandwidth of 0.38 cm^-1 with linear or circular polarization. Results of photoelectron yield measurements obtained for the complete (n^* = 6) Rydberg order of the autoionization resonances in the region of the spin-orbit split ²Π states of the HI⁺ ion are presented. In addition, measurements of the angle-integrated spin-polarization of the photoelectrons, ejected by circularly polarized radiation (Fano effect) are discussed. (orig.)

[en] Xenon atoms are excited to 5p⁵6p[(1/2)]₀ during a collision using two-photon laser excitation. The probability for subsequent fluorescence is measured as a function of laser detuning into the line wing of the transition. This probability is found to decrease significantly for large detunings corresponding to excitation of collision pairs at smaller internuclear separations. We interpret the decrease in fluorescence as inelastic quenching to dissociative channels encountered during the first half-collision

[en] A novel experiment on elastic electron scattering from free, spatially oriented molecules has been performed. CH₃I molecules state selected by an electrostatic hexapole lens were oriented in a homogeneous electric field. The differential scattering cross sections were measured at an electron energy of 1 keV in the angular range of 4 degree--14 degree with the orientation switched on and off. From these data the orientation-dependent contribution to the molecular interference was determined. The results show a distinct oscillatory pattern as a function of momentum transfer as predicted by theory

[en] Using linearly polarized Ar I line radiation for ionization, the energy- and angle-resolved photoemission from continuous wave-laser-excited aligned Yb atoms in the (6s6p) ³P₁ state is studied. Photoelectron angular distributions have been measured for different orientations of the laser polarization vector relative to the polarization vector of the ionizing radiation. From polynomial fit coefficients for these distributions the ratio of reduced dipole matrix elements and the phaseshift difference for the transitions 6p→εs and 6p→εd have been obtained at a photoelectron energy of 7.8 eV. (author)

[en] It is shown that a complete photoelectron-spin polarization occurs independent of emission angle for two special sets of values of the dynamical photoionization parameters. In spin- and angle-resolved photoelectron spectroscopy of thallium the dynamical parameters were measured near the autoionization resonances at 149 nm and 82 nm. A pronounced angular variation of the polarization component A(θ) was observed at 83 nm. For both resonances the parameters were found to approach different limiting values such that the length of the spin-polarization vector assumes values close to unity at all emission angles. The implications of these results for the corresponding dipole transition matrix elements are discussed. (orig.)

[en] The autoionization region of mercury was investigated with spin- and angle-resolved photelectron spectroscopy between the Hg⁺ (5d⁹ 6s²)²D_5/2 and Hg⁺ (5d⁹ 6s²)²D_3/2 thresholds. Spin-polarization parameters A and ξ and intensity were measured separately for the photoelectrons corresponding to the two final ionic states accessible (²S_1/2, ²D_5/2) as function of the radiation wavelength. The data are dominated by structure due to autoionization resonances and differ quantitatively for the two peaks in the photoelectron spectra. The results are compared with earlier measurements below the ²D_5/2-threshold. (orig.)

[en] Photoelectron spin-polarisation measurements of In(5s²5p) ²P_1/2 were performed in the autoionisation region of the 5s5p²-configuration using monochromatic circularly polarised synchrotron radiation at the electron storage ring BESSY. The autoionising levels are analysed in terms of partial cross section, dipole matrix elements and phase-shift differences. In addition the measured photoelectron spin-polarisation data were used for an independent check for the assignments of the autoionising levels. (orig.)

[en] The spin-polarisation parameters for photoelectrons from lead atoms (6s²6p²)_J=0 were measured in the wavelength range between the second threshold [Pb⁺ (6s²6p) ²P_3/2] and 100 nm in an angle-resolving experiment using circularly polarised vuv-radiation from the storage ring BESSY. Beyond this threshold (λ = 135.3 nm), the photoionisation cross section is strongly perturbed by autoionisation resonances. Especially, a strong enhancement of the generally weak Pb⁺ (6s²6p) ²P_3/2 photoionisation cross section occurs. Theoretical calculations by Radojevic attribute these resonances to the 6s6p³-configuration of lead. By use of the measured spin-polarisation parameters A, ξ and α which show pronounced variations in the region investigated for both final ionic states ²P_1/2 and ²P_3/2 a detailed discussion of the resonances is performed. (orig.)