M. Salzmann

Observation of vibrational excitation in photoelectron spectroscopy of HI+ 2Π

Using photoelectron spectroscopy in combination with synchrotron radiation, we have observed previously inaccessible vibrational excitation of HI+ X 2113,z, X 2111,2 final ionic states. The vibrational enhancement is shown to be caused by strongly predissociating autoionization resonances converging to HI+ A ?Z+. Molecular vibrational constants are extracted from the photoelectron spectra obtained at different excitation energies.

Angle-resolved measurements of the photoelectron spin polarization in the photoionization of HI molecules

Using circularly polarized synchrotron radiation, the 5p pi ionization of HI molecules is studied by means of angle-resolved photoelectron spin polarization spectroscopy. The energy dependences of the dynamical photoionization parameters are obtained and compared with an ab initio calculation of Raseev et al. (1987) and the corresponding data for the xenon atom. Angular distributions of the polarization component A( Theta ) yield complete parameter sets. A strong influence of electronic autoionization is observed and analysed in terms of partial contributions using the additional information contained in the polarization results.

Spin-resolved photoelectron spectroscopy of HBr in the resonance region of electron autoionization

The spin polarization parameters A and xi , the cross section sigma and the angular distribution parameter beta in outer shell photoemission from HBr were measured in the resonance region of electronic autoionization between the HBr+ X 2 Pi and HBr+ A 2 Sigma + thresholds using photoelectron spectroscopy with circularly polarized synchrotron radiation. In this region the photoelectron spectra display pronounced vibrational excitation of the X 2 Pi final ionic states. The energy dependence of the dynamical parameters is strongly influenced by electronic autoionization and predissociation of vibrational progressions of Rydberg states. The data for sigma and A are combined to obtain cross sections for the outgoing partial waves. A comparison of the experimental results with ab initio MQDT calculations of Lefebvre-Brion(1989) indicates that predissociation is more important than theoretically predicted.

Spin polarization of Auger- and of photoelectrons from barium atoms exposed to circularly polarized radiation and their cross comparison

New results of spin polarization of both photoelectrons and Auger electrons are reported after 5p photoionization of free Ba atoms with circularly polarized light. A substantial polarization transfer from the spin polarized photons to the spin polarized photoelectrons and via the hole state orientation to the spin polarized Auger-electrons is observed. The cross comparison of the results for photoelectrons and Auger-electrons allows a quantitative test of the assumed two step model where both electron-emission processes occur in sequence.

Angle- and spin-resolved photoelectron spectroscopy of thepπ outer valence shell of HBr molecules

Using circularly polarized synchrotron radiation, the photoionization of HBr molecules was studied by angle- and spin-resolved photoelectron spectroscopy in the photon energy range from 11.7 eV to 21 eV. For photoelectrons corresponding to the final ionic states HBr+X2Π3/2(v=0) andX2Π1/2(v=0), the energy dependence of the dynamical photoionization parameters was measured and compared with ab initio calculations for HBr+ by Raseev et al. and RRPA calculations for Kr+ by Huang et al., This comparison indicates that, for energies above the electronic autoionization region, photoemission from the outer valence orbital exhibits distinct atomic behavior. By combining the experimental data for the cross section σ and the spin polarization parameter A, sums of partial cross section contributions to σ were determined and analyzed to obtain specific information on the outgoing partial electron waves. Furthermore, the validity of the so-called non-relativistic relationships for the dynamical photoionization parameters was tested as a function of equal photon and kinetic photoelectron energy, respectively.

Photoelectron spin polarization in autoionization of NO molecules prepared by jet cooling

The photoionization of NO molecules is studied using angle- and spin-resolved photoelectron spectroscopy with circularly polarized synchrotron radiation. The spin-orbit splitting is resolved by preparing only the X 21/2 component of the ground state in a helium-seeded supersonic expansion. A pronounced spin polarization in the angular distribution is found for the cold beam when the strong autoionization resonance at 13.82 eV photon energy is excited. The polarization parameters A, and are determined for the v = 2 and 3 vibrational levels of the NO+ X 1+ final ionic state. The results lead to the conclusion that resonances with 2+ and 2 symmetry contribute with similar intensity. The dominant contributions to the dipole transition matrix elements of the emitted electron waves can be derived approximately.

Spin polarization of photoelectrons from zinc atoms in the autoionization region

We have measured the energy dependence of the dynamical spin-polarization parameters for photoelectrons from zinc atoms in the wavelength region from 100 nm to 115 nm. The pronounced structure near the resonances found in previously measured absorption spectra also occurs in the spin-polarization parameters. From the experimental results the dipole transition matrix elements including the relative phase shift difference have been determined. The data are also compared with an existing R-matrix calculation and a new calculation employing semi-empirical Slater - Condon parameters.

Photoelectron Spin Polarization Approaching Unity: Photoionization of TI

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(6’) 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.

Photoionization of an open-shell atom with open-shell final ionic state: A spin-resolved study of photoelectrons above the Tl+ (6s6p) 3P1 limit

Abstract Spin-resolved measurements of the dynamic photoionization parameters for photoelectrons from thallium atoms are presented for the Tl+ (5d106s6p) 3P1 final ionic state in the complex spectral region from 90 to 77 nm. For a complete description of this ionization process more than three transition matrix elements are needed since neither the initial nor the final state has closed-shell configuration. An approximate determination of matrix elements and phase shift differences is carried out. In addition, it is discussed how complete information may in principle be obtained.