F. Schäfers

High‐flux normal incidence monochromator for circularly polarized synchrotron radiation

A 6.5‐m normal incidence monochromator installed at the storage ring BESSY, which is optimized for a high throughput of circularly polarized off‐plane radiation at moderate resolution is described. The monochromator employs two exit slits and is specially designed and used for low‐signal experiments such as spin‐ and angle‐resolved photoelectron spectroscopy on solids, adsorbates, free atoms, and molecules. The Monk–Gillieson mounting (plane grating in a convergent light beam) allows for large apertures with relatively little astigmatism. With two gratings, a flux of more than 1011 photons s−1 bandwidth−1 (0.2–0.5 nm) with a circular polarization of more than 90% in the wavelength range from 35 to 675 nm is achieved.

Measurements and calculations of the circular polarization and of the absolute intensity of synchrotron radiation in the wavelength range from 40 to 100 nm

Abstract The circular polarization and the absolute intensity of the elliptically polarized synchrotron radiation were measured in the VUV range as functions of the wavelength and of the vertical emission angle with respect to the orbit plane of the 2.5 GeV synchrotron in Bonn. In the wavelength range from 100 to 40 nm the absolute intensity and the circular polarization of the radiation with a bandwidth of 0.05 nm has been experimentally determined to be between 10 9 and 10 10 photons s −1 and (83±3)%, respectively. The experimental data are compared with calculated results obtained on the basis of Schwingers theory taking into account the properties of the synchrotron as well as of the components in the 10 m normal incidence monochromator.

A high flux normal incidence monochromator for circularly polarized synchrotron radiation

Design and performance of a 6.3 m normal incidence UHV-monochromator (see fig. 1) of the Gillieson type for synchrotron radiation are described. The monochromator will be used for simultaneously spin polarization and emission angle-resolved photoelectron spectroscopy; it combines a high photon flux and a high degree of circular polarization of the monochromatized radiation with a moderate resolution.

Spin polarized photoelectrons from CO2 and N2O

The photoelectrons emerging from unpolarized CO2 and N2O molecules exposed to circularly polarized synchrotron radiation are spin polarized After a brief description of the apparatus the polarizations measured at the ionization threshold are presented and compared in the case of CO2, with a calculated, in an ab initio theory obtained value. Using the spin density matrix formalism a general expression for the spin polarization as a function of the dipole matrix elements is presented.

Analysis of Autoionization Resonances in the Hg 6s2-Photoionization by Measurements of Photoelectron Polarization

Measurements of the spin polarization of photoelectrons in the autoionization region of the Hg 6s2-subshell using circularly polarized synchrotron radiation and using unpolarized light from rare gas discharge lamps are reported. The results obtained show a pronounced structure across the resonances. Together with data of the cross section and its angular distribution these data from a complete parameter set for the determination of the transition matrix elements and the phase difference of the continuum wavefunctions. Evidences for strong configuration interaction and channel mixing between the open and closed channels were found. The matrix elements and their ratio vary strongly across the resonances and the relative phase shows some changes of sign. A change of the relative phase by π across an autoionization resonance, predicted by Fano, has been verified experimentally for the triplet resonance.

Spin-polarised photoelectrons produced from CH3Br molecules by unpolarised and circularly polarised vuv radiation

It has been experimentally verified for CH3Br that spin-polarised photoelectrons can be ejected from unoriented molecules if the radiation is circularly polarised or even unpolarised. The polarisation values and the experimental data of the asymmetry parameter beta are discussed by use of Cherenkovs formulae (1981).

Determination of partial photoionisation cross sections of methyl bromide in the first autoionisation range by use of spin polarisation photoelectron spectroscopy

Using recent experimental data on photoelectron spin polarisation combined with the high-resolution spectrum of methyl bromide, which has also been recently reported, the partial photoionisation cross sections for the ionisation of CH3Br from the 4 pi ground-state orbital into the energy degenerate continua epsilon sigma , epsilon pi and epsilon delta have been determined separately. Quantitative results, obtained for the autoionising resonances between 116 and 118 nm, are reported and discussed.

Spin-polarised photoelectrons from krypton and argon atoms exposed to circularly polarised synchrotron radiation

Circularly polarised synchrotron radiation has been used to produce spin-polarised photoelectrons from krypton and argon atoms (Fano effect (1969)). The results obtained experimentally in the autoionisation and the continuum regions are presented and discussed. In the case of argon they are compared with Lees (1974) theoretical prediction.

Polarised photoelectrons produced at xenon atoms by circularly polarised synchrotron radiation

Circularly polarised synchrotron radiation is used for producing spin polarised photoelectrons at xenon atoms. After a brief description of the apparatus the dependence of the electron polarisation on the photo energy is presented and compared with a theoretical prediction.

Experimental characterization of the Xe 5p photoionization by angle- and spin-resolved photoelectron spectroscopy

Spin- and angle-resolved photoelectron spectroscopy with elliptically polarized radiation has been used to fully characterize the dynamics of photoelectron emission from free Xe atoms in the 5p-autoionization and continuum region. An advantageous reaction geometry and its experimental realization at the storage ring BESSY are discussed. The three independent experimental parameters which characterize the angular dependence of the photoelectron spin-polarization vector are reported for the wavelength range from 100nm to 40 nm. The results are compared with theoretical predictions based on RRPA-, RPAE- and semiempirical MQDT-calculations. The combination of existing data for the differential photoionization cross section with the spinpolarization parameters is used to completely decouple the photoionization channels: The transition matrix elements and their relative phases are determined separately for every single dissociation channel. The results are discussed in the context of the MQDT. Correlation effects and the influence of spin-orbit interaction on the continuum states most clearly show up when the Dill-Fano angular-momentum-transfer formalism is applied.