E. Shigemasa

New setup for angular distribution measurements of Auger electrons from fixed in space molecules

A new experimental setup for measurement of the angular distributions of energy selected Auger electrons emitted from fixed in space molecules is presented. The system is based on two identical ion detectors with a small angular acceptance placed at 0° and 90° relative to the polarization axis of the incident radiation, and a high luminosity double-toroidal electron analyzer combined with position sensitive detection. This setup allows selection of the molecular alignment for σ and π ionization channels simultaneously and provides an energy and ejection angle measurement of the outgoing electron. The performance in terms of energy and angular resolution, as well as the calibration procedure, are discussed. Sample results obtained on the carbon monoxide ionized above the C 1s threshold are presented.

Photofragmentation study of hexamethyldisiloxane following core ionization and direct double ionization

X-ray photoelectron spectroscopy and Auger spectroscopy studies of gas-phase hexamethyldisiloxane (HMDSO) are presented. The photodissociation of this molecule is studied using various experimental coincidence techniques. We compare the fragmentation pathways observed after core ionization followed by Auger decay and after valence double photoionization of the molecule. A strongly selective production of the doubly charged tetramethyldisiloxane ion is observed in the low binding-energy regions. Theoretical calculations are carried out to tentatively explain the stability of the produced dication.

Multielectron coincidence spectroscopy for core-valence doubly ionized states of CO

Double photoionization into states which have holes in one core and one valence orbitals has been observed in CO using a state-of-the-art multielectron coincidence method. The core-valence CO2+ structures exhibited on the electron coincidence spectra are assigned by comparison with the available calculation [H. Schulte et al., J. Chem. Phys. 105, 11108 (1996)]. Features of the spectrum confirm that the properties of the CO2+ states are characterized by the interaction between the localized valence holes and the core holes.

Development of symmetry-resolved zero-kinetic-energy photoelectron spectroscopy for probing multielectron processes

A new experimental setup for probing multielectron processes in molecular inner-shell ionization regions has been developed. Symmetry-resolved zero-kinetic-energy (ZEKE) spectra have been measured by scanning the photon energy along with monitoring the intensity of the coincidence signals between ZEKE electrons and fragment ions detected at 0° and 90° relative to the electric vector of the light. The actual performance of the method is illustrated by using it to reveal the symmetry decomposition of the multielectron processes, such as double excitations and shake-up satellites, in the K-shell ionization region of nitrogen.

New molecular inner-shell spectroscopy for probing multiple excitations

A new experimental setup for probing multi‐electron processes in molecular inner‐shell ionization regions has been developed at the UVSOR facility, IMS. A zero‐kinetic‐energy electron (ZEKE) analyzer is composed of a lens system on the basis of the penetrating field technique and an electrostatic analyzer. Two identical ion detectors with regarding grids are utilized for detecting the fragment‐ions emitted at 0 and 90 degrees relative to the electric vector of the light, which correspond to the symmetry‐resolved photoabsorption spectra. The symmetry‐resolved ZEKE spectra have been measured by scanning the photon energy with monitoring the intensity of the coincidence signals between the ZEKE electrons and fragment‐ions. The results obtained at SPring‐8 using the new setup are reported.

Observation of an optical vortex beam from a helical undulator in the XUV region

The observation of an optical vortex beam at 60 nm wavelength, produced as the second-harmonic radiation from a helical undulator, is reported. The helical wavefront of the optical vortex beam was verified by measuring the interference pattern between the vortex beam from a helical undulator and a normal beam from another undulator. Although the interference patterns were slightly blurred owing to the relatively large electron beam emittance, it was possible to observe the interference features thanks to the helical wavefront of the vortex beam. The experimental results were well reproduced by simulation.

Dissociation of core-valence doubly excited states in NO followed by atomic Auger decay

The decay processes of core-valence doubly excited states near the N K edge of NO have been studied using electron spectroscopy. Electron yields measured as a function of photon energy and kinetic energy enable the clear identification of atomic Auger lines associated with the dissociation of doubly excited states. The atomic Auger lines exhibit Doppler profiles, allowing the entire reaction scheme of such dissociation processes to be determined.

Single, double, and triple Auger decay of the Xe 4p core-hole states

Auger decay of Xe{sup +} states arising from 4p ionization has been studied with a very efficient multielectron coincidence method. Coster-Kronig decay from Xe{sup +} 4p{sup -1} and the subsequent decay into Xe{sup 3+} states with three valence holes are identified. Formation of Xe{sup 4+} is also observed as quadruple coincidences between a 4p photoelectron and three Auger electrons. The relative probabilities of individual multi-ionization processes are determined from the coincidence yields.

Status and Prospects of User Applications of the UVSOR Storage Ring Free Electron Laser

Because of in addition to the high out‐coupled power and a good coherence, the temporal feature that the laser pulse is naturally synchronized with the SR pulse, the SRFEL is a powerful tool for application experiment. At UVSOR, we have performed an application experiment of the SRFEL on the two‐photon double‐resonant excitation of the Xe. The storage ring is temporary shutdown now to upgrade its performance. The improve performance of the electron beam is of great advantage for the SRFEL and its application.

Stability of Auger final dicationic states of core-ionized N2 molecules studied by Auger-electron ion coincidence measurements

We present experimental results for AEPICO measurements following core photoionization of N2 molecules, with using an AEPICO spectrometer in which a toroidal electron energy analyzer and an ion momentum spectrometer are installed.