K. Schulz

Resonance parameters of photo doubly excited helium

Using theoretical results from complex rotation calculations and data from experimental photoionization cross sections, the quantum defects, the widths, the oscillator strengths and the shape parameter of Rydberg series of autoionizing resonances in helium, excited with synchrotron radiation from the ground state, are reviewed and analysed systematically. The relation of these resonance properties to the propensity rules for radiative and non-radiative transitions in two-electron atoms is established.

Vibrationally resolved Si 2p photoabsorption spectrum of SiF4

Abstract A high-resolution study of the Si 2p photoabsorption spectrum of gas-phase SiF 4 is reported. In the excitation region of the Rydberg orbitals, vibrational substates from symmetric stretching vibrational modes were resolved, which were described on the basis of a Franck-Condon analysis resulting in vibrational energies and equilibrium interatomic distances of the core-excited molecule. The natural lifetime width of the Si 2p core excitation amounts to 85 meV, a value that is substantially larger than the theoretically predicted one.

Photoabsorption study of ligand-field splitting of Br-3d levels in HBr

The inner-shell photoabsorption spectrum of gas-phase HBr below the Br-3d ionization thresholds was measured with high spectral resolution. Ligand-field splitting of the Br-3d levels could be clearly resolved in photoabsorption, in agreement with observations made in recent photoemission work. The good signal-to-noise ratio of the present photoabsorption spectrum allowed to follow the ligand-field splitting of 3d-core-excited np Rydberg states up to high quantum numbers (n=9), and to assign some additional weak transitions that could not be resolved before.

Photoionization study of doubly-excited helium at ultra-high resolution

Abstract The doubly-excited states of He were studied at the 9.0.1 undulator beamline of the Advanced Light Source. Using a 925 lines/mm grating and entrance/exit slits as narrow as 2.5 μm, the (2p,3d) state could be observed with a total experimental width of 1.0 meV (FHWM), which corresponds to a resolving power of Efrsol|E/gDE = 64,000 at hv = 64.12 eV. With this substantially reproved resolution, we reinvestigated the photoionization spectrum of He up to the double-ionization threshold at ∼= 79 eeV. Some previously unobservable Rydberg states and Rydberg series were identified, and the results are compared with state-of-the-art atomic-structure calculations as well with the results of a systematic study performed recently at the SX700/II beamline at BESSY.