Abstract
The photon energy dependence of the photoelectron photoion coincidence (PEPICO) spectra near the Se K-edge have been measured for Se2 and larger species such as Se5 at the BL-12C in Photon Factory. The PEPICO spectra reveal that the multiply charged ions, Sez+, are produced as a result of the de-excitation process following the inner-shell excitation. Two prominent structures corresponding to the π* and σ* resonances are clearly observed in the energy dependence of the branching ratio from Se2, while only one structure corresponding to the σ* resonance can be seen for the larger species. At the σ* resonance, the production of Se+ and Se2+ is enhanced, in comparison with the direct ionization where the core-hole states are completely relaxed before the dissociation. The energies of the π* and σ* resonance relative to the 1s ionization potential are estimated at -10.0± 0.5 eV and -5± 1 eV, respectively. In addition, we propose a new method for the size-selective structural analysis of clusters by utilizing the PEPICO measurements.
