A new method for the size-selective EXAFS of neutral free clusters

Recently we have measured Photoelectron Photoion Coincidence (PEPICO) spect ra for selenium dimer Se-2 and larger species such as Se-5 at the beamline BL-12C in Photon Factory. The PEPICO spectra reveal that the multiply charg ed ions, Sez+, are produced as a result of de-excitation processes followin g the inner-shell excitation and fragmented to atomic ions owing to the Cou lomb explosion. The branching ratios from the parent clusters to the daught er ions exhibit clear dependence on the size of the parent clusters. In par ticular, the branching ratios in the non-resonant absorption region are wel l reproduced by assuming that the charges are randomly distributed within t he clusters before the Coulomb explosion. Based upon these findings, we pro pose a new method for the size-selective EXAFS of neutral free clusters by utilizing the PEPICO measurements.